BMS235 Physiology and Pharmacology Flashcards
What is the composition of cell membranes?
42% Lipid
55% Protein
3% Carbohydrate
Why is there a high intracellular concentration of PO42-?
Because ATP is present in cells
What are the types of transporters?
- Carriers (facilitated transport proteins) e.g. Na+Glucose transport protein
- Pumps eg. Na+K+ Pump
- Gated ion channels
What does active and passive transport require?
Active requires ATP
Passive requires a concentration gradient
What is the electrochemical driving force?
concentration gradient and potential gradient
How much can be transported in active transport?
Low turnover < 100/second
How does active transport use ATP?
ATP is hydrolysed to ADP and Pi
The phosphate binds to the protein which causes a conformational change releasing the ion
What are the characteristics of Na+/K+ ATPase?
- Ubiquitous
- Tetramere - (2alpha and 2beta subunits) - two separate gene sequences requires one for each subunit
- Electrogenic - produces negative charge as 3Na+ out and 2K+ in
Define electrogenic
Generates a charge
What is a secondary active transport protein and give an example?
Often in passive transport
- Doesn’t require ATP itself but may rely on another protein that does
Eg. Na+ Glucose go transporter requires concentration gradient created by Na+K+ pump
How much can be transported by passive transport?
High turnover 10^2 - 10^3 / second
Characteristics of passive transport
- Follows electrochemical gradient
- Highly Selective
- Maximum transport rate - becomes saturated
What are the three types of carriers?
- Uniporter - transports 1 substance
- Symporter (cotransporter) - transports 2 substances in the same direction
- Antiporter (exchanger) - transport 2 substances in opposite directions
Characteristics of ion channels
- Gated
- High turnover - 10^6 - 10^8 ions/second
- Conductive
How are ion channels conductive?
When channels are open ions flow producing a current when closed there is no current
What is the patch clamp technique?
A technique that measures the current in a cell membrane with respect to the bath where the current in 0mv and allows us to see ion channels opening and closing within cell membranes
What is the difference between open and closed patch clamp technique?
- Open measures the current flow through all of the ion channels in the cell membrane. The part of the membrane between the two glass electrodes is removed
- Closed only measures the current flow in the part of the cell membrane between the two glass electrodes
What are the uses if the patch clamp technique?
Allows identification of ion channels and allows their function and regulation to be investigated
What is the equation for the total current carried by channels?
I = N.Po.g.(Vm-Ei)
I = Total current carried by channels N= Number of channels Po= Probability that channels will be open g = Single channel conductance Vm= Membrane potential Ei = Equilibrium potential ion i
What is Vm - Ei ?
Membrane potential and equilibrium potential ion which add together to the driving force
Basic structure of K+ channel family
- 6 transmembrane domains
- 4 subunits come together to create a channel
- pore
Basic structure of Na+ channel family
- 24 transmembrane domains ( 4 groups of 6)
- Similar structure to K+ channels
What is the structure of K+ in bacteria?
- Crystal structure
- 4 subunits with a central pore
How would you measure the membrane potential (traditional intracellular method)l?
- Glass electrode filled with a KCl solution
- Silver electrode in centre measures the membrane potential with respect to the 0mV bath
What is the difference between the patch clamp method and the traditional intarcellular method?
The tip of the electrode in the patch clamp method is 1x10^-6 but in the traditional method the tip is much smaller
What is the contribution of Na+/k+ ATPase to the membrane potential?
- It directly contributes 20% of the membrane potential due to its electrogenic nature
- It also indirectly contributes to the intracellular Na+ K+
How is the Nernst potential reached by K+ ions across the membrane?
- K+ moves out of the cell due to the concentration gradient leaving a negative charge inside the cell
- This produces a potential gradient going the opposite way (Positively charged K+ ions will travel down gradient back to negatively charged inside of the cell)
- Eventually the concentration gradient and potential gradients are equal so K+ movement in both directions are equal => no net movement of K+ ions
What is the Nernst equation at body temperature?
Elon = 61/Z x log (5/150)
Why is the Nernst equation never completely accurate?
Because it is never just one type of ion channel open e.g. K+ and Na+ channels will be open so Nernst equation for just K+ won be accurate
How is the Nernst potential reached by Na+ ions across the membrane?
- Na+ moves into cell down its concentration gradient leaving a positive charge
- Na+ then repels the positive charge so creates a driving force going the opposite way
- Eventually movement of Na+ becomes equal in both directions so no net movement
What does the resting membrane potential suggest about Na+ and K+ channels?
Membrane potential for Na+ is +64mv but resting potential is -70mv suggesting Na+ channels are closed
Membrane potential for K+ is -90mv suggestion that K+ channels are open
What is the Goldmans equation at body temperature?
Vm = 61/7 log (PNa[Na+]o + Pk[K]o) / (PNa[Na]I + Pk[K+]I)
What drives the membrane potential?
Na+K+ ATPase
What causes depolarisation and hyper polarisation in the formation of an action potential?
- Massive opening of Na+ channels driving membrane potential towards nernst potential for Na+ (depolarisation)
- Na+ channels close driving Vm towards nernst potential for K+ (hyper polarisation)
What are the normal intracellular and extracellular concentrations of [Na+]?
Extracellular - 145mM
Intracelular - 15mM
Give examples of why intracellular and extracellular Na+ concentrations are important?
- Thick ascending limb - NaK2Cl cotransporter uses the Na+ gradient produced by the Na/K ATPase
- Excitable cells - Na+ ions move into the cell down the concentration gradient causing depolarisation
How does Na/K ATPase allow the exchange of Na+ and K+?
- Requires 1 ATP molecule
- ATP phosphorylates the pump leading to a conformational change, changing the binding site for Na+ releasing it
- K+ then binds causing dephosphorylation and a structural change causing the release of K+ inside the cell
Why is the rate of ion transport using Na/K described as a saturated function?
Because it has a maximum rate
Saturable function of [Na]I[k]o and ATP
What inhibits the Na/K pump?
Glycosides - ouabain and digoxin
What is the role of Na/K pump?
- Electrogenic transport of 3Na+ out and 2K+ in - make cell more negative
- Accumulation of K+ inside the cell creating a driving force for K+ to leave the cell through K channels
What are the normal intracellular and extracellular levels of Ca2+?
Extracellular - 1mM
Intracellular - 100nM
Why is calcium regulation important?
It acts as an important second messenger in many signalling pathways
e.g. Muscle contraction
What is the Nernst potential for Ca2+?
+120 mv
Why is it important to keep intracellular calcium low?
To provide a huge gradient for quick calcium entry
What are mechanisms are used to keep intracellular Ca2+ low?
Na/Ca exchanger
CaATPase
Under normal conditions what is the role of the Na/Ca exchanger?
Exchanges extracellular Na for intracellular Ca
It keeps intracellular so low by exchanging 1Ca for 3Na - electrogenic
What is the stoichiometry of the Na/Ca exchanger and why is it needed?
3Na+:1Ca2+
Because if the Na gradient was 10 fold but Ca 10000 then intracellular Ca would not be kept low if the exchanger was 1:1. Therefore 3Na means that the effect of the 10 fold gradient is cubed
What are the characteristics of the Na/C exchanger?
- They are members of the SLC8 gene family and the much larger CaCA superfamily
- Three forms exist in mammals names NCX1-3
Name the characteristics of Ca2+ ATPases
- Member of the P-type ATPase family which also includes Na/K pump
- Also pump protons in the opposite direction at the same time as transporting Ca2+
What are the three types of Ca pumps?
PMCA - plasma membrane calcium pumps
SERCA - Ca pumps found on the sarcoplasmic and endoplasmic reticulum membranes
SPCA - Ca pumps found o the Golgi apparatus
What is the role of PMCA pumps?
Act to pump Ca2+ across the plasma membrane out of the cell
What is the role of SERCA pumps?
Act to pump Ca2+ out of the cytoplasm into the organelles which act as calcium stores
What is the like of SPCA pumps?
Transport Mn2+ as well as Ca2+
What are the 4 types of Ca2+ channels?
- Voltage operated Ca Channels (VOCC)
- Receptor operated Ca channels (ROCC)
- Mechanically activated Ca Channels - found in many cells respond to deformation (e.g. stretch activated channels)
- Store operated Ca Channels (SOCC)
How are voltage operated Ca channels (VOCC) activated?
Found in excitable cells and activated by depolarisation
How are receptor operated Ca channels (ROCC) activated?
Found in secretory cells and nerve terminals and are activated by the binding of an agonist
e.g. NMDA receptor
How are mechanically activated Ca channels activated?
Found in many cells and respond to deformation eg. stretch activated channels
How are store operated Ca channels (SOCC) activated?
Activated following he depletion of calcium stores
What are the two classes of calcium channels in the store membranes?
- IP3 receptors
- Ryanodine receptors
What is an IP3 receptor?
A class of calcium channel in store membranes that is activated following the binding of IP3. This type of receptor is expressed in most cell types
What is a Ryanodine receptor?
A class of calcium channel found in store membranes that are activated by low concentrations of Ryanodine and inhibited by higher concentrations.
- Found in excitable cells
- Also stimulated by caffeine and cADP ribose
How is Ca released from stores?
- Phospholipase C (PLC) stimulates receptor in membrane forming DAG and IP3
- IP3 activates IP3 receptor channels in the stores releasing Calcium into the cytoplasm
- Signalling also from the ER to Ca channel in membrane (SOCC) which activates store refill.
How are the Ca stores refilled?
- When Ca2+ decreases in the store, the stim protein in the ER membrane senses this and undergoes a conformational change
- It stretches and binds to other stim proteins forming an 8 unit complex which binds to the cell membrane
- This interacts with ORAI1 causing Ca2+ to enter the cell
- When this happens the circa pump is stimulated favouring Ca2+ uptake into ER
What is the ORAI1?
A Ca channel in the membrane involved in refilling the Ca stores
- Tetramer like
What is the equation for pH?
pH = -log[H+]
What are the plasma and intracellular pH values?
plasma = 7.35-7.45 IC = 7-7.1
Why is regulation of pH important?
Can cause change in protein charge, conformation or function
e.g. Apical K+ channel ROMK is pH specific (activates when alkaline)
What are the two ways of measuring intracellular pH?
- Microelectrodes
- Fluorescent indicators
How is intracellular pH measured using micro electrodes?
- Uses two ion sensitive micro electrodes where one measures the voltage of all ions and the other measures everything except protons
- Take these voltages away to get the voltage of H+
- Calibrate electrodes with pH standards to work out what pH the voltage of H+ is proportional to
- Convert voltage into pH
When is it good to use microelectrodes to measure pH?
When the cells are big e.g. in the xenopus
What is a proton ionopore?
A small molecule that allows pH in a cell to equilibrate to pH outside
Outline the use of fluorescent indictors when measuring intracellular pH?
- Cells loaded with a lipid soluble form of indicator
- Inside the cell the indicator is lazed into an active form (Lipid insoluble)
- Indicator is excited with light of a specific wavelength and the amount of emitted fluorescent light at a second wavelength is measured
- Fluorescence is proportional to IC pH
How is the indicator used in measuring IC pH calibrated?
- Calibrated inside the cell
- membrane permeabilised with a proton ionopore
- pH of ionopore bath is changed
- In the presence of an ionopore bath the pH=IC pH
When is it good to use fluorescence indictors to measure IC pH?
When the cells are small eg. kidney or cardiac
What factors are involved in the control of intracellular pH?
- Buffering
- Acid extrusion
- Acid loading
What is the purpose of buffering?
To minimise pH changes and protect cells from damage
- Cant revers pH change or prevent pH changes
How does a buffer work?
moderates the effect of acid/alkali by reversibly consuming or releasing protons
Define buffering power
The amount of strong base that must be added to a solution in order to raise the pH by a given amount
How do proteins act as a buffer?
When pH increases, the COOH group from the amino acid donates a H+ becoming COO-
When pH decreases the amino acid gains a H+ on NH2 group becoming NH3+
When does acid extrusion occur?
When pH decreases
What does acid extrusion rely on?
- Na/H exchanger (NHE) pumps Na+ in and H+ out - set up Na+ gradient
- When pH is more than NHE set point then the exchanger is inactive
- Ca2+ binding to the c terminus of NHE stimulates acid extrusion
How does NHE have allosteric modification?
Protons other than the one being transported bind to the NHE protein leading to conformational change which increases the activity of the protein
What is meant by NHE1 having housekeeping functions?
Controls cell volume and regulates pH
What is NHE1 inhibited by?
low conc of amiloride and its analogue EIPA
What is acid loading?
- reduced pH as pH increases so does Cl/HCO3 exchanger activity
- moves HCO3- out of the cell and H+ in (acidification)
- has allosteric modification
Give the characteristics of AE family?
- 4 subunits
- all inhibited by stilbene derivative drug DIDS
- independant of Na+
Where is AE1 found?
- Predominantly in red blood cells, some in kidney - responsible for chloride/hamburger shift
What pressure gradients are required for inspiration and expiration to occur?
Inspiration = Patoms > Palv Expiration = Palv > Patmos
What inflation factors have to be overcome for respiration?
- Elastic recoil of tissues
- Surface tension in alveoli
- Airways resistance
Why when at rest are the elastic forces in the lungs balanced?
Elastic nature of the lungs would tend to cause them to collapse inwards
The chest wall would tend to expand
- At rest these two forces balance - as a result the pressure in the intrapleural space is less than atmospheric pressure
What is compliance?
The measure of elasticity
The ease with which the lungs and thorax expand during pressure changes
How is compliance measures?
C = ΔV/ΔP
Give an example of an illness causing low compliance?
Pulmonary fibrosis
- more work required to inspire
- Decrease in FRC
Give an example of an illness causing high compliance?
Emphysema
- difficulty when expiring
- Increase in FRC
What is function residual capacity (FRC)?
When the force of the lungs matches the expanding force of the chest wall
Palv=Patoms
What happens when the volume in the chest cavity is less than the FRC?
Forces favouring elastic collapse are low and forces on the chest favour expansion
Overall system wants to expand
What happens when the volume in the chest cavity is more than FRC?
Forces favouring elastic collapse are high and forces on the chest favouring expansion are high
Overall the system wants to collapse
What are the two components of elastic recoil in the lungs?
- Anatomical component: Elastic nature of cells and extracellular matrix
- Surface tension: generates elastic recoil at air fluid interfaces
What is surface tension?
Occurs at air water interfaces
- differences in forces on water molecules at this interface, surface tension develops
How is surface tension calculated?
Laplaces equation
- P=2T/r
Why is surfactant required in the lungs?
As explained in Laplaces equation - smaller alveoli are of a higher pressure than larger alveoli meaning air would move down the pressure gradient cause the small alveoli to collapse
- It reduces surface tension on the alveoli
How is surfactant produced?
By type II pneumocytes
What is surfactant composed of?
Lipids and proteins
- 30-40% DPPC
- 30-45% other phospholipids
- 5-10% protein (SP-A, B, C and D)
- Cholesterols
What is the role of the protein SP-A in formation of surfactant?
It is water soluble and has a role in innate immunity
What is the role of the protein SP-B in formation of surfactant?
Lipid soluble and speeds up formation of monolayer
What is the role of the protein SP-C in formation of surfactant?
Lipid soluble and speeds up formation of monolayer
What is the role of the protein SP-D in formation of surfactant?
Water soluble and has a role in innate immunity
What is the role of surfactant?
- Density of surfactant determines rate of alveolar inflation
- Decreases lung compliance
- Prevents oedema - reduces fluid entering alveoli
- Prevent over inflation
What factors determine air flow in the lungs?
Type of air flow
Resistance of the pathway
Pressure gradients generated across the airways
What is the relationship between airflow and the pressure gradient?
Proportional to each other
What is the relationship between airflow and the resistance?
Airflow is inversely proportional to the resistance
What are the three types of air flow?
Laminar flow
Turbulent flow
Transitional flow
What is laminar flow?
The steady flow sown a tube at uniform speed and direction
- Flow rate is maximal in the centre of the tube and reduces towards the edges
What is turbulent flow?
When the flow rate moves past a critical value and irregular currents (vortices) develop
- Greater pressure gradient is required to obtain the same flow as seen under laminar conditions
What is the relationship between gas movement and pressure difference under turbulent flow conditions?
Gas movement is proportional to the square root of the pressure difference
What is transitional flow?
In the airways there is a high number of bifurcations (branches) the flow is disrupted causing eddies
- Air flow changes between turbulent and laminar
How is air flow type determined?
Governed by Reynolds number
Re = (2radiusvelocity*density of gas)/viscosity
Re<1000 - Laminar flow
Re between 1000 and 1500 - Unstable flow
Re>1500 - Turbulent flow
Where in the airways is true laminar air flow shown and why?
Terminal part of the airways - by alveoli
- Because of velocity of air decreases and cross sectional area is high meaning Reynolds number will be as low as 10
Where in the airways is turbulent air flow shown and why?
Trachea
- Velocity of air very high
- Cross sectional area low
What is poiseuille’s law?
Determines the impact of resistance on airflow
Airway resistance is proportional to gas viscosity and the length of the tube but is inversely proportional to the fourth power of the radius
Does airway diameter have an impact on resistance?
yes big impact and hence flow rate
What is the airway resistance of a normal individual?
1.5cm H2O.s.litres-1
What contributes to airway resistance?
Pharynx - Larynx = 40%
Airways>2mm diameter = 40%
Airways <2mm diameter = 20%
What is the airway resistance of an individual with COPD?
5cm H20.s.litres-1
Wat contributes to airway resistance in a person with COPD?
Pharynx - Larynx = 12%
Airways>2mm diameter = 18%
Airways <2mm diameter = 70%
What factors impact airway resistance?
Mucas secretion - Reduce airway diameter
Oedema - Fluid retention - narrow airways
How does dynamic pressures allow for inspiration?
Interplural pressure becomes more negative (-5 to -15cm H2O)
Transmural pressure gradient decreases as it moves up from alveoli to trachea meaning that pressure increases to more than interplural pressure
Airways expand and airflow increases
How does dynamic pressures allow for expiration?
Interplural pressure increases to +10cm H2O
Transmural pressure +15 in alveoli and increases up the trachea
This makes positive pressure gradient from alveoli to atmosphere causing constriction and air to move out
Why do emphysema patients slow down their breathing?
Because the alveolar walls have broken down so have the risk of collapse
Slow breathing reduces the effect of dynamic pressures making airway collapsing less likely
- Also breath out through pursed lips to create a big resistance to slow airflow
How does lung volume affect airflow resistance?
- As lung volume decreases so does cross sectional area off airways causing increases resistance
- Dynamic pressure effect causes constriction of airways
- No matter how much effort required flow rate won’t increase
Why do patients with COPD struggle to exercise?
When there breathing rate increases they are not able to bring enough O2 before their next breath due to decreased lung volume
- Tidal volume decreases by as much as a half
- Not enough O2 to reach metabolic demands
How is the airway smooth muscle controlled?
Heavily dependant on GPCR cascades
- Gq pathway
- Gs pathway
- Gj pathway
Which GPCR cascade is responsible for the contraction of airway smooth muscle?
Gq pathway
How does the Gq pathway lead to contraction of airway smooth muscle?
- Activation if alpha q unit of membrane receptor
- Activates phospholipase C (PLC)
- Causes increased production of IP3
- IP3 activates receptors in calcium stores in the ER moving calcium into the cytoplasm
- Ca binds with calmodulin forming CaM complex
- This complex phosphorylates MLCK acting on myosin and causing contraction of smooth muscle
How does Gq pathway also stimulate cell growth?
When phospholipase C is activated it stimulates the breakdown of PIP2 and its conversion to diacylglycerol (DAG)
DAG stimulated protein kinase C
This stimulates cell growth
What receptors are involved in the Gq pathway?
- M3 muscarinic receptors
- H1 histamine receptors
- BK bradykinin receptors
How does the Gs pathway led to relaxation of the airway smooth muscle?
- Alpha s subunit is activated by GTP
- This stimulates adenylate cyclase producing CAMP
- Stimulates protein kinase A
- Protein kinase A phosphorylates IP3 receptor inhibiting it and therefore promoting relaxation
- Protein kinase A also phosphorylates MLCK reducing its action
- It also phosphorylates MLCP stimulating phosphatase promoting relaxation of muscle fibres
- Alpha s subunit interacts with K channels in membrane increasing the efflux of K+ causing hyperpolarisation
- This reduces Ca influx through voltage gated calcium channels promoting relaxation
What other effects does the Gs pathway have?
Reduction of gene activation an cell growth
How does protein kinase A promotes relaxation of airway smooth muscle in the Gs pathway?
- Phosphorylates IP3 receptor inhibiting its action
- Phosphorylates MLCK stopping it from phosphorylating myosin
- Phosphorylates MLCP promoting phosphatase, dephosphorylating myosin promoting relaxation
How does Alpha s subunit in the membrane promote relaxation of airway smooth muscle in the Gs pathway?
- Stimulates adenylate cyclase producing CAMP stimulating protein kinase A
- It also interacts with K channels in the membrane increasing the efflux of K+ causing hyperpolarisation reducing Ca influx through voltage gated calcium channels
What receptors are involved in the Gs pathway?
B2 adrenergic receptors
VIP receptors
What is the role of the Gi pathway in airway smooth muscle?
Oppose the action of the Gs pathway
How does the Gi pathway oppose relaxation in airway smooth muscle?
Activation of the Gi receptors inhibit adenylate cyclase stopping the production of CAMP and stimulation of protein kinase A
- Has a knock on effect which counteracts the stimulators effect of Gs activation
- Opposes the relaxation of smooth muscle
- Also inhibits BK channel
What receptors are involved in the Gi pathway?
M2 muscarinic receptors
How is the bronchial smooth muscle controlled?
Autonomic nervous system
- Parasympathetic and sympathetic
Humoral factors
- Epinephrine and histamine
What is the role of the parasympathetic nervous system in bronchial smooth muscle?
Acetyl choline released from postganglionic vagus nerve stimulating M3 muscaranic receptors on airway smooth muscle causing contraction by the activation of Gq pathway
What is the role of M2 receptors in the control of bronchial smooth muscle by the parasympathetic nervous system?
M2 receptors are present on the outer side of postganglionic nerve and are involved in a negative feedback loop
- When M2 receptors detect Ach, it stops it release
- Prevents overstimulation of airway
How does epinephrine control bronchial smooth muscle?
It is an agonist - leads to dilation of muscle
How does histamine control the bronchial smooth muscle?
Its released during the inflammatory process and leads to constriction
What is the role of the sympathetic nervous system in bronchial smooth muscle?
Releases norepinephrine stimulation B2 adrenoreceptor on airway smooth muscle
- Stimulates Gs pathway leading to relaxation
- It changes the sensitivity of IP3 receptor so not as much calcium leaves the store
What are the triggers for an asthma attack?
Atopic - Allergies, contact with inhaled allergens Non-atropic - Respiratory infections - Cold air - Stress - Exercise - Drugs
What occurs during an asthma attack?
Movement of inflammatory cells into the airways, release of inflammatory mediators such as histamine and subsequent bronchoconstriction
how can you tell if a patient has an obstructive lung disease such as asthma from a spirometer?
If the FEV1 is lower then 80% of the forced vital capacity
Overall vital capacity shouldn’t change
What is through to be the cause of asthma?
Hypersensitivity of parasympathetic activity
- Decrease in neuronal M2 function - negative feedback loop not working - over stimulation of airway smooth muscle
What does the antigen - challenge model show about the link between M2 receptors and Asthma?
- Change in M2 function is linked to eosinophils
- They cluster around nerve fibres and release major basic protein (MBP)
- MBP inhibited M2 receptors
What does the virus model show about the link between M2 receptors and Asthma?
Interferon causes down regulation of M2 gene expression
- hyperactivity of airway smooth muscle
What are the treatments for asthma?
B2 Adrenergic agonists - Salbutamol - short acting - Salmeterol with corticosteroids - long acting Anticholinergics - Block effects of Ach - Acts on M1 and M3 receptors - e.g.. tiotropium bromide Glucocorticoids - Anti inflammatory actions - e.g.. beclometasone - steroids
What is the central control of respiration?
Basic respiratory rhythm is controlled by centres in the medulla
Is breathing involuntary or voluntary?
Essentially it is involuntary but can be altered consciously
- Hyperventilation
- Breath holding
However these are overidden if required
What group is the dorsal respiratory group responsible for?
Quiet inspiration
Not quiet expiration as that is just elastic recoil
What group is the ventral respiratory group responsible for?
Control of forced expiration (requires extra muscle groups) and forced inspiration
What is the pre botzinger complex?
- Contains pace maker cells that are linked to control of breathing
- Located near the ventral respiratory group
- 12th cranial nerve (hypoglossal) sends inputs to diaphragm and muscles in chest wall to control inspiration
How do we know that the hypoglossal nerve is used in the pre botzinger complex?
Because when brain slice were took, electrodes showed spontaneous bursts of action potentials which match activity shown in hypoglossal nerve
What are the three types of breathing patterns generated from the pre botzinger complex?
- Eupneic - Normal breathing rhythm
- Sigh - increased level of activity - inhale more for a longer period of time
- Gasp - often seen in hypoxic conditions - ‘gasping for air’
How does the pre botzinger generate three different patterns?
All three patterns are generated from the same region of the brain and the same neurones but their inputs and modulation differs
What are the two types of cell in the pre botzinger complex?
Pacemaker cells and non pacemaker cells
What is seen in the activity of pacemaker cells?
- Regular spikes
- Bursts which are linked to contraction of the muscles - depolarisation and therefore inspiration
- A gap where cells depolarise and quiet expiration occurs (elastic recoil)
What is the NALCN?
Sodium leak channel
What is the importance of NALCN in the pre-botzinger complex?
- Contributes to the depolarisation phase
What occurs in a mutant NALCN knockout mouse compared to a wild type?
Breathing is irregular - mouse will stop breathing and then pant
The nerve recording show very little burst in mutant but normal spikes and burst in wild type
- Mimics what occurs in humans with CNS damage
What is the role of potassium in the pre-botzinger complex?
[K+] has an important effect on resting potential
- increase in extracellular [K+] increases bursting pattern
What are the two types of inward current responsible for bursting activity?
- The persistent sodium current ( INaP)
- CAN cation current (ICAN)
How are pacemaker cells classified?
- Neurones relying on ICAN for bursting are cadmium sensitive as cadmium blocks ICAN current
- Neurones relying on INaP for bursting are cadmium insensitive
What is the effect of hypoxia on the pre-botzinger complex?
- Decreased O2 available
- Cadmium sensitive bursting cells become inactive so rely on cadmium insensitive
- Leads to basic gasping pattern of breathing
What is the role of pneumotaxic centre?
Increases the rate by shortening inspirations - inhibitory effect on inspiratry centre
What is the role of apneustic centre?
Increases the depth and reduces the rate by prolonging inspiration - stimulates inspiratory centre
What is the Hering-Breuer reflex?
- Stops overinflation of the lungs
- Negative feedback loop
- Phrenic nerve causes contraction of diaphragm and lung inflation
- Stretch receptors in lung cause vagus nerve to inhibit inspiratory centre
What are the two types of chemoreceptors?
Central chemoreceptors
Peripheral chemoreceptors
What is the role of central chemoreceptors?
Monitors conditions in the cerebrospinal fluid sensing CO2 and pH
- Response to rise in CO2 so stimulation leads to ventilation
What is the role of peripheral chemoreceptors?
Located in the carotid body and aortic arch
- Respond to an increase in CO2 and decrease in pH and O2
- Stimulation leads to ventilation
What is the primary driving force for respiration?
CO2
What do drugs usually target?
- Receptors
- Enzymes
- Transporters/carriers
- Ion channels
What are receptors classified based on?
Structure, pharmacology and signalling
What does specify mean to do with drugs?
Receptors show specificity in the classes of drugs that they recognise - no drug is completely specific
Comment on the structure of receptors with a similar function
Structures are very similar but structure of the communication part (binding site) is slightly different - making finding specific drugs difficult
What are the four families of receptors?
- Ligand gated
- G protein coupled receptors
- Kinase linked receptors
- Nuclear receptors
What is required for a drug to produce a response?
Agonist + receptor —> Drug receptor complex —-> active drug receptor complex —-> Response
Its not enough for the drug and receptor to bind (affinity) it must also produce a conformational change (efficacy) causing a response
What is the difference between affinity and efficacy?
Efficacy induces a change that causes a response in the cell but affinity is just the likely hood that the drug and receptor will bind
How does affinity for a drug effect the dissociation rate?
High affinity for a drug means slow disassociation - dependant on structure of drug and receptor
What is the relationship between drug types and affinities?
No relationship between agonists and antagonists and affinity
Antagonists may have a higher affinity than agonists and other way round
What is occupancy?
Proportion of receptors occupied will vary with drug concentrations
How is occupancy calculated?
Number of receptors occupied/ total number of receptors
Varies between 0 and 1
How can occupancy be measured?
Radio ligand binding assays
- Response and occupancy is not directly proportional so cannot rely on response to measure it
How is radio ligand binding assays carried out?
- Prepare cells or membranes that contain protein of interest
- Aliquot out membranes onto filters
- Add radio label at different concentrations and equilibrate
- When equilibrated remove unbound drug by filtration
- Rinse
- Count radioactivity of filter
How is non specific binding in radio ligand binding assays dealt with?
- Most ligands bind non specifically to tissue, filter paper, glass ect
- Rinsing will not get rid of it all
- use two test tubes where one measures specific and nonspecific binding of radioactive drug and other just non specific binding
- Take them away from each other
What can cause non specific binding in radio ligand binding assays?
- Starting material not 100% pure - drugs may bind to unwanted proteins
- Drugs may enter fat (lipids) in plasma membrane
What characteristics must a radio ligand have?
- Must be biologically active
- Purity - e.g. no enantiomers
- Radioactive - labelling- very high specific activity to allow low concentrations
What are the two main choices of radio ligands?
- Tritium (3H)
- Iodine 125
What are the advantages of using tritium as a radio ligand?
- Labelled product indistinguishable from native compound
- High specific activities can be obtained
- Good stability
- Long half-life (12.5 years)
What are the disadvantages of using tritium as a radio ligand?
- Specialised labs required
- Labelling is expensive and difficult
What are the advantages of using iodine 125 as a radio ligand?
- If it has aromatic hydroxyl group can be incorporated at high specific activities
- Iodination east in most labs and cheap
What are the disadvantages of using iodine 125 as a radio ligand?
- More readily degraded
- Biological activity of ligand can be reduced
- Short half life (67 days)
What is the role of incubation in radio ligand binding assays?
To maintain the integrity of both ligands and binding sites
What should the protein concentrations be in a radio ligand binding assay?
Range of 0.1-1mg membrane potential/ml with assay volumes of 0.25-1ml
What is the role of additives in radio ligand binding assays?
Used to protect the tissue
Why must the temperature be controlled in a radio ligand binding assay?
Stop denaturation of receptor
Stop enzymes from breaking down proteins as they are usually contained in lysosomes but they will have been disrupted during the process
How are tissue+bound ligand and free ligands separated in radio ligand binding assays?
- Filtration or centrifugation
- In solubized receptors - dialysis, column chromatography and precipitation is used
What are the problems when separating tissue+bound ligand and free ligands in radio ligand binding assays?
The rate of dissociation of ligand receptor complex
- Lower affinity (higher KD) requires faster more efficient separation
What analysis is used on radio ligand binding assays?
Scatchard plot - shows:
- total bound
- Specific binding
- non specific binding
What scale is a scatchard plot plotted on?
Semi logarithmic scale - because if drug had a low affinity it could not be represented on a linear scale axis
Non specific binding only becomes a problem at a high concentration of ligand
What type of binding is saturable in radio ligand binding assays?
Specific - total number of receptors in the tissue is limited
Non specific is not saturable
What is The Langmuir Equation?
It describes the relationship between receptor occupancy, affinity and drug concentration
LR = RX/ X+KD
What is KD?
The dissociation constant - When 50% receptors are occupied by drugs the drug concentration is KD
What is the relationship between KD and affinity?
Low KD - High affinity
High KD - low affinity
What is EC50?
Effective concentration giving 50% of maximal response
- not 100% of receptors need to be occupied to give a maximum response (receptor reserve)
What is the ‘receptor reserve’?
Not 100% of the receptors are occupied to give a max response
Allows amplification of the signal
What is KD a measure of?
Affinity
What is the relationship between KD and EC50?
EC50 may be less than KD if we have less receptors
Why do binding and response curves differ?
- Because efficacy of agonist may influence size of response
- May activate multiple second messengers which would amplify the response
What is a limiting factor of response curves?
The machinery of response - e.g. used all the enzymes/2nd messengers
How is response calculated using a drug response graph?
Response = (Maximum response[X]^slope factor) / ([X]^slope factor + [EC50]^slope factor)
What does EC50 measure?
Agonist potency
- If a drug requires a small concentration to receive a high response it would have a high potency
On a drug response curve, where would the sigmoidal line be for a drug with a high potency be in relationship to others?
The sigmoidal line most left has the highest potency as a drug requires a small concentration to receive a high response
What does potency depend on?
Affinity efficacy and spare receptors
What is a partial agonist?
Partial agonists are not capable of achieving the full response
- Drugs may have the same EC50 but different maximal responses
What is the relationship between potency and partial agonists?
A partal agonist could be more potent even though it is a partial agonist - no effect
How do you know if a drug is a partial agonist?
Only by comparing the response to that of a full agonist
Why are partial agonists useful?
Because it doesn’t evoke a full response
- Less chance of overdose
- Much less desensitisation of receptors e.g.. B2 inhaler
- Easing of addiction
How can a partial agonist act as an antagonist?
The previously bound to receptors and the a full agonist is added
What is efficacy?
The measure of a single agonist-recepor complex’s ability to generate a full response
What properties determine the effect of a drug in a living system?
- Specificity
- Affinity
- Efficacy
What is specificity in relation to drugs?
The interaction with a structurally defined site/receptor
What is affinity in relationship to agonists and antagonists?
Ability to bind to a receptor
What is efficacy in relationship to agonists?
Ability to activate receptor
What is an inverse agonist?
Evokes a response opposite to that of a normal agonist
- Not an antagonist
- Has an efficacy below 0
- Cannot consume an active configuration
What can alter the efficacy?
GPRC’s may have allosteric sites which make it easier for the agonist to evoke a response
What type are most drugs used clinically?
Antagonists
Define antagonist
A drug that prevents the response of an agonist
What are the 5 different classes of antagonism?
- Chemical antagonism
- Pharmacokinetic agonist
- Physiological antagonism
- Non - competitive antagonism
- Competitive antagonism by receptor block
What is a chemical antagonism?
The substance combines in a solution so that the effects of the active drug is lost - agonist is chemically altered by the antagonist
Give an example of chemical antagonism
Adding a chelating agent (antagonist) to a heavy metal will inactivate toxicity
What are the two types of pharmacokinetic antagonism?
- Reduction in amount of drug absorbed
- Change in drug metabolism
Give an example of pharmacokinetic antagonism (reducing drug absorbed)
Opiate will reduce absorption in the GI tract
Give an example of pharmacokinetic antagonism (change in drug metabolism)
Antibiotics may lead to metabolism of warfarin for those patients taking it - problem
What is physiological antagonism?
The interaction of drug with opposing actions in the body
Give an example of physical antagonism?
Noradrenaline raises arterial blood pressure by acting on the heart and peripheral blood vessels - while histamine lowers arterial pressure by causing vasodilation
What is non competitive antagonism?
Blocks some step in the process between receptor activation and response - does not compete with agonist for the receptor site
Give an example of non competitive antagonism?
Smooth muscle interfering with gated Ca2+ channel which is required to bind to MLCK to contract - doesn’t directly block channel non competitive
What is competitive antagonism?
Competing with agonist for for binding site on a receptor
- Similar structure
- Does not create a response
Give an example of reversal competitive antagonism?
Effects of atropine on response to acetylcholine for guinea pig ileum
What happens to a dose response curve when a reversible competitive antagonist?
Sigmoidal shape moves to right- more conc required for max response
- EC50 increases
What is the dose ratio?
How many more times agonist is needed in the presence of an antagonist
How do you calculate dose ratio?
[Concentration of agonist in presence of antagonist] / [Conecentration of agonist in absence of antagonist]
What is schild analysis?
Measure antagonist affinity
How can you calculate dose ration from a schild plot?
Dose ratio = (conc of antagonist (Xd) / antagonist affinity constant (KD)) +1
What does PA2 value imply?
Higher the number higher the affinity
What are irreversible competitive antagonists?
Cannot be reversed by washing of the tissue
- Irreversible antagonism is time dependant
Give an example of the irreversible competitive antagonists?
The effects of the alkylating drug dibenamine on histamine responses in the guinea pig ileum
How does the drug become present in every cell?
- Absorption
- Distribution
- Metabolism
- Excretion
What is the role of diffusion in distribution of drugs through the body?
Drug crosses the plasma membrane to travel between cells
What factors effect whether a drug can diffuse through a lipid?
The physiological properties of the drug and if it is non polar
How do physiochemical properties of a drug effect whether it can diffuse through lipid?
Lipid solubility partition coefficient
- Measure of how easily the drug will dissolve into the lipid/aqueous phase
How does the polarity of a drug effect whether it can diffuse through lipid?
Non polar molecules dissolve through lipids freely
- Increasing rate of absorption from gut, penetration into brain and renal elimination
What are the characteristics of the intravenous route of drug administration?
- Straight into plasma (fastest way)
- Avoids metabolism
- Quick in emergency situation
- Not convenient
What are the characteristics of the intramuscular route of drug administration?
- e.g.insulin
- Speed of effect depends on muscle
- Short delay getting into plasma
What are the characteristics of the intrathecal route of drug administration?
- Inject into spinal cord - effects CNS
- eg. epidural
What are the characteristics of the inhalation route of drug administration?
- Gas
- Potential route if the target is in the lungs e.g. inhaler (salbutamol)
What are the characteristics of the oral route of drug administration?
- Most widely used route
- Pass through the gut into plasma through diffusion within the intestines
- Rate depends on gut contents
- Drug capsules used to alter rate of absorption
What is bioavailability?
Fraction of injected drug/fraction in plasma
What are the characteristics of the rectal route of drug administration?
- Through the gut
- Used in paediatric medicine
- also when local target
What are the characteristics of the percutaneous route of drug administration?
- Though the skin e.g. patches
- Can be used for when condition is in the skin
What factors effect drug absorption?
- Method of administration
- Molecular weight
- Lipid solubility
- pH and ionisation
How does pH and ionisation effect drug absorption?
Most drugs are weak acids
- be a salt so easily made into a tablet
- Will be in its undissociated from in stomach acid so can easily pass though membranes as its not charged
How does the pKa of a weak acid drug show how easily it will pass through the membranes using aspirin as an example?
pKa = pH +log(HA/A-)
When the dissociation of he drug is HA H+ + A-
- In stomach acid (pH 3), aspirin (pKa=3.5):
3. 2 = (HA/A-) meaning three times more of the drug is in its uncharged form so can pass through the membrane - In plasma (pH 7.4) - more drug in dissociated from so will stay in blood circulating the body
- In kidney (pH 8) favours dissociated form so will be trapped and excreted
Why would a weak base be used as a drug?
In poisoning situations
- Increases pH of plasma by sodium bicarbonate causing weak acid to be trapped an excreted
When does pKa=pH?
When 50% molecule is in its dissociated form
What regulated drug access to CNS?
Blood brain barrier
How does the blood brain barrow regulate drug access to the CNS?
Endothelial cells lining blood vessels in CNS form tight junctions impermeable to water soluble molecules
Lipid soluble molecules e.g. ethanol cross it easily
Tight junctions become laky during inflammation
What part of the CNS has a sparse blood brain barrier?
The chemoreceptor trigger zone
Give an example how the chemoreceptor trigger zone causes problems in drug effectiveness?
The chemoreceptor trigger zone is rich in dopamine receptors so when drugs fro Parkinson’s disease are added nausea is caused
- to stop this you have to co administrate a drug that inhibits the dopamine receptors in the chemoreceptor trigger zone
- It only inhibits those dopamine receptors as the drug has a large structure so cannot surpass the blood brain barrier in most if the CNS but can in the trigger zone as the blood brain barrier is sparse
What characteristic does a drug that needs to pass the CNS need to have and what is the disadvantage of this?
High solubility
- However means it can easily enter body fat
- Making dosage more difficult to calculate
What are the two reactions required for drug metabolism in the liver?
Phase 1 - catabolic reactions
Phase 2 - synthetic reactions
What occurs in the phase 1 creation of drug metabolism?
Catabolic reactions
- made more active to increase its size using microsomal enzymes such as cytochrome p450, alcohol dehydrogenase, MAO
- to allow it to pass the plasma membrane
What occurs in the phase 2 creation of drug metabolism?
Synthetic reaction
- Involve conjugation to produce an inactive product
What are pro drugs?
The active form of the drug isn’t released until after metabolism
- Slows doen rate of response
- Can be useful in avoiding symptoms like tiredness
How is aspirin eliminated from the body?
- Enters liver cells
- Encounters cytochrome enzyme which swaps the acetyl group for a hydroxyl group
- Conjugate into a larger molecule decreasing its access to tissues
- Cant interact with its target
- Excretion is promoted
How can drug metabolism be increased?
By adding inducers of P450 (an enzyme involved in drug metabolism)
Why do expectant mothers have to be careful what drugs they take?
Because spree rugs are distributed and trapped in the milk meaning it could be passed on to the baby
What is the time course of clearance for a single dosage of drug?
Follows a memo-exponential decay
- t-half value is the amount go time for the concentration to decrease by half
- Rate of elimination may very even if the drugs are of the same concentration targeting the same receptors
- t - half is not directly proportional to the concentration
What parts of the heart are involved in the spread of electrical activity?
Nodal cells
Conducting cells
Muscle cells
Connections – intercalated discs
Give overview of excitation in the heart
- Initiated at sino-atrial node
- Conduction to atria and atrioventricular node and then atrioventricular ring
- Passage through bundle of his
- Purkinjie system distribution to ventricular muscle cells
What is the size of the Sino atrial node?
15mm x 5mm x 2mm
Where is the sinoatrial node located?
The posterior aspect of the heart
- Junction between superior vena cava and right atrium
What is the speed of conduction of the sinoatrial node?
0.05m/s
What is the speed of conduction of the sinoatrial node via the atrial myocardium?
1m/s
this is the pathway that allows spread of electrical activity from right atria to left
Where does the electrical activity of the sinoatrial node spread?
To atrioventricular node and left atrium
What is the size of the atrioventricular node?
22mm x 10mm x 3mm
Where is the AV node located?
Posterior aspect
- Right side interatrial septum
What are the three sub zones of the AV node?
AN, N, NV
What is the speed of conduction through the AV node?
Slow concussion through AN-N= 0.05m/s
What is the role of the delay caused by the AV node?
Allow atrial contraction to finish
What is AV refractoriness?
Prevents excess ventricular contraction
It increases at higher heart rate to allow the hart to move maximum amount of blood and therefore CO2
What is the speed of conduction at the bundle of his?
1m/s
What is the speed of conduction at purkinje fibres?
4m/s
What is the speed of conduction at the ventricular muscle?
1m/s
Why do the ventricles contract in a spiral pattern?
Squeeze maximum amount of blood out
Describe the action potential for the Sinoatrial and atrioventricular node?
Gradual and slow depolarisation of the membrane
Which of the hearts nodes are dominant?
Sinoatrial node
- The atrioventricular node had the ability to take over for the sinoatrial node if it fails
What is the absolute resting potential for the atrial and ventricular muscle?
-80mv
How do cardiac muscle and nodal action potentials differ?
The muscle have a plateau phase in order to sustain contraction of the atria and ventricles
Why would summation of action potentials in cardiac cells cause problems?
Would never allow the ventricles to actually contract so cardiac muscle cannot fire another action potential until first is completely done
What parts of the heart can also act as pacemaker cells?
AV node and purkinje fibres
Describe the action potential of a pacemaker cell in the heart?
Slow depolarisation, fast depolarisation and fast repolarisation
What is the If current (funny current)?
- A cation channel with a Nernst of 0
- K+ channels are closed from the last action potential
- Hyperpolarition induced - so inactive when vm is positive
What causes the fast depolarisation of pacemaker cells in the heart?
When vm goes over -40mv
- Ca2+ channels open
- Peaks at 0mv
What causes the fast repolarisation of pacemaker cells in the heart?
- Ca2+ channels close and K+ open
- Shifts the membrane potential towards that of Nernst for K+
How is heart pacemaker action potentials regulated?
Innervation, temperature and by other pacemakers
How are the hearts pacemaker cells controlled?
Parasympathetic - ACh released from vagus nerve causes hyper polarisation and decreased pre potential slope Sympathetic - Noradrenaline released - Increase the prepotential slope - Increase the firing rate
Describe the cardiac muscle action potential
Fast depolarisation - Na+ channels open (shifts membrane potential towards Nernst for Na+) - Na+ close and Ca2+ open Spike - Leakage of some K+ channels Plateau - Ca2+ channels balance with K+ as Ca2+ tries to drive it positive and K+ negative Repolarisation - Ca2+ channels close - Ca2+ is transported out - K+ open and moves in
What is the purpose of the effective refractory period in the heart?
Due to the Na+ channels
Before they can become activating again, they have to go from open to inactive to closed
- Stops summation
What is the purpose of the relative refractory period in the heart?
- Stimulus to get action potential must be higher as membrane is still slightly hyper polarised
- Stops summation
On an ECG what happens between Q and T?
Start of ventricular depolarisation to repolarisation
Name sone inherited cardiac ion channel syndromes?
Short and long QT syndromes
How would the ECG of someone with long and short QT syndrome compare to a normal one?
Short QT - distance between Q and T is smaller - Repolarisation is accelerated Long QT - distance between Q and T is larger - Repolarisation is slower
How can ventricular action potentials be used to diagnose long and short QT syndrome?
Normal - 0.36 s
Long - >0.45 s
Short - <0.34 s
Some pathologies only show variety QT interval when exercising
What are the implications of long and short term QTs?
- Triggered activity
- Re entrant excitation
How do cardiac channelopathies cause triggered activity and what does that lead to?
Long QT
- Na+ channels may be closed and ready to be active and therefore open to early
- Generates another action potential causing a ectopic beat
- Ventricular tachycardia
- Ventricular fibrillation
What is ventricular fibrillation?
Lack of control of the heart
How do cardiac channelopathies cause re-entrant excitation and what does that lead to?
- Different layers of cells are impacted
- Trigger of electrical activity but not in all of the ventricular muscle
- Spatial and temporal dispersion of refractory period - extra electrical activity at certain parts of the muscle and at certain times
- Leads to ventricular tachycardia
- Ventricular fibrillation
What are the symptoms of long QT syndrome?
- Fainting
- Palpitations
- Sudden death
- Torsades de points on ECG
When does long QT syndrome onset?
Teen years
When are effects of long QT syndrome more likely?
When exercising or jumping into cold water
What are torsades de points?
Seen on an ECG - loss of coordination
How common is long QT syndrome?
1:10000 to 1:150000
What is the most common types of long QT syndrome?
LQT1 -Loss of function in Iks channel - 30-35% of cases LQT@ - loss of function in Ikr channel - 25-30%
What type o f long QT syndrome is similar to LQT1?
LQT5
- Loss of function in MinK
- 1%
What is LQT1?
Most common type of long QT syndrome
- K+ channel channelopathy
- Caused by a mutation in KV7.1
- Lots of mutations in transmembrane domains
- Loss of function
What is also associated with LQT1 and LQT5 long QT syndromes and why?
Deafness
- Due to Q1 k+ channel and its regulators E1 role in the ear
- In a E1 knockout mouse (MinK protein which is what is mutated in LQT5), there is no resigners membrane and no K+ rich endolymph meaning can’t hear
- Same in humans with these cardiac channelopathies
How does a gain of function in Na+ channels cause long QT syndrome?
- Na+ channels stay open
- Balance between anions and cations is lost
- Depolarisation lasts longer and repolarisation is delayed
- Long QT syndrome
How does a gain of function in Ca2+ channels cause long QT syndrome?
- Ca2+ channels dont close
- K+ channels can’t repolarise
- Repolarisation takes longer -
- Long Qt
How does a loss of function in K+ channels cause long QT syndrome?
- Not as much K+ leaves as quickly
- Repolarisation takes longer
- Long QT
What are the treatments for long QT syndromes?
B blockers
- Atenolol - B1 selective antagonist - slows down heart as has chronotrophic and ionotrophic actions but can’t be used if asthmatic as causes bronchoconstriction
What are the symptoms of short QT syndrome?
Arrhythmias, palpitations, fainting, sudden death
How many forms of short QT syndrome is there?
5
How many forms of long QT syndrome is there?
12
Who is short QT syndrome more prominent in?
75% males
- Onsets at late adolescence
What would an ECG of someone with short QT syndrome be like?
- Short/absent ST segment
- Tall T wave
- QT doesn’t vary when exercising - normal people it gets shorter
What are the 5 types of short QT syndromes?
- SQT1 - gain of function - K+ channel
- SQT2 - gain - K+
- SQT3 - gain - K+
- SQT4 - loss - Ca2+
- SQT5 - loss - Ca2+
How does a loss of function in Ca2+ cause short QT syndrome?
Loss of function in Ca2+
- Repolarise too quickly as Ca2+ cant enter to balance K+
How does a gain of function in K+ cause short QT syndrome?
Gain of function in K+
- K+ moves in to quickly
- Repolarisation to quick
What are the treatments for short QT syndromes?
Implant defibrillator
Define cardiac cycle
Mechanical and electrical events that repeat with every heartbeat
What are the four stages in the cardiac cycle?
- Inflow phase
- Isovolumetric contraction
- Outflow phase
- Isovolumetric relaxation
What is the middle of phase 1 of the cardiac cycle?
- AV valves open but little blood flows between atria and ventricles so ventricular pressure rises very slowly an approaches a plateau
- Pressure in atria also rise very slowly
Why is the end diastolic pressure less in the right ventricle then the left in the cardiac cycle?
Because the capillaries in the lungs are one cell thick and have lots of gap junctions so would rupture if the pressure was high
- would cause the lungs to fill with tissue fluid
What is the end of phase 1 of the cardiac cycle?
Atrial contraction
- After excitation contraction coupling, contraction of atria occurs and pushes the remaining blood into the ventricles
- <20% of the blood from atria is moved to atria in this phase
- Small rise in both chambers pressure
Why do the atrioventricular valves close in the cardiac cycle?
When the intraventricular pressure exceeds the atrial pressure
How is it ensured that the atrioventricular valves remain closed?
Ventricular contraction triggers contraction of the papillary muscles with their cordae tendinae that are attached to valve leaflets
- this tension prevents them from bulging back too far into the atria
What is the first heart sound?
Closure of the AV valves
- Split sound (0.04 secs) as mitral valve is slightly before tricuspid
What is phase 2 of the cardiac cycle?
Isovolumetric contraction
- Systole commences
- As ventricles contract, pressure in the ventricles exceeds the pressure in the atria causing the AV valves to shut
- Means ventricles are contracting with all the valves shut so that the pressure is increasing but the volume is staying the same causing a rapid increase in ventricular pressure
- Pressure rises above the pressure in the aorta/pulmonary valve causing aortic/pulmonary valves to open
What is phase 3 of the cardiac cycle?
As aortic valves open, the pressure in the ventricles and aorta rise and this is followed by a fall in ventricular volume
- Decrease in ventricular pressure becomes less rapid
- 50ml blood remains in the ventricles
When is maximal outflow velocity reached in the cardiac cycle?
Early in Phase 3 (ejection)
Maximal aortic and pulmonary artery pressures are also achieved
Are their any sounds in phase 3 of the cardiac cycle?
No because during ejection the opening of healthy valves are silent
When do the AV valves open in the cardiac cycle?
First part of phase 1
What causes the second heart sound?
Intraventricular pressures fall causing the aortic and pulmonic valves close abruptly
What causes the dichotic notch in the aortic and pulmonary artery pressure tracings?
When the aortic and pulmonary valves close it cases small back flow of blood into the ventricles
What occurs in phase 4 of the cardiac cycle?
Isovolumetric relaxation
- Blood flow across aortic/pulmonary valve becomes very slow so blood starts to flow backwards causing the aortic/pulmonary valve to close and blood continues o move forwards (dicrotic notch)
- Both valves are closed so pressure falls and the volume stays the same
What is lusitropy?
The rate of relaxation of the muscle fibres - rate of pressure decline in ventricles is determined by this
What is responsible for regulating lusitropy?
The sarcoplasmic reticulum
- responsible for re sequestering calcium following contraction
Why do the volumes of blood in the ventricles not change in isovolumetric relaxation of the heart?
Because all the valves close
- Volume doesn’t change but pressure decreases
What is the end systolic volume?
The volume of blood left in the ventricles after systole
- usually around 50ml
What volumes in the cardiac cycle represents the stroke volume?
The difference between the end diastolic volume and the end systolic volume
- Usually around 70ml
Why is there blood left in the ventricles?
So when start exercising, the cardiac output can increase immediately
Why does the left atrial pressure continue to rise after systole?
Because of venous return from the lungs
- The peak at the end of the left atrial pressure line is termed v-wave (just before mitral valve open)
What occurs in the start of phase 1 of the cardiac cycle?
- When ventricular pressure falls below that in the atrium the AV valves opens causing rapid ventricular filling
- Ventricular pressure continues to fall in this phase as its still undergoing relaxation
What is the ‘third heart sound’ and when is it audible?
During rapid filling and it may represent the tensing of the chordate tendinae
- low pitched so is best heard using the bell of a stethoscope
Why does the rate of filling fall during late diastole?
As the ventricles fill, they become less complaint and the intraventricular pressures rise
- reduces pressure gradient across AV valves so slows filling
How much of ventricle filing occurs passively?
90%
- 90% of the filling occurs before atrial contraction
Give some examples of asynchrony in the heart?
- Right atria contracts before left
- Left ventricle before right
- Right ventricular ejection before left
What should the heart rate of newborn babies be?
70-190 bpm
What should the heart rate of children be?
70-130bpm
What should the heart rate of adults be?
60-100bpm
What should the heart rate of athletes be?
40-60bpm
How are action potentials transmitted in the myocardium?
T -tubules and intercalated discs rapidly transmit action potentials in the myocardium
Electrical excitation - muscle contraction
What is the sarcolemma?
Myocyte plasma membrane
How are transverse tubules formed?
Formed by thousands of invaginations and inward foldings of sarcolemma forming transverse tubules
What is the role of the transverse tubules in the sarcolemma?
Allows the action potential to stimulate all parts, deep into myocyte simultaneously
- Faster rate of contraction
What is the sarcoplasmic reticulum?
Fluid filled membranous sac surrounding each myofibril
- Ca2+ store
In a relaxed muscle (myocardium) what are the concentrations of Ca2+ in the sarcoplasmic reticulum?
Sarcoplasmic [Ca2+] is low = 0.1 micro molar
Ca2+ pumps moved Ca2+ from sarcoplasm to sarcoplasmic reticulum = [10 micro molar]
What is the role of calsequestrin in the relaxed muscle?
Present in sarcoplasmic reticulum
- Binds ro Ca2+ to lower the [Ca2+] in sarcoplasmic reticulum so their is greater gradient and the pumps can work more efficiently
What is the role of the tropomyosin in a relaxed muscle?
It obscures the myosin/actin binding site preventing the myosin head from sticking to the actin molecule
Outline myocardium contraction
- Action potential propagates along transverse tubules
- Activate Ca2+ channels - Ca2+ diffuses out of SR into sarcoplasm
- Binds to troponin
- Conformational change in troponin/tropomysoin complex exposed myosin/actin binding site
- Myosin sticks to binding site
- ATP causes crossbruge cycling
- Muscle shortens
What is the relationship between muscle tension, number of crossbridges and sarcomere length?
Muscle tension should be proportional to no of crossbridges
Number of cross bridges proportional to sarcomere length
Why does short and long sarcomeres generate less muscle tension?
Short
- Overlapping thin filaments
Long
- Reduced areas for crossbridge formation
So there is an optimum sarcomere length
How can muscle length/tension relationship be measured?
Clamp a papillary muscle at specific length with a electrical stimulating electrode attached to a force transducer
- Record length of muscle
- Electrically twitch and record force
- change length of muscle
- repeat
What would the results of the length/muscle relationship test show?
- Short muscle - no force
- When length increases so does force
- 2.2 -2.6 micro meters - maximum response - free ti bind to any actin
- Too long - no force
How is the optimum sarcomere length in skeletal muscle ensured?
Joints
How is the optimum sarcomere length in cardiac muscle ensured?
Contained in mediastinum
- However only tissue keeping to from contracting to far so can expand to much under certain conditions
What is the Frank Starling mechanism?
The relationship between length and tension in muscle
What is the difference between isotonic and isometric contraction?
Isotonic - Muscle length changes and tension stays the same
Isometric - Length doesnt change
Why is the force velocity relationship more relevant than the length tension relationship in the heart?
Force velocity measure isotonic contraction which is what occurs in the heart
Length tension - isometric
What is contractility?
It is shown when an intact heart changes its output per beat when the end diastolic volume is constant
What are chronotropic effects?
Changes in rates
How can contractility change?
- When more cross bridges form per stimulus
- Dependant on the qualitative state of actin/myosin crossbridges
- Noradrenaline increases max force
What are changes in contractility known as?
Positive or negative inotropic effects
How does the frequency of beats effect contractility?
Increases contractility
How does the frequency of beats effect tension?
Increases tension
Also increases by an extra beat
Because of changes in Ca2+ availability
What is the Fink principle?
A way of measuring cardiac output
cardiac output = O2 uptake/ [o2]pv - [o2]pa
Can be measured using someones expired air
What methods can be used to measure cardiac output?
- Fink Principle
- Indicator dilution
- Thermodulation
- Ultrasound
What is the most commonly used method to measure cardiac output?
Thermodulation
- Cold saline injected into right atrium ad moves with blood
- Moves through system
- Sensor measures temp change in artery
- uses this and temp and volume of injection to calculate CO
What is the easiest way to measure cardiac output?
Ultrasound
- Measures real time changed in ventricular dimensions
- stroke volume calculated
- stroke volume x heart rate = cardiac output
What is the typical stroke volume?
80ml
What is the typical cardiac output?
5.5L per min at 69bpm
What is the typical cardiac index?
2.5-3.6L/min/m2
What is cardiac index?
Cardiac output/body surface area
What daily control cardiac output?
- Stroke volume
- Heart rate
- Innervation
- Intrinsic and extrinsic control
What are the two types of intrinsic control of cardiac output?
Homeometric
Heterometric
What is heterometric control of cardiac output?
The end diastolic volume is regulated by venous return influenced by - Blood volume (increase) - Vascular storage (decrease) - Muscle pump action - Vascular resistance - Atrial sucking - Gravity - Inspiration
What is homeometric control of cardiac output?
Positive inotropic effects
- Treppe law - strength of contraction increases as heart rate does
What are the two types of extrinsic control of cardiac output?
Autonomous nervous system
Humoral factors
How does the parasympathetic nervous system control cardiac output?
- Primary way of decreasing heart rate
- ACh onto SA node - decrease slope taking longer to reach threshold - action potential propagation slower
- Decreases heart rate, contractility and force per breath
How does the sympathetic nervous system control cardiac output?
- Speeds up heart and contractility
- Noradrenaline increases rate
What drugs are used to decrease heart rate through sympathetic nervous system?
B blockers
- Propanalol/atenolol
What type of cardiac control is dominant at rest?
Parasympathetic
What humoral factors are used in cardiac output control?
Thyroid hormone
- Increase heart rate when hyperthyroid
Insulin - increase in inotropic effects
Where is the main place of resistance?
In the arterials and small veins
- where blood first meets high resistance
What is poiseuilles law?
R = 8hl/πr^4
What does poiseuilles law show?
That any change in diameter will have a large impact on the resistance and in the calculation the radius is to the power of 4
What is the critical closing pressure?
Tissue pressure will collapse vessels if blood pressure falls
Whats the law of Laplace?
Transmural pressure = tension/radius
The smaller the diameter of the tube, the greater the transmural pressure
What are the consequences associated with collapsing vessels due to the law of Laplace?
Aneurysms
- Increases size, becomes easier to inflate, transmural pressure will decrease and the aneurysm will burst
What is compliance?
Compliance = delta v/ delta P
Why are veins known as compliance vessels?
They are more complaint then artiest meaning that blood tends to accumulate in venous side
- At rest 54% of blood will be the venous system
Why does post mortem blood pooling occur?
Blood tends to stay at the bottom of body if person dies on their back
What is the Windkessel effect?
The further away from the heart the pulsatile (pumping) nature isn’t as strong
Pressure is stored in the vessels to ensure flow is continuous
What is the difference between laminar and turbulent blood flow?
Laminar moves slowly and turbulent is when laminar flows interfere with each other because pressure is to high
What does Reynolds number show?
Measures the type of flow
<2000 = laminar
< 3000 = turbulent
Where is turbulent flow useful?
In the respiratory system
Why does turbulent flow not occur in the capillaries?
Because only one red blood cell fits along the capillaries so don’t interfere with each other
Why don’t you want laminar flow in the ventricles?
Would cause blood clots
- Stopped by papillary muscles and trabeculae carneae
What are the consequences of turbulent flow in the heart?
Could cause red blood cells to burst or become damaged
- why red blood cells are constantly replaced
How much of the total blood volume is in the capillaries?
5%
What is responsible for directing the flow in capillaries?
Pre - capillary sphincters
When is tissue fluid formed?
When the hydrostatic pressure is higher than the osmotic pressure so the plasma is pushed through gap junctions into capillaries into tissues
What is the role of osmotic pressure?
To push fluid back into the capillaries
What does formation of tissue fluid depend on?
Balance between hydrostatic pressure and osmotic pressure
How is tissue fluid drained?
By the limbic system
- Absorbs tissue fluid and is drained bak into right subclavian vein - superior vena cave - right atrium
What effect does increased blood pressure have on tissue fluid formation?
Increases tissue fluid as balance between hydrostatic and osmotic pressures is lost
- leads to oedemas
What effect does malnutrition have on tissue fluid formation?
Lowers the amount of protein in blood
- Can’t produce high osmotic pressure so hydrostatic erasure outweighs out
- Increased tissue fluid formation
- People with malnutrition tend to have swollen belly due to excess tissue fluid
Why is an oedema on the brain particularly dangerous?
Because skull can’t expand to decrease the pressure
What is the effect of histamine on tissue fluid formation?
Increases
- Makes capillaries leaky
What is an exercise oedema?
Increases permeability of vessels in active muscles
- increases hydrostatic pressure - increase up to 25%
What are the layers of large arteries?
- Endothelium
- Basement membrane
- Tunica media
- Tunica externa
- Need to have their own blood supply but medium and small don’t
Why do veins have one way valves?
To push the blood up towards the heart - stop gravity
Where in the body do veins not have valves?
Head and neck
What is myogenic regulation of of the circulation?
Contraction to prevent expansion of the artery
How is the circulation regulate by metabolic regulation?
By CO2/ pH
e.g. in an exercising muscle - produced CO2, pH change, temperature - vasodilates vessels to increase flow and remove CO2 and lose heat through the skin
How does the autonomic nervous system control circulation?
Parasympathetic - adrenergic - constrict
Sympathetic - cholinergic - dilate
Why does the innervation of nerves vary in the sympathetic control of circulation?
Low innervation in brain - because it always needs oxygen
High innervation - skin - blood flow varies to muscle and skin (temperature)
What humeral agents are responsible for controlling circulation?
Adrenaline - Vasoconstriction of skin - Vasodilation skeletal muscle/ liver - eg. in flight or fight response Kinins - Bradykinin - vasodilation peptide Angiotensin II -Increase blood pressure
What local agents are responsible for control of the circulation?
- Prostaglandins
- Serotonin
- Histamine
- Endothelium derived relaxing fator - Nitric oxide - released by endothelium cells in response to ACh - Stimulates cGMP causes relaxation
How does viagra work?
Inhibits the breakdown of cGMP which causes relaxation
How does nitroglycerin cause control of circulation?
- Thought to be converted into Nitric oxide
- But actually increases diameter of venous system
- Reduces contractility
reduces o2 needed and reduces chest pains
What part of the brain is responsible for controlling circulation?
The medullary centres
- Cardioaccelatratory system - speeds up heart rate
- Cardioinhibitory system slows down heart rate
How are signals transported from the spinal cord to the heart by the medullary centres?
Spinal cord - Sympathetic chain - ganglia - cardiac nerve - heart
How does the local environment lead to control of the medullary centres?
- Repsond to changes in pH, pCO2, pO2
- Causes an increase in intracranial pressure - due to swelling after brain injury - leads to a fall in blood flow to the brain
What is the crushing reflex?
Leads to an increase in vasoconstriction and blood pressure but causes bradycardia
Risk of death is high
How do peripheral proprioreceptors control the medullary centres?
Baroreceptors - stretch receptors
- Carotid sinus detect high pressure
- Causes atria, left ventricle and pulmonary veins low pressure
- High blood volume
- Release ANP
- Inhibition water uptake into kidney to control blood pressure
Buffer nerves
- Changes cardiac output to ensure blood pressure stables
- Glossopharyngeal and vagus nerves
- Short term regulation
What is the Valsalva manoeuvre?
Forcible expiration against a closed glottice
- Increase in thoracic pressure and decrease in blood pressure
- Venous return then decreases
- Decrease in baroreceptor stimulation
- tachycardia
- Venous return increase
How do chemoreceptors control medullary centres?
Mainly invloed in respiration
Activation leads to an increase in blood pressure
Cardiac chemoreceptors cause angina pain
How do higher brain systems control the medullary centres?
Hypothalamus Cortex and limbic system - Used in emergency situations - Defence area - Thermoregulatory centres which cause vasodilation and vasoconstriction - Bradychardia hypotension
What is the criteria for hypertension?
Diastolic - Less than 85 - normal - 90 -104 mild hypertension - 105-114 - moderates - Greater than 114 - severe Systolic - Less than 140 normal - 140-159 - systolic hypertension - Greater than 160 - severe
What are the types of hypertension?
Essential hypertension - Risk factors but no clear cause - can effect anyone Secondary hypertension - Consequence of a clinical condition
What are the potential causes of essential hypertension?
- MABP is cardiac output x resistance
- Cardiac dysfunction - essential hypertension increase response to stress and catecholamines
- Vessel abnormalities - sympathetic nervous system abnormalities, muscle hypertrophy - changes in smooth muscle blood pressure
- Kidney dysfunction - Volume induced hypertension
What evidence is there that essential hypertension is caused by genes?
Correlated with relatives
- Twins vs non twins
- Varies with race - higher among African - Caribbean
What are the known environmental risk factors for essential hypertension?
- Diet and obesity
- Adoption of western lifestyle
- Salt intake
- Vitamin D deficiency
What percentage of essential hypertension is caused by genetic predisposition?
30-50%
Give a study into salt and essential hypertension
Human studies
- Reduced salt by 3g/day will decrease mean arterial blood pressure (MABP) by 5mm
- Equivalent to a drug therapy reduces strokes
- Must be NaCl not Na+ reduction
What causes secondary hypertension?
Renal disease - Nephron function impaired - Blood volume and blood pressure increases - More damage an kidney failure Renal artery stenosis - Narrowing - Renin production and blood pressure increase Pheochromocytomas - Chromaffin adrenaline increase, blood pressure increase Hormone imbalance - aldosterone increase - Blood pressure increase
What are the consequences of hypertension?
- Flushing, sweating, blurred vision
- Clinically described as
asymptomatic - Arteriosclerosis/ atherosclerosis
- Aneurysms
- Stroke
- Heart attack
- Retinal attack
What are the treatments for hypertension?
- Lose weight
- Exercise
- Diet - salt, alcohol, caffeine
- Stop smoking
- Relax
- Pharmacology
How is pharmacology used to treat hypertension?
Diuretics
- Increase Na+ and Cl- excretion
Sympatholytics
- alpha blockers - decrease CNS sympathetic output - relaxes smooth muscle
- B blockers - propranolol - decreae heart rate and contractility
Ca2+ Channel blockers
- Decrease cardiac contractility and vascular muscle
How is the renal angiotensin system used to treat hypertension?
- ACE inhibitors
- AG II receptor blockers
Why is the dual approach of treating hypertension good?
Diuretic and something else
- Better control
- e.g. ACE inhibitor and Ca2+ blocker
How many people does Cystic fibrosis effect?
1 in 2500
1 in 20 - carriers
Why are carriers cystic fibrosis asymptomatic?
Only require 20% protein function for normal function
Carriers have 50%
How does cystic fibrosis effect the airways?
Causes clogging and infection
How does cystic fibrosis effect the liver?
Blockage of bile ducts
- Found in 5% of patients
How does cystic fibrosis effect the pancreas?
Blockage of ducts
- prevents secretion of digestive enzymes
- Can be used to check for it at birth with a heel prick
- Treatment can be to give tablets with these enzymes in
- 65% of patients
How does cystic fibrosis effect the small intestine?
Obstructions due to thick content
- effects 10%
- known as meconium ileus
How does cystic fibrosis effect the skin?
Excess secretion of NaCl via sweat glands
How does cystic fibrosis effect the reproductive tract?
95% males are infertile
- Absence of vas deferens
Small number of females infertile
Give the characteristics of Cystic fibrosis transmembrane conductance (CFTR)
12 transmembrane domains
- Regulatory domains - sequence of amino acids that plays a role in regulating the closing of the channel - target for phosphorylation by protein kinase A
What is the role of NBD1 and NBD2 in CFTR?
Sequence of amino acids that bind nucleotides such as ATP - regulates opening and closing of the channel
How many mutations that can cause cystic fibrosis are there?
Over 1900
- In transmembrane domains
- In NBD1 and NBD2
- In intra ans extracellular loops
What is variable penetrance in cyclic fibrosis?
People with the same mutations have different symptoms
- Environmental factors - don’t follow treatment
- Genetic - Non conducting regions
What do mutations causing cystic fibrosis do to the CFTR protein?
- Effect its mRNA - can lead to truncation
- effect trafficking
- Processing
- Some effect more than one of these
What are the common mutations of cystic fibrosis?
F508 - 90% allelic frequency - Most severe G551d - 1-3% - In uk higher All others are less than 0.1%
What is the effect of cystic fibrosis on the lungs?
Mucus is thicker
Recurrent bacterial infections - antibiotic resistance
Inflammation - Impacts immune system - hypersensitive - over inflammation - damages lung tissue
- After each infection, parts of lung tissue is lost
- 70% of deaths
What is the role of Na+K+ ATPase in the upper airway epithelial cell?
On baslateral membrane
Pumps 3Na+ out in K+ in - creates driving force for Na+ to move in by NKCC1
What is the role of NKCC1 in the upper airway epithelial cell?
On basolateral membrane
- Moves Na+, 2Cl- and K+ into cell
- Uses electrochemical driving force
- Na+ and K+ recycle through the basolateral membrane
- Leads to high intracellular Cl-
What is the role of CFTR in the upper airway epithelial cell?
Cl- channel on apical membrane
Cl- is secreted
- Sets up driving force for Na+ and water to move from the basolateral side of the cell to the apical
What is the pericilliary layer and what is its function?
Layer of water, Na+ and Cl- over epithelial cells in the airways
Mucus sits on top of the layer
Cilia in the layer - as cilia beat, layer and mucus moves up to be swallowed
What is the role of ENaC in the upper airway epithelial cell?
On apical membrane
- Na+ into cell through ENaC
- Balance between this and Cl- secretion that deicides height of pericilliary layer
What is the pericilliary layer optimum height?
7μm
If height of layer disturbed then cilia don’t work
What is different in a cystic fibrosis airway compared to a normal one?
- CFTR missing/ non functional
- Usually CFTR surpasses ENaC slightly so it is hyperactive
- Causes pericilliary layer to be small
- Cilia are bent over so don’t beat - patients can’t clear their airways
How does the mutation in F508 lead to cystic fibrosis?
- Trafficking and processing mutation
- Causes the protein ti be misfolded meaning the cells checking system targets it for degradation
- If the protein actually made it to the membrane function would be relatively normal
Why is the allele for cystic fibrosis so high in society?
It provided protection against cholera
- Cells in colon have CFTR which determines the water content of faeces
- Enterotoxins activate CFTR and cause diarrhoea
- Cholera killed due to diarrhoea
- Carriers only had 50% of CFTR channels as everyone else so were more likely to survive
What are the treatments for cystic fibrosis?
Physiotherapy - Losen Mucks and cough it up Bronchodilator drugs - Expand airways Antibiotics Steroids Mucolytics - Break down mucus
How does gene therapy work as a treatment for cystic fibrosis?
- It causes the delivery of CFTR to the target cell - for mutations in F508 this would make a relatively normal function
- Problem is that it needs to repeat treatments as airways cell change often - expensive
What new approaches for treating cystic fibrosis are there?
Potentiators
- Increase the potential of CFTR channels which must be trafficked
- Normally the G551D mutation is a target for ivacaftor
Correctors
- Force mutatnt copies of CFTR into the membrane
Combinations of these methods are being looked at
Give a study into the use of ivacaftor as a treatment of cystic fibrosis?
Clinical trial
- Compared with a placebo group: Massive improvement in infections, weight loss over a long period of time
What leads to the production of an ECG?
Summation of cells depolarisation and repolarisation gives resultant vectors
Measurement of vectors produce on ECG
What is the difference between electrocardiograph and electrocardiogram?
Electrocardiograph - Machine
Electrocardiogram - Trace
Why can electrical activity of the heart be measured through the skin?
When cardiac impulse passes through the heart, the electrical current spreads to all the adjacent tissues surround the heart and even reach the skin - electrical potentials can be recorded
Where do the leads for an ECG go?
Standard limb leads
- Right and left arms
- Left leg
Produces einthovens triangle
What is the isoelectric point on an ECG?
At rest no net current flow toward any electrode so no deflections on the ECG
What does a current flow towards on electrode on an ECG lead to?
Net current flow towards an electrode cause an upward deflection on the recording
What is the difference between a cable and a lead on an ECG machine?
Cables join the surface self - adhesive electrodes are connected by cables to the ECG recorder machine
A lead is the tracing of the voltage difference and what is actually produced by ECG recorder
Which leads shows the biggest and smallest deflection?
Lead II
Lead I
Explain a normal ECG
Spread of electrical excitation through the heart
- Atria begin their depolarisation - small muscle so deflection is small
- Ventricular depolarisation begins at the apex - ventricles big so deflection big
- Repolarisation of the atria happen at the same time but masked by electrical activity of ventricular depolarisation
- Ventricular repolarisation
What is the P wave on an ECG?
Atrial depolarisation
What is the QRS wave on an ECG?
Ventricular depolarisation
What is the T wave on an ECG?
Ventricular repolarisation
What are the average lengths of the sections of the ECG?
PR 0.12-0.20
QRS 0.8-0.10
QT 0.40 - 0.43
ST 0.32
What does a high p wave amplitude on an ECG imply?
Atrial hypertrophy - more muscle mass more to depolarise bigger deflection
What does a low aptitude T on an ECG imply?
Ventricular hypoxia - not enough o2
What does a long ST interval imply?
Acute myocardial infarction
How does heart rate vary naturally?
Bradycardia and tachycardia
- Exercise from 65 to 180bpm
- Sinus arrhythmia - 15% increase on inspiration, 15% decrease on expiration
How can heart rate vary abnormally?
Non exercise tachycardia - 150-200bpm
Flutter - 200-300bpm
Fibrillation - 300bpm and irregular
What is a heart block?
Impairment of conducting pathways
Infarction, artery disease ect
What is first degree heart block?
Interruption somewhere between the SA and AV nodes
slowing SA – AV conduction
Causing an increased PR interval
What are the two types of second degree heart block?
Mobitz I
Mobitz II
What is Mobitz I?
Type of second degree heart block
- SA impulses fail to evoke QRS
- Progressive prolongation of the PR interval culminating in a non conducted P wave
- The PR interval is longest immediately before the dropped beat
- The PR interval is shortest immediately after the dropped beat
What is the Mobitz II?
Type od second degree heart block?
- Mobitz II is usually due to failure of conduction at the level of the His-Purkinje system (i.e. below the AV node).
- Mobitz II is more likely to be due to structural damage to the conducting system (e.g. infarction, fibrosis, necrosis).
- Patients typically have a pre-existing LBBB or bifascicular block, and the 2nd degree AV block is produced by intermittent failure of the remaining fascicle (“bilateral bundle-branch block”).
Why is Mobitz II known as an all or nothing phenomenon?
Unlike Mobitz I, which is produced by progressive fatigue of the AV nodal cells, Mobitz II is an “all or nothing” phenomenon whereby the His-Purkinje cells suddenly and unexpectedly fail to conduct a supraventricular impulse.
What is third degree heart block?
In complete heart block, there is complete absence of AV conduction – none of the supraventricular impulses are conducted to the ventricles.
‘Perfusing rhythm’ is maintained by a junctional or ventricular escape rhythm.
Alternatively, the patient may suffer ventricular standstill leading to syncope (if self-terminating) or sudden cardiac death (if prolonged).
Typically the patient will have severe bradycardia with independent atrial and ventricular rates, i.e. AV dissociation.
What are the consequences of first degree heart block?
Benign
- found in athletes
What are the consequences of second degree heart block?
Mobitz I
- Benign - in atheletes
Mobitz II
- May require pacing
What are the consequences of third degree heart block?
- Chamber contractions out of synchrony
- Atrial contraction against closed tricuspid
- Reduced perfusion - dizziness and syncope
What is a cannon wave?
Cannon wave’ in jugular vein- R atria contracting at same time as R ventricle so a pressure wave is sent back up the jugular veins. The external jugular vein can be seen pulsing.
What is the most common type of arrhythmia?
Atrial fibrillation
What is atrial fibrillation?
Abnormal heart rhythm- irregular, rapid beating of the atria
Starts with brief episodes abnormal rhythm which become longer even constant
What are the symptoms of atrial fibrillation?
Usually asymptomatic but AF is usually accompanied by symptoms related to a rapid heart rate. Rapid and irregular heart rates may be perceived as palpitations or exercise intolerance and occasionally may produce angina. Congestive symptoms such as shortness of breath or oedema of ankles.
What are the treatments of atrial fibrillation?
flecainide
beta-blockers, particularly sotalol
amiodarone
dronedarone(only for certain people)
What is circus movements?
Circus movement or re-entry
Electrical signal not completing the normal circuit, but rather an alternative circuit looping back upon itself rapidly.
Refractory muscle normally prevents re-excitation
If wave of excitation meets non-refractory tissue it will carry on
What are the main kind of non steroidal anti inflammatories (NSAIDs)?
Aspirin
Paracetamol
Ibuprofen
Where is aspirin acquired from?
bark of a willow tree
What is aspirin?
Acetyl salicylic acid
- Used to be just salicylic acid but adding the acetyl group reduces some of its side effects (damages stomach)
What is meant by the NSAIDs being paracrine?
Effect the activity of any cells within their range
What is the mechanism of action of NSAIDs?
Normally
- Phospholipase A converts phospholipid to arachidonate
- Cyclo oxygenase (cox) converts it to cyclic endoperoxides which leads to inflammatory responses
- Anti-inflammatories interfere with cyclo-oxygenase
Give an example of what happens when an NSAIDs blocks a prostaglandin?
- Prostaglandin E causes vasodilation - by blocking this, inflammation decreases
How do NSAIDs act as a painkiller?
- PGE2 causes more pain as receptors for it on pain receptors making surrounding more sensitive to pain - blocking this is a painkiller
What is the role of thromboxane?
Favours blood clotting
Why is the control of Tx2 important?
Favours blood clots
- Controlling them limits chances of strokes and blood clots
How do NSAIDs have an anti inflammatory function?
Decrease vasodilation and in turn oedemas
- but is ineffective against mediators that contribute to tissue damage associated with chronic inflammatory conditions
How do NSAIDs have an analgesic function?
Decreases production of prostaglandins which sensitises nociceptors (pain receptors) to inflammatory mediators e.g. bradykinin, serotonin
How do NSAIDs have an antipyretic function?
They lower raised temperatures
- Thermostat in the hypothalamus activated via IL-1 induced COX2 production of prostaglandin E (PGE)
Why is paracetamol a poor anti inflammatory?
Because mostly exerts its effects on CNS not PNS
What are the types of cyclooxygenase enzymes?
COX-1 - Found in all cells
COX-2 - Induced in the inflammatory cells
COX-3 - Variant of COX-1
Which cycoloygenase enzyme is the best to target by NSAIDs and why?
COX 2 because it is only induced in the immune response
If COX 1 is targeted - leads to side effects because it is always active and has roles in tissue homeostasis
What cyclo oxyeganse does paracetamol target?
COX 3
Does work on others but much less
What cyclo oxyeganse does aspirin target?
Inhibits COX 1 and 2
What is the structure of COX?
Made up of two identical subunits, each with two catalytic sites (peroxidase and cyclo oxygenase)
- Drugs restricting access of substrate effectively blocking it
How does aspirin work?
Binds covalently to a ser residue in COX preventing arachidonic acid from reaching COX site
Why is aspirin known as the suicide inhibitor?
Because it covalently bonds meaning the body has to completely resynthesises the COX enzyme, it doesn’t unbind
How can it be ensured that NSAIDs target COX 2 not COX 1?
In COX 1 there is isoleucine present in the channel but in COX 2 it is switched for valine
Valine is smaller meaning that the channel is bigger
Bigger molecules are therefore synthesised so that they will fir in COX 2 but not COX1
What are the side effects of NSAIDs?
- Prostaglandins inhibit acid secretion and protect mucosa in the gut - Dyspepsia, diarrhoea, nausea, vomiting, gastric bleeding, ulceration could be stopped by co-administration of misoprostol (PG analogue) may be protective
- Renal Function, PGs maintain renal blood flow – Renal failure
- Liver Damage – Paracetamol
- Bronchospasm asthma attacks, Skin Rashes
Why can paracetamol lead to liver damage?
It creates a dangerous intermediate during it’s metabolism
Only occurs in large excess of paracetamol or already impaired liver function
What are the advantages and disadvantages of COX 1 selective NSAIDs?
Ads
- Antithrombotic (stops blood clots)
Dis
- Gastrotoxicity
What are the advantages and disadvantages of COX 2 selective NSAIDs?
Ads
- Anti-inflammatory, analegestic, less side effects
Compare aspirin and paracetamol
Aspirin - Anti-platelet action - Reduced risk of colonic and rectal cancer - Reduced risk of Alzheimer’s - Weak acid, rapid and efficient absorption in the ileum Paracetamol Weak anti-inflammatory - COX-3 selective - Wellabsorbed, metabolized in liver - Less side-effects than aspirin with long term use, but large doses may increase kidney damage - N-acetyl-p-benzoquinone imine is hepatotoxic in uncongugated form - Competitive Inhibitor
What is rheumatoid arthritis?
Destruction of cartilage (joint swelling)
More common in women
Late onset
Increased risk of heart attacks and strokes
What are the causes of rheumatoid arthritis?
Not entirely clear
Genetic component
Environmental component eg. smoking
Why is rheumatoid arthritis considered an autoimmune disease?
Because it is caused by Th1 cells in the immune system
- Recruits macrophages which are involved in destruction of cartilage and bone
How does methotrexate folic acid act as a treatment for rheumatoid arthritis?
- Was originally an anticancer drug
- Has cytotoxic and immunosuppressant activity
- Inhibits activation of T helper cells -stopping its conversion into Th1 cells
- Limiting the production of cytokines that cause inflammatory response
- Usually, t helper cells recruit macrophages that release cytokines which cause inflammation
How do glucocorticoids act as a treatment for rheumatoid arthritis?
Work at the level of transcription to stop the production of these cytokines
How do biological drugs treat rheumatoid arthritis?
Directly interfere with cytokines actions and therefore reduce inflammation
What is the clinical use of ciclosporin?
Often used to stop rejection of transplants
Inhibit transcription of pro inflammatory cytokines
How does ciclosporin work?
Usually
- During the activation stage of T cells intracellular [Ca2+] increases
- This activates calcineurin - a phosphatase which targets the transcription factor NF kappa B (activates the immune cells and inflammatory response)
- Removal of phosphate of NF Kappa B allows it to move in nucleus and transcribe
- Ciclosporin binds to it and stops it from entering the nucleus
What is a consequence of using biological drugs to treat rheumatoid arthritis?
Causes immunosuppression so is more susceptible to infection
Name some new ideas for anti inflammatory drugs being researched?
- Antibodies being used to target cytokine itself - preventing it attaching to receptor
- Drugs that target IL1
- Mimic small soluble receptors for cytokines - mopping up free cytokines so cannot bind to its receptors
What is IL1?
Interleukin 1 - family of cytokines that contribute to rheumatoid arthritis
What are the advantages of using new drugs to treat rheumatoid arthritis?
Highly specific and effective
Depends on the cytokines the Individual releases
Long half life
Needs to be injected but one every 6 months
How many people suffer with asthma?
5.4 million in UK
1/5 households
What drugs are available for the treatment of asthma?
Bronchodilators - salbutamol
Anti inflammatory agents - glucocorticoids
What is the problem with using bronchodilators to treat asthma?
Polymorphisms in B2 adrenoreceptors associated with reduced efficacy of bronchodilators
How are allergies tested for?
Inject patients with a small amount of a known allergen and look for immediate ad late phase reactions
Outline IgE mediated hypersensitivity
IgE are a class of antibodies produces against allergen
- indviduals become sensitised (2-3 weeks)
- IgE antibodies bind tightly to IgE Fc receptors on mast cells basophils (mast cells in blood) and eosinophils
- Mast cells are designed to fight against parasites and recruit other immune cells
- In some people allergens pass through skin and mucous surface (due to illness)
- Mast cells confuse them for parasites - allergic reaction
What happens when an allergen binds to an IgE on a mast cell?
Release of histamine and prostaglandins
Causes the first phase of an asthma attack
What are the two stages in an asthma attack and how are they treated?
Intermediate - B2 inhaler
Late phase - Glucocorticoids
How many people have a late phase stage in an asthma attack?
50% of patients
What occurs during in the late phase reaction in an asthma attack?
- Activation of transcription factors e.g. NF Kappa B
- Controls the prodiuction of cytokines which attract other immune response to the tissue (in this case lungs)
- Leads to inflammation and tissue damage
What is the link between Th2 cells and asthma attacks?
Th2 - type of T helper cell Activates IL4 (type of cytokine) which is what produces IgE antibodies that cause the allergic problems
How do glucocorticoids treat asthma?
Work at the level of Th2 cells - limit production of IgE
- Effect mast cells and stop the release of cytokine
- Also work on eosinophils
What are the side effects of chronic steroid use?
- Easy bruising
- Poor wound healing
- Increased abdominal fat
- Cataracts
- Hypertension
What is the role of the glomerulus?
Filters plasmas
Allows H20 and small molecules through
Restricts the passage of blood cells and proteins
180l/day of filtrate
What are the layers in the filtration barrier?
Epithelial cells
Basement membrane
Endothelial cells
How do endothelial cells act apart of the filtration barrier?
They are flat cells with large nuclei
Make up the capillary wall
Circular fenestrations - gaps between them - allows filtrate to move through
How does the basement membrane act as part of the filtration barrier?
It is the main barrier Continuous Made of collagen, laminin, fibronectin Negatively charged Filters based shape, size and charge
How do epithelial cells (podocytes) act apart of the filtration barrier?
They have extensions form the cell body known as trabeculae. Coming off these are finger like protections called pedicles which crossover each other making pores for filtrate to move through
Why does charge effect filtration?
Basement membrane is negatively charged so will repeal negatively charged molecules - making it less likely for them to cross the barrier
What is Kf?
The filtration co efficient
What are the forces governing filtration?
Hydrostatic pressure in capillaries
Hydrostatic pressure in Bowman’s capsule
Oncotic pressure in capillaries
Oncotic pressure in Bowmans capsule
What is the equation to calculate glomerular filtration rate?
GFR = Kf (Hydrostatic in cap+Oncotic in bc)–(Hydrostatic in bc+Onoctoc in cap)
What is the single nephron filtration rate (SNGFR)?
50nl/min
Why doesn’t the hydrostatic pressure in Bowman’s capsule change much?
Volume in fluid in bowman capsule doesn’t change as it is constantly flowing and draining into the proximal tubule so hydrostatic pressure doesn’t really change
- 20mmHg
What is the oncotic pressure of Bowman’s Capsule?
0
Why is there always filtration in the glomerular capillaries?
In normal capilaries, half way along the over powering force swap but not in glomerular capillaries - this is to ensure filtration always occurs
What is the normal rate of glomerular filtration?
125ml/min
Why must there be regulation of GFR (auto regulation)?
Because arterial blood pressure effects the filtration rate so has to be maintained when the blood pressure changes
What is the auto regulatory range?
Between 80-200 mmHg the glomerular filtration rate is regulated so doesn’t really change
- The range when the body is capable of adapting to different blood pressures
Why does the filtration rate increase by the auto regulation?
Resistance in the afferent arteriole decreases, causes vasodilation
Renal blood flow goes up, hydrostatic pressure increases, filtration increases
Why does the filtration rate decrease by the auto regulation?
If vasoconstriction occurs in the afferent arteriole, less blood, renal flow decreases, hydrostatic pressure decreases and decrease in arterial blood pressure
What happens if there is an increase in arterial blood pressure within the auto regulatory range?
Increase in arterial blood pressure, increase in blood flow, increases GFR, auto regulation increases resistance in afferent arteriole, decrease in resistance blood renal flow and glomerular filtrate drops back down to normal level
What are the two theories to explain auto regulation?
Myogenic theory
Tubuloglomerular feedback theory
What is myogenic theory?
Detects change in blood pressure by smooth muscle in afferent arteriole
- When arterial blood pressure increases
- Stretch afferent arteriole
- Afferent arteriole constriction
- Increase afferent arteriole resistance
What is tubuloglomerular feedback theory?
Juxtaglomerular apparatus
- Macula densa cells detect the rate of flow in glomerular filtrate
- They can then release vasoactive chemicals to return the GFR back to normal
What is osmolality a measure of?
Concentration
How is osmolality meausred?
= [X]*n
Where n = the number of particles x dissociates into
Eg. 100mM NaCl
= 200mOsmol/kgH20
Why are mammals and birds the only animals to concentrate their urine?
Only ones with a loop of henle
How many nephrons drain into one collecting duct?
6
What are the main parts of the kidney involved in counter current manipulation?
Loop of henle
Collecting duct
Outline the process of counter current manipulation in determining urine concentration
- Interstitial fluid osmolality in the cortex starts at 290
- Cl- and Na+ are lost from the thick ascending limb causing the osmolality to change to 600 in the medulla
- This creates a driving force for the loss of water in the loop of henle making the osmolality of the interstitial fluid 1400
- This then makes driving force for loss of Cl- and Na+ again making osmolality 90 in thick ascending limb
- Change in osmolality in the cortical collecting duct to 290 drives water out making concentrated urine
Which parts of the loop of henle are permeable to water?
Ascending limb not permeable to water but is to Cl and Na
Descending limb is permeable to water but not to Na and Cl
How does vasopressin work?
Osmoreceptors detect a change in osmolality by +- 3mosmol/Kg Causes the release of vasopressin
- It is thought that vasopressin causes the insertion of aquaporin 2 channels into the apical membrane of the principle cell in the collecting duct. Aquaporin 3 and 4 on the basolateral membrane are not regulated by vasopressin meaning net increase in reabsorption of water
What is the transverse and vertical gradient hypothesis?
The driving force created by the loss of water and Na+ and Cl- - causing changes in the osmolality
The vertical gradient
- The osmolality decreases as you go down
- If you compare the gradients of the thick ascending and the thin ascending limb they are different
Where is aquaporin 1 found?
Thin descending limb
What happens in a human and mouse knockout of aquaporin 1?
Have problems with their urine concentration but other pathways compensate for it
What occurs in the thick ascending limb using the channel proteins?
Basolateral membrane
- Na+K+ATPase and a K+ channel - creates a strong electrochemical gradient (high Na+ and also strong positive charge)
- CLCK - assisted by Barttin an causes the net reabsorption of Cl-
Apical membrane
- NKCC2 - Transports Na+, 2Cl- and K+
- ROMK - Recycles K+ on apical
What happens if CLCK is not functional?
Bartters syndrome
- Genetic inheritence
- Salt wasting and Polyuria - can’t concentrate urine
- Hypokalemia
- Metabolic alkalosis
- Hypercalciuria
What occurs in the principle cell in the collecting duct?
Basolateral - Na+K+ATPase - gradient - Kir2.3 - K+ transport - Aquaprin 3 and 4 - always active to reabsorb water Apical - ENaC - Na+ channel into cell - ROMK - K+ out - Aquaporin 2 - active in the presents of vasopressin to reabsorb water
What is the role of urea in counter current manipulation?
When water is reabsorbed in the collecting duct the concentration of urea increases so creates a driving force for urea to diffuse out into the interstitial fluid
Some urea is reabsorbed back into the the thin ascending limb
What proteins are present for urea transport on the inner medullary collecting duct?
Basolateral
- UT-A3
Apical
- UT-A1
What occurs in an UT-A1/A3 knockout mouse?
When allowed water
- Osmolality of knockouts urine is half of wild type
When water deprived (osmolality should increase o conserve water)
- Knockouts stays the same but wild types doubles
Why must the kidneys have a special blood supply?
Because if it was a normal blood supply so that it wen from the cortex to the medulla and out then the H20 would be moved out and solutes in
What is the counter current exchange model?
That the kidneys specialise blood supply (the vasa recta) loops
- Goes from the cortex to the medulla and then back to the cortex
As plasma moves down ascending limb - driving forces (osmotic and conc) for H20 and solutes in
Moves to medulla and driving forces pus solutes back out and water back in
- Keeps osmolality the same
What is the role UT-B found on red blood cells?
Mediates the movement of urea in blood cells
What happens to patients with loss of function mutations in UT-B?
Struggle to concentrate their urine
- Counter current multiplication works but counter current exchange doesn’t
How is pH calculated?
pH = -log[H+]
What is the pH of plasma in the body?
Typically arterial end of tissue bed is 7.35 and venous is 7.45
What are the physiological effects of fluctuations in [H+]?
Excitability of muscle and nerve
Enzyme activities
K+ levels
What are the average pH values around the body?
Gastric secretions - 0.7 pH units
Cerebrospinal fluid - 7.3
Pancreatic secretions - 8.1
Final urine - 5.4
What are the sources of acid/alkali in the body?
Metabolism: Large amounts acid - 15 moles/day of CO2 (lungs) - 40 mmol/day net H+ - Western diet an excess of H+ Diet: Alkali (fruit ) and acid in food 20 mmol/day H+ Loss base: 10 mmol/day OH- Net excess 70 mmol/day H+
What systems are involved in controlling acid/base balance?
- Blood and tissue buffers – seconds
- Respiration – minutes
- Renal – hours/days - only mechanism for extrusion (add/remove) where as the others only minimise
Where are buffers present?
Blood
Extracellular fluid
Intracellular fluid
Urine
Give some examples of buffers?
Haemoglobin
HCO3-
Inorganic phosphate
Weak acids/bases on proteins
Wat is the primary extracellular buffer?
Bicarbonate
What is the equilibrium equation that determines pH bases on Co2 and H+ concentration?
CO2+H2O H2CO3 H+ +HCO3
How does bicarbonate act as buffer according to the following equation?
CO2+H2O H2CO3 H+ + HCO3
Increase in CO2
- Will bind with water to form biarbonate which will dissociate into H+ and HCO3
- Increase pH
Increase in H+ ions
- Will bind with HCO3 forming H2CO3 and dissociate into CO2 and H2O
- Decrease in pH
What is the Henderson - Hasselbalch equation?
pH = pK + log [HCO3]/[H2CO3}
Where pK is a constant and at body temperature its 6.1
Normally [HCO3}/{CO2]
- 20:1
6.1 + log 20 = 6.1 +1.3 = 7.4
=> normal pH
If during a gas analysis a patient is seen to have a low pH and low [bicarbonate], what would they have?
Metabolic acidosis
If during a gas analysis a patient is seen to have a high pH and a high [bicarbonate], what would they have?
Metabolic alkalosis
If during a gas analysis a patient is seen to have a low pH and high [bicarbonate], what would they have?
Respiratory alkalosis
- Suggests problems with the lungs
If during a gas analysis a patient is seen to have a high pH and high [bicarbonate], what would they have?
Respiratory acidosis
- Suggests problems with the lungs
Where are peripheral chemoreceptors found?
Carotid and aortic bodies
What is the main stimulus for peripheral chemoreceptors?
Hypoxia - Fall in pO2 in presence of low oxygen
What is the role of the glomus cells in peripheral chemoreceptors?
Glomus cells depolarise and fire action potentials which go to nerves and signal the respiratory system to change rate
What is the structure of a carotid body?
Small - 2mg
40 times more blood going through chemoreceptors than brain
High metabolic rate
Glomus cells
Type II cells - supporting role
Have sympathetic and parasympathetic inputs
What is the mechanism for peripheral chemoreceptors?
- A decrease in pO2, pH or an increase in pCO2 causes inhibition of BK K channels
- Causing depolarisation of glomus cell and an action potential is fired
- Causes Ca channels to open
- Increase Cai
- Causes the release of neurotransmitters (Act, dopamine, NA, 5-HT, substance P and ANP)
- Causes stimulation of afferent nerve fibres
What is the main activator of central chemoreceptors?
Hypercapnia
- High CO2
Where are central chemoreceptors found?
Within the brain parenchyma, ventrolateral medulla and other brain stem nuclei
- Bathed brain in extracellular fluid
- Separated from arterial blood by blood brain barrier
What is the significance of the blood brain barrier separating the chemoreceptors from the blood?
It has poor ion permeability
- Doesn’t allow H+ to cross
- But does allow CO2 - causes acidosis of the brain extracellular fluid - stimulates chemoreceptors
Why are there more buffers in the blood then brain?
So that the pH change there will be greater than in the blood so that central chemoreceptors will be activated
Would a metabolic or a respiratory disorder effect the pH of the brain extracellular fluid more?
Respiratory
- Because metabolic changes ion concentration of the blood but this can’t pass the brain blood barrier due to its low permeability
What are the two types of neurones in central chemoreceptors?
- Acid activated - activated by serotonin
- Acid inhibited - activated by GABA
How are chemoreceptors though to be related to babies that die of sudden infant death syndrome?
They are believed to be lacked acid activated neurones so can’t regulate their blood pH well enough
How do the peripheral and central chemoreceptors respond differently to a respiratory acidosis?
Both respond
- Peripheral respond first
- Central will be responsible for 65-80% of the drive to change the pH because the o2 levels will be normal - which is the main drive for peripheral
How do the peripheral and central chemoreceptors respond differently to a metabolic acidosis?
Peripheral have an acute repsonse and central a longer term role
Will cause severe hyperventilation in an attempt to decrease the pCO2 - this will cause the hydrogen ions to decrease and therefore raise the pH
How can we voluntary change our pH?
Hyperventalte
- decrease in CO2, decrease in H+ and increase pH
- Cause mild alkalosis
Slow breathing
- High CO2, Increase in H+ and decrease in pH
- Cause mild acidosis
What are the three mechanisms in which the kidneys control the bodies pH?
HCO3- handling
Urine acidification
Ammonia synthesis
Where does HCO3- handling occur?
90% in the proximal tubule
10% in the distal tubule
What is the mechanism for HCO3- handling?
Basolateral
- Na+K+ATPase creates a electrochemical driving force for Na+
- Na+ HCO3- cotransporter
Apical
- H2CO3 filtered from proximal tubule and dissociates into H2O and CO2
- CO2 diffuses through
- H20 moves in through aquaporin 1
- These combine forming carbonic acid - dissociates unto H+ and HCO3-
- H+ is recycled back out the apical membrane via the Na+H+ exchanger
- HCO3 moves out basolateral - net reabsorption
What are the two types of base conservation that occurs in the kidneys?
Acidification of urine - 25%
Ammonia synthesis - 75%
What happens during urine acidification?
Start with an alkaline salt and convert it to an acid salt
e.g. Na2HPO2 —-> NaH2PO4
What is the mechanism for urine acidification?
Na2HPO4- loses a Na+ through Na+H+ exchanger
The H+ goes to the NaHPO4- to form NaH2PO4
- This H+ comes from the dissociation of H2CO3 inside the cell -HCO3- net reabsorbed
Where does urine acidification occur?
Doesn’t necessarily have to be the proximal tubule
- Anywhere in the nephron where there is a Na+H+ exchange
What is the mechanism for ammonium production in the kidney to change pH?
Diffusion trapping
- Ammonia diffuses out of the cells and is added to H+ to form NH4+
- NH3 formed by the conversion of Glutamate to alpha keto glutamate as it loses NH3 and H+
- H+ diffuses out of the Na+H+ exchanger
What occurs in acidosis?
- Increase in H+ excretion
- Normal HCO3- excretion
- Decrease in urine pH
- Increase in plasma pH
What occurs in alkalosis?
- Decrease in H+ excretion
- Increase in HCO3- excretion
- Increase in urine pH
- Decrease in plasma pH
What are the causes of respiratory acidosis?
Decrease in CO2 elimination
- seen in lung disease, emphysema, chronic bronchitis
- Leads to high CO2, low pH and HCO3
How can respiratory acidosis overcome by the body?
Lungs not functioning properly so can't be fixed by respiration Fixed at the level of the kidney - Increases secretion of H+ - Increases reabsorption HCO3- - Rises pH but causes further rise HCO3-
What is the cause of respiratory alkalosis?
CO2 elimination is high
Caused by ventilation due to fear stress or pain
How can respiratory alkalosis overcome by the body?
Lungs not functioning properly so can't be fixed by respiration Fixed at the level of the kidney - Decrease in secretion of H+ - Decrease in reabsorption HCO3- - lowers pH but causes fall in HCO3-
What are the causes of metabolic acidosis?
Ingestion of acid
Loss of alkaline fluid - diarrhoea, cholera, diabetic ketoacidosis
How is metabolic acidosis overcome by the body?
Respiratory compensation - Increased respiratory rate - increase in pH and drop in CO2 Renal correction - Increased secretion H+ - Increased reabsorption HCO3-
What causes metabolic alkalosis?
Ingestion of alkaline fluid
Loss of acid
Vomiting - increase in pH and HCO3-
How is metabolic alkalosis overcome by the body?
Respiratory compensation
- decrease in respiratory rate
- decrease in pH and rise in CO2
Kidney doesn’t not help - not understood why
What is a mixed disorder?
More than one primary disorder
eg. respiratory acidosis and metabolic acidosis
What is the worst combination of mixed disorder?
Both same type e.g. Respiratory acidosis and metabolic acidosis
Because the pH add together do is life threatening
Give an example of a life treating mixed disorder
Asthma
- Cant get enough CO2 out so respiratory acidosis
- Anaerobic respiration occurs due to lack of O2 so lactic acid is formed - metabolic acidosis
Give examples of mild mixed disorders
Alcoholics
- Metabolic acidosis - breakdown of alcohol
- Metabolic alkalosis - vomiting
COPD
- Respiratory acidosis - can’t get CO2 out
- Diuretics - metabolic alkalosis promotes loss of H+
Salicylate Poisoning
-Respiratory alkalosis
- Metabolic acidosis
What type of disease is Liddle’s syndrome?
Gain of function
Autosomal dominant
What are the symptoms of Liddle’s syndrome?
Na+ retention Fluid retention Hypertension Hypokalaemia Metabolic alkalosis Low renin and aldostrerin levels
What causes Liddle’s syndrome?
Mutation in ENaC channel which is found on the apical membrane of an epithelial cell
- Mutation is in the proline rich motifs in the beta or gamma subunit of ENaC
- This is responsible for tagging the protein for endocytosis
- This means that ENaC is not removed so Na+ reabsorption is too high and therefore so is water reabsorption
Give the characteristics of the ENaC channel?
Made of three subunits: alpha, beta and gamma
In a 1:1:1
Can transport a small amount of Na+ with just alpha but requires all three for normal function
What was seen in a Liddles mutant xenopus oocyte compared to the wild type?
Much higher amount of Na+ channels opening
Bigger current meaning more Na+ transport - double the current of that of the wild type
Why does Liddle’s syndrome lead to hypokalaemia?
(Low plasma K+)
- The more Na+ reabsorbed then the more K+ that is recycled across the apical membrane through ROMK as Na+ is exchanged for K+ on the basolateral
How does Liddle’s syndrome lead to metabolic alkalosis?
- Na+ is possibly charged so if that leaves the cell then it will leave a negative charge
- Forming a large transepitheial potential
- Creates a big driving force for H+ excretion causing metabloic alkalosis
How does Liddle’s syndrome lead hypertension?
Hypertension will lead to low renin and aldosterone which in a normal person would lead to ENaC being removed from the apical membrane of the principle cell to stop Na+ and therefore water reabsorption to lower blood pressure
- However, in a Liddle’s person the ENaC channels cannot be removed as the domain that targets it for endocytosis is mutated
- Therefore Na+ and Water + reabsorption does not decrease
- Hypertension persists
What is the treatment for Liddle’s syndrome and how does it work?
Amiloride
- Blocks ENaC channels and therefore stops reabsorption of Na+
Why does Spironolactone not work as a treatment for Liddle’s syndrome?
Usually works as an antagonist against aldosterone
Ineffective in Liddle’s as aldosterone doesn’t really have an effect
What are the symptoms of diabetes insipidus?
Polyuria
Polydipsia (thirst)
Dehydration - serious
How common is diabetes insipidus?
1:25,000
What is primary polydipsia diabetes insipidus?
Massive suppression of vasopressin production
Excessive H2O intake
What is is gestational diabetes insipidus?
Found in pregnant women
- Placenta produces enzymes that break down vasopressin
- Managed by controlling fluid intake
- Goes back to normal after birth
What causes central diabetes insipidus?
Impaired vasopressin production
- Acquired - Infection, Head trauma, Surgery
- Congenial - Neurohypophyseal D1 mutation, 67 mutations found and anyone of them cause them, some of the mutations cause problems in the trafficking of vasopressin from the hypothalamus to the posterior pituitary
What are the causes of nephrogenic diabetes insipidus?
Impaired effect of vasopressin
Acquired - more common
- Lithium disrupts vasopressin system - bipolar treatment
- Some antibiotics, antifungals
- Hypokalaemia and hypercalciuria
- Acute or chronic renal failure
Congenital
- Mutation sin ACPR2 (vasopressin receptor) x linked
- Mutation in AQP2 gene - impact trafficking (dominant) or function (recessive)
What are the symptoms of nephrogenic diabetes insipidus in infants?
Hypernatrimic dehydration
Poor feeding
Skin dryness
Depressed anterior fontanel - soft spot on babies head
What are the treatments for central diabetes insipidus?
Desmopressin
- Nasal spray
- Agonist
What are the treatments for nephrogenic diabetes insipidus?
Difficult to treat
- Possibilites are modulator drugs which work when proteins are misfiled but would still be functional if got to the membrane
- When misfolded they are sent for degradation instead
- These drugs take them to where they need to go instead
What were the first general anaesthetics and who discovered them?
Nitrous oxide - Horace Wells Ether - William Morton Chloroform - Simpson - stole it from graduate student Robert Glover
What are the types of general anaesthetic?
Chemical - Inhalation - Intravenous Physical (not commonly used in medicine) - Hypothermia
What types of intravenous general aesthetics are there and provide an example?
Halogenated hydrocarbons - Isoflurane Barbiturates - Thiopential Steroids - Alphahexane
What is a MAC value?
The minimal alveolar concentration to abolish response in 50% of patients to surgical incision
What does the MAC and lipid solubility graph show about general anaesthetics?
That there is a relationship between lipid solubilty and its potency
- Nitrous oxide requires a large volume to admit a response so is safe
- Halothene - only requires a small volume
What is lipid theory in relation to general anaesthetics?
It was thought that the drug entered the plasma membrane and it undergoes lipid expansion causing the membrane to be more fluid in the CNS
What were supported and disagreed with lipid theory in relation to general aesthetics?
Pros
- Relationship between lipid solubility and potency
- No relationship between structures of the drugs
Cons
- Temperature effect - If lower temperature then the membrane became more solid even though it acts as a physical anaesthetic
-Binding was saturable - suggesting that there is a protein binding site
What is the protein theory in relation to general anaesthetics?
General anaesthetics can associate with GABAa receptors in the central nervous system
How was the mechanism of action of general anaesthetics discovered?
Mutagenises of proteins that were thought to be targets for the anaesthetics
What receptor do general aesthetics target?
GABAa - receptor for GABA - most common inhibitory protein in the CNS
What subunits of GABAa do volatile general aesthetics target?
alpha and beta
What subunits of GABAa do intravenous general aesthetics target?
beta
Why were the lipid theory and protein theory confused in relation to general aesthetics?
Because the binding sites are deep within the protein and to gain access to the set they must enter the plasma membrane - explains the relationship between lipid solubility and potency
What are the effects of low concentrations of general aesthetics on neurotransmission?
Synaptic transmission to CNS decreases
- Reticular formation effected causes patient to become unconscious
- Effects on hippocampus - short term amnesia
- Thalamic sensory relay nuclei parts of complex - analgesia (pain dulling)
- Some volatile also inhibit spinal reflexes
What are the effects of high concentrations of general aesthetics on neurotransmission?
Effects all areas of brain function
- Loss of motor control, reflexes, respiration and autonomic regulation
What are the four stages of anaesthesia?
- Analgesia
- Reduces response to pain - Excitement
- Dangerous
- Unconscious
- Reflexes are exaggerated and breathing becomes erratic - Surgical anaestheisa
- Unconscious
- Breathing regular
- Loss of response to painful stimuli
- Short term amnesia - Medullary paralysis
- Central regulation of cardiovascular is lost
- death
What is the ideal general anaesthetic?
Rapid induction Loss of consciousness Analgesia Muscle relaxation Rapid recovery Avoid stages 2 and 4
Give some example of intravenous anaesthetics
Propofol
Thiopental
Etomidate
What are the advantages and disadvantages of intravenous anaesthetics?
Advantages - Easy to administer - Rapid induction - Propofol has rapid metabolism, good for induction of anaesthesia - Rapid recovery Disadvantages - May hide on body fat - difficult to maintain level of anaesthesia - Painful at site of injection - Respiratory depression - Cardiovascular depression
Why are both intravenous and inhaled anaesthetics used in surgery?
The intravenous injection leads to patient being unconscious
- Conc falls quickly so another injection would have to be administered in order to keep the patient asleep
- After the patient is unconscious an inhaled anaesthetic is used to maintain the level as its easily controlled
Give some example of inhaled anaesthetics?
Nitrous Oxide, Isoflurane, Desflurane, Sevoflurane
Why is it a problem if a patient had damaged lungs when using inhaled anaesthetics?
Because the only route of entry/exit is via the lungs
How can malignant hyperthermia be triggered by general anaesthetics?
If patient has a specific mutation
- Can be triggered by halogenated general anaesthetics
- Ca2+ quickly moves out of ER which activated mitochondria to quickly produce lots of ATP and lead to muscle contraction
- Uses all available O2 so little available for other parts of the body
- Can lead to death
How can malignant hyperthermia triggering by general anaesthetics be treated?
By administrating a drug to block this receptor causing it before using the anaesthetic
What are the effects of ketamine as a general anaesthetic?
Powerful analgesia Amnesia Sensory loss Hallucinations Involuntary movements Irrational behaviour on recovery
How is the depth of an inhaled anaesthetic determined?
Concentration of drug in inspired gas - less lipid soluble - father equilibrium
Pulmonary ventilation
- Increase rate of ventilation to increase rate at which a change occurs in the concentration in blood brain barrier
What is episodic ataxia?
Irregular, uncontrolled muscle contractions
- occurs in less than 1 in 100000
- At least 6 types
- Type I and II are more understood and affect more people
What are the characteristics for type 1 ataxia?
Autosomal dominant Onset 10-20 years Ataxia, dizziness Brief attacks Caused by a mutation in KCNA1
What are the characteristics for type 2 ataxia?
Autosomal dominant
Onset child to teens
Ataxia, vertigo, nausea, headache
Attacks can be 30 mins to 24 hours
What are the general symptoms of ataxia?
Trunk instability Vertigo Vomiting Dizziness Nystagmus Nausea Headache Visual blurring
What is the trigger for episodic ataxia type I?
Physical or emotional stress, vestibular system, abrupt change position
How does the mutation in KCNA1 lead to episodic ataxia type 1?
Loss of function mutation
- found in the cerebellum and neuromuscular junction
- Causes a decrease in the voltage from it
- Will cause a delay of repolarisation in neurones in the cerebellum
- Role of the cerebellum is to coordinate groups of muscles
- If signal isn’t normal then loss of this coordination
What are the treatments for episodic ataxia type 1?
Acetazolomide - Carbonic anhydrase inhibitor - Changes the pH of body fluid and therefore lower the excitatory of cerebellar cells Carbamazpine and phenytoin - Na+ channel blockers
What are the triggers for episodic ataxia type II?
Physical or emotional stress
Describe the mutations in CACNA1A that cause episodic ataxia type II?
Many different point mutations
Mutation is usually around one of the poor in the protein - not exclusive
Mostly truncation mutations
What disorders are related to mutations in CACNA1A?
Familial hemiplegic migraine - Mis-sense mutations Spinocerebellar ataxia type 6 – repeat expansion C terminus Episodic ataxia type II - Point mutations
Different mutations in CACNA1A cause different disorders, what does this show?
Mutation position and type determines the phenotype
Where id the CACNA1A protein located?
Purkinje cells
Granule cells
Cell bodies central neurones
How does mutations in CACNA1A lead to the symptoms of episodic ataxia type II?
Mutation in CaV then struggle to release neurotransmitters which will control movement in skeletal muscle
What does a CACNA1A knockout show?
- Up to 10 days normal (mimic episodic ataxia type II in humans as doesn’t onset until teens)
- After 10 days balance problems
- Ataxia
- Falls with twisting movements
- Death 3-4 weeks after birth (more severe then human condition - maybe because completely knockout out where as in humans its just mutated)
Outline an experiments findings that explain how CACNA1A mutations lead to ataxia?
The current through the wild type and mutant Ca channels were measured using barium
- Results were normalised as the current was divided by the max current recorded
- The peak current in the mutant channel was slightly more positive meaning the membrane will have to depolarise by another 8mv before it opens
- Takes slightly longer
- This reduced Ca2+ influx
- Stops neurotransmitter release
- Problems with control of skeletal muscle
What are the treatments for episodic ataxia type II?
Acetazolomide
- Carbonic anhydrase inhibitor
- Changes the pH of body fluid and therefore lower the excitatory of cerebellar cells
What are the characteristics of epilepsy?
- Seizures
- Episodic neuronal discharges
- 0.5-1% population
- The areas of the brain affected determine symptoms
- Can be caused by inheritance, brain trauma, infection, tumours
How is epilepsy sub categorised?
Partial simple - part of brain with no loss of consciousness
Generalised simple
Partial complex
Generalised complex - most of brain and loss of consciousness - most severe
How do acquired changes in ion channels cause epilepsy?
Changes ion channels in response to damage
Autoimmune diseases
How do inherited changes in ion channels cause epilepsy?
Due o balance between inhibitory and excitatory neurones
- If too much activity in excitatory - neuronal discharge - seizure
- If not enough activity in inhibitory - neuronal discharge - seizures
What is the role of voltage gates Na+ channels in neurones?
Depolarisation
What is the role of voltage gates K+ channels in neurones?
Repolarisation
What is the role of voltage gates Cav channels in neurones?
Neurotransmitter release
What is the role of AchR channels in a neurone?
Post synaptic membrane activation
What is the role of GABA receptors in a neurone?
Post synaptic membrane inhibition
What is the role of HCN channels in a neurone
Hyperpolarisation - activate cyclic nucleotide gated channel
What is the role of the Nav1.1 channel?
It is a voltage gated Na channel that mediates the regulation of inhibitory neurones. It activates the Cav channel triggering the release of ACh which binds to the GABA receptors on the post synaptic membrane of the excitatory neurone causing inhibition
What is the structure of Nav1.1 channel?
24 transmembrane domains
4 pores
What kind of mutations in Nav1.1 can cause epilepsy?
Loads of different mutations
Can be missense or truncation
Different types of mutations lead to different types of epilepsy
What occurred in a Nav1.1 +/- knockout mouse?
50% of Nav1.1 channels - compared currents of that and wild type
- Wild type has lots of action potentials
- Mutant - action potential firing is reduced and gets worse as experiments on
Why does a loss of function in Nav1.1 lead to epilepsy?
Means less action potentials fired from inhibitory neurone - less GABA released so GABA receptors on excitatory neurones are not activated - depolarisation of excitatory neurone as there is less suppression - increased risk of firing an action potential as resting potential is lowered - seizures
Why is there some scientific confusion over mutations in Nav1.1 and epilepsy?
Because there are also gain of function mutations which also cause epilepsy
Does a missense or a truncation mutation in Nav1.1 cause a more severe form of epilepsy?
Truncation
What is a febrile seizure?
Body temperature rises very quickly in children and triggers a seizure
How do mutations in GABA receptors lead to epilepsy?
Loss of function mutation
- Causes an increase excitatory output due to loss of inhibition
How do mutations in AchR lead to epilepsy?
Gain of function mutation
- Causes increased excitatory output due to excessive AchR activity so requires less Ach
How do mutations in Nav1.2 lead to epilepsy?
Gain of function mutation
- Causes increased excitatory output
What is the role of HCN and Kv7.2 channels?
Don’t play a role in production of action potential but change the rate of firing
- Change the resting potential in a way that will increase/decrease the rate
How does a mutation in HCN or Kv7.2 channels lead to epilepsy?
Loss of function mutations
- Causes increased excitatory output due to loss of firing control
Why do we have pain?
Pain is protective - to stop damage
What do loss of function mutations in Nav1.7 lead to?
Pain disorder
- loss of pain
- early death - could have an infection and wouldn’t know
What does a gain of function mutation in Nav1.7 lead to?
Pain disorder
- Enhanced pain - erythromelalgia
- Activated without nociceptor activation
- Burning pain, redness, heat
State an explanation for people having different pain thresholds
Suggestion is that polymorphisms in Nav1.7 channel may affect peoples sensitivity to pain
What is generalised anxiety?
No clear reason or focus symptoms interfere with normal productive behaviour
What are the types of anxiety?
Panic disorder
Phobias
Post-traumatic stress disorder
Obsessive compulsive disorder
What are the behavioural tests used on animal models for anxiety?
Elevated plus maze or cross
- Used with rodents
- One bar has is open and other has railings - would stay by railings so don’t fall off
- Is given an anxiolytic then would go on both sides equally
Light/dark box
- try to hide in the dark compartment
- with anti anxiety drugs - go into the light
What is the Galvanic Skin response?
Lie detector test but can also be used to test the effctiveness of anti anxiety drugs in humans
- Measure the conduction of the skin
- Conduction is measured better when skin is wet
- Sweat when anxious
What are GABAa receptors?
GABA ionotrophic receptor found on dendrites and somas of interneurones
GABA is the most common inhibitory neurotransmitter in the CNS
Cl- selective
What is an orthosteric site?
Agonist binding site
- Causes activation of ion channel
What antagonists are there for GABAa receptors?
Competitive
- Bicuculline
No competitive
- Picrotoxin - binds inside the channel
How many subunits does GABAa have?
5
- 2 alpha
- 2 beta
- 1 gamma
What is an inverse agonist for GABAa?
Beta carboline
- Stabelises the closed form of the receptor
- Can lead to seizures
Where does benzodizapene bind on GABAa?
Allosteric site
- found on the interface between alpha and gamma subunits
What is an allosteric site?
It modifies the activity of a receptor itself
- activation of the allosteric site does not activate the receptor - stops overdose of drugs
Why is benzodiazepine relatively safe?
Cant overdose
- Doesn’t activate GABAa receptors alone - needs the presence of GABA
What is meant by benzodiazepine being a positive allosteric regulator?
Enhances the response of GABAa receptors in the presence of GABA
What regulates GABAa receptors?
Barbiturates, neurosteriods, alcohol and some general anaesthetics
What is the role of GABAb receptors?
- Gi/o protein coupled receptor - Mediate slow transmission
- Pre-andPostsynaptic
- Inhibit voltage-gatedcalcium channels produces presynaptic inhibition
- Activate Potassium channels (GIRK) produce postsynaptic inhibition
Where are the GABA binding sites found on GABAa receptors?
Found between the two alpha and beta subunits
How can benzodiazepine cause death?
Summates with the action of other drugs e.g. ethanol
What do some GABA receptors not have allosteric binding sites for benzodiazepine?
Alpha 4 and 6 have a changed amino acid - histidine to threonine
Makes it not sensitive to benzodiazepine
What happens to a knock in mice (when changing the amino acid in GABAa receptor) when doing the light/dark box experiment?
Replace alpha 2 subunit to alpha 4 or 6 y changing the one amino acid
Mouse in light dark box won’t move into the light given benzodiazepine
What are the physiological effects of benzodiazepine?
Sedation/Anxiolytic
- decreased responsiveness to constant level of stimulation
Hypnosis
- latency of sleep onset is decreased, duration stage 2 (non-rem)
-sleep increased, duration of rem sleep decreased
Anterograde Amnesia
- Prevent memory of events experienced while under their influence eg. Flunitrazepam / “Rohypnol”
- Anti-convulsant
inhibit development and spread of epileptiform activity - Reduction of muscle tone
Give an example of how benzodiazepine acts as an allosteric regulator?
Current of GABAa receptor increases with presence of diazepam
When diazepam is washed out the current decreases again
How was the mechanism of benzodiazepine researched?
Single channel studies were conducted
How does benzodiazepine increase the action of GABAa receptors?
Increases the frequency of opening of the channel
Conductance is unaffected
What happens if you increase the concentration of bibiturates on GABAa receptors?
Starts to act as an agonist - causes channels to open
Why are bibiturates used in euthanasia?
Because when concentration increased they cause activation of all GABAa receptors in CNS- complete inhibition - CNS depression
How do benzodiazepines enter the CNS?
High lipid solubility
What does the drug half life depend on?
Dependant on renal function, age and other medications
Why is it advantageous for some benzodiazepines to have a shot half life?
When being used for insomnia
How does the half life of benzodiazepines used for generalise anxiety differ?
Long half life - lasts for days
e.g. when diazepam is metabolised it releases active intermediates
What are the adverse effects of benzodiazepine?
Sleepiness, impaired psychomotor function, amnesia
Addictive effects with other CNS depressants, fatal in overdose
Tolerance
Misuse
Physical dependence
Why are benzodiazepines considered relatively safe?
Because the highest benzodiazepines can go into is hypnosis - not coma because it is only an allosteric regulator of glutamate so can’t overdose
What happens with increases concentrations of barbiturates?
Barbiturates are also allosteric regulators of glutamate but with increasing concentration can become an agonist
What happens when benzodiazepines are mixed with alcohol?
Summates in the presence of other CNS depressants - can overdose
What can physical dependance on benzodiazepines lead to?
Withdrawal effects
- Increased anxiety, insomnia, CNS excitability, convulsions
What other drugs other than benzodiazepines can be used to treat anxiety?
Benzodiazepine partial agonists
Receptor selective benzodiazepine agonists - to remove unwanted side effects
Buspirone 5HT agonist
- effective in anti anxiety as well as antidepressants takes up to 6 weeks to feel effects
B adrenoreceptor antagonists
What is epilepsy?
Unprovoked seizures High frequency discharge by a group of neurones Focus Partial or generalised Diagnosis with an EEG
What are the causes of epilepsy?
Head injury - loss of neurones - initiation site for seizures Local lesions Tumours Infection Genetic causes - ion channel mutations
What is an absence seizure?
Found in children
- Do not lose consciousness but as if they switch off momentarily
- Mutation in voltage gated Na+ channels
What is the difference between partial and generalised seizures?
Generalised - all areas of the brain
Partial seizure - abnormal behaviour - only seen on one side on one side of the brain
What are the triggers of epilepsy?
Altered blood glucose
pH
Stress and fatigue
Flashing lights
What does a seizure trigger?
Apoptosis of neurones - slight brain death
What is status epileptics?
If a seizure lasts more than two minutes then it is considered a medical emergency
Will be given benzodiazepine
What are the main targets for anti-epileptic drugs?
Inhibitory synapse
- Target GABAa receptors
- Cause increase un GABA release
- GABA metabolism (enzymes that break down GABA)
Give examples of anti-epileptic drugs
Benzodiazepines
Barbiturates
Uptake inhibitors eg. tiagabine
Metabolic inhibitors eg. vigabatrin, valproate
What are the disadvantages of using barbiturates as treatments for epilepsy?
It has a low therapeutic index, causes sedation due to its complex pharmacokinetics
What are the mechanisms of action of valproate?
GAD enzyme converts glutamate into GABA
- Valproate increases GAD
It also uses epigenetic
How does valproate use epigenetics in its mechanism of action?
- histones that are methylanated represses transcription which can be reversed by DNA demethylase
- When DNA is acetylated it promotes transcription
- valproate favours acetylated form an promotes transcription of enzymes that convert glutamate to GABA
What is the mechanism of vigabatrin?
GABA is broken down by GABA transaminase
- vigabatrin irreversibly binds to it to stop GABA being broken down
- Suicide inhibitor
How are use dependant Na+ channel inhibitors selective?
Na+ channels go from open, closed to inactive before they can open again
These drugs stabilise Na+ channels in an inactive state so stops channels from opening so readily
- It only works on channels tat have been opened as if they are inactive them must have opened
Give some examples of Na+ channel inhibitors
Phenytoin
Carbamazepine
Lamatrigine
What channels are targeted to treat absence seizures?
T type Ca channels
e.g.. ethosuximide
GABApentin - acts on a subunit on voltage gated Ca2+ channels - not selective for T type Ca channels
Name some new drugs developed to treat epilepsy
Levetriacetam
- When associated with protein SV2A it some how decreases the amount of glutamate released from neurones
Felbamate
- Weak NMDA channel blocker
What is unipolar depression?
Mood swings always in same direction
- Reactive - response due to events that happen in their life (75%)
- Endogenous - can’t explpain why (25%)
What is bipolar disorder?
Patient oscillates between extreme excitement and a low mood
Mania can last for several weeks
What are the symptoms of depression?
Low mood (aledonia) Suicidal thoughts Irritability Loss of interest in daily activities insomnia/ excessive sleep Loss of appetite Cant concentrate Low self esteem
Who is depression more common in?
Women
What can depression lead to?
More likely to get cancers, cardiovascular problems
15-30% of untreated patients commit suicide
Which part of the brain is deep brain stimulation performed on as a treatment for depression?
Singular cortex and nucleus accumbens
How does the nucleus accumbens contribute to depression?
Part of the limbic system
- Causes an increase of BDNF in the brain when stimulated - relieves the symptoms
How does the amygdala contribute to depression?
Important in processing fear in humans
What is the link between BDNF and depression?
Studies have shown that decreased levels of BDNF can lead to depression
What is the role of the hippocampus in the brain?
Involved in memory, learning and responses to stress
What is known as the stress hormone?
Cortisol
- Released from the hippocampus
- Causes a decrease in BDNF
- High blood cortisol linked to depression
Explain the link between depression and eating?
Peripheral hormones such as leptin also exert centrally in the hypothalamus
Leptin plays a role in the bodies control of eating
What is postnatal depression?
Usually occurs 2-8 weeks after delivery and in some cases lasts for a year after birth of the baby
What is the effect of postnatal depression on the child?
Babies brain waves can become altered if the mother is depressed
What happens to a depressed patient if the reason for their depression goes?
Still stay depressed due to the biochemical changes at synapses
What is the forced swim test?
An animlal model for depression
- Put rodent in water - tries to escape and then despairs because can’t
- Second time put in the tank, rodent gives up trying to escape
- When given antidepressants - still tries to escape
How was suspending rats bother tails used to test antidepressants?
The rat keeps trying to turn the right way round until it despairs and just hangs
Second time despairs straight away
After given antidepressants keeps trying
How were trapped mice used to study depression?
Immobilised
Cortisol levels increase
Can see brain change sin amine neurotransmitters
What is the monoamine hypothesis?
That n depression is caused by a defect in noradrenaline and serotonin
Most dugs that affect these neurotransmitters don’t effect the patients for 6 weeks even though it causes an immediate decrease in the transmitters
- Suggests that they have long term trophic effects and could also effect synapse formation
How does cortisol contribute to depression?
Stress causes the release of cortisol which increases gene expression leading to neuronal apoptosis
How does activation of glutamate receptors lead to depression?
Can cause activation of genes that cause neuronal apoptosis
How do low concentration of monoamine transmitters and BDNF lead to depression?
They usually promote transcription of genes that cause neurogenesis - beneficial
If this is lost then there is less neurogenesis
What is the use of ketamine in depression?
Low concentrations of ketamine can work as an antidepressant
How does reserpine cause depression and Parkinson’s disease?
Depletes stores of monoamine transmitters
What are the three monoamines transmitters that act in the central nervous system?
Serotonin, Noradrenaline and dopamine
How does iproniazid work as an antidepressant?
First specific antidepressant
Inhibitor of MAO which is an enzyme involved in the break down of monoamines
How do selective serotonin reuptake inhibitors (SSRIs) work as an antidepressant?
Eg. Prozac
Stop the reuptake of serotonin to increase its action - low side effects - effective in patients whose primary biochemical problem is the 5HT pathway
How do classical tricyclic antidepressants (TCAs) work as an antidepressant?
eg. Imipramine
Work at the level of reuptake but are less selective then SSRIs as they uptake both serotonin and noradrenaline
How do monoamine oxidase inhibitors (MAOIs) work as an antidepressant?
MAO A enzymes are involved of the breakdown of monoamine transmitters in the central nervous system so by inhibiting them there will be more monoamines in the blood
What are the side effects associated with monoamine oxidase inhibitors as a treatment for antidepressants?
Monoamine oxidase type B act in the peripheral nervous system so if inhibit them can lead to unwanted side effects
eg. problems digesting amine rich foods such as cheese
- build up of tyramine in blood which is a precursor for dopamine goes into periphery and causes red flashed skin and fast beating heart
How do monoamine receptor antagonists work as a treatment for depression?
Presynaptic
- Release auto inhibition to increase post synaptic activity
What is the definition of pain ?
Paim is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
What is the difference between nociception and pain?
Nociception is the detection of an innocuous stimulus up to the spinal cord but pain is decided at the brain
What is the difference between primary and secondary neurones in detecting pain?
The primary order neurones are the first neurones to respond to the stimulus and the second order neurones are the go directly into the spinal cord
what part of the nervous system is responsible for the detection of pain?
Peripheral nervous system
What is the role of the CNS in pain?
Can change the perception of pain
Why is a spinal cord reflex not as a result of pain?
Because it just removes the limb from a potential innocuous stimulus and only goes to the spinal cord not the brain
What diseases cause extreme pain?
Primary erythermalgia - Red hands and feet constant inflammation Paroxydmal extreme pain disorder - Pain when they chew - Pain when pass stools
What disease causes no pain?
CIP (complete insensitivity to pain)
- Recessive condition
- Can hurt themselves andd not know
- Premature death
What is the difference between acute and chronic pain?
Acute
- Alerts the body to chemical, thermal and mechanical stimuli that has potential to damage body tissue
- Has a protective role
Chronic
- Accompanies chronic inflammatory diseases eg. arthritis
- Neuropathic pain results from damage to nerves eg. trauma, diabetes, cancer treatment
How much is spent on pain treatment across Europe annually?
$300 billion
What is analgesia?
The absence of pain without loosing consciousness
Where do analgesics target?
The pain circuit
- Dorsal root ganglia
- Spinal horn neurones
- Pain processing areas of the brain
What are the current analgesics available?
Non steroidal anti-inflammatory drugs (NSAIDS)
Paracetamol
Opioids
What are the problems with prolonged use of NSAIDS?
Cardiovascular risk
- NSAIDs can cause an increased risk of serious cardiovascular thrombotic events, myocardial infarction and stroke which can be fatal
Gastrointensinal risk
- Bleeding, ulceration and perforation of the stomach or intestines which can be fatal
What are the problems with the use of opioids as a painkiller?
Sedation - Apathy - Cognitive impairment Depression of respiration - Main cause of death - Combination with alcohol Inhibition of gastrointestinal trat Continuous use of opioids results in addiction
What are the classes of opioids and give examples of each?
Natural opioids: Morphine
Semi-synthetic opioids: Heroin
Fully synthetic opioids: fentanyl
Endogenous opioid peptides: endorphins
What are natural opioids?
Opium is the dried juice of the seed head of the poppy flower
Active ingredient morphine was isolated in 1806
How does morphine work?
Binds to opioid receptors: G protein coupled receptors which lead to inhibit calcium influx and stop release of glutamate
What are the three types of opioid receptors?
Mu, Kappa and delta
Why does morphine lead to side effects?
Because there are opioid receptors found everywhere in the body
What is dermorphin?
Another natural opioid isolated from the skin of leaf frog
- 30-40 times more potent than morphine on Mu receptors
- stable due to a non natural amino acid so is longer lasting
How does heroin differ to morphine?
Derived from morphine in 1874
Acetate groups added which make it more hydrophobic and hence penetrated the brain barrier easier
What is fentanyl?
A synthetic opioid
- 100 times more potent than morphine
- fast-acting opioid
- Used during surgery
What is an endogenous opioid?
Naturally occurring peptide that are found mainly in the CNS
- Release during stress and prolonged physical exercise
What was the first endogenous opioid discovered?
Enkephalin
What do mutations in Nav1.7 lead to?
Loss of function
- Lead to absence of pain
Gain of function
- Lead to pathological pain - increased
How are monoclonal antibodies used as a new approach to analgesics?
Against never growth factor help in some chronic pain conditions
Very expensive
How is botox used as a new approach to analgesics?
- Block neurotransmitter release
- Botox is internalised in presynaptic neurone
- Releases enzyme that breaks down snare proteins that are required for neurotransmitter release
What are the functions of the noradrenergic pathways in the CNS?
Pain, arousal, mood, blood pressure regulation
Regulating sensory processing relates it to withdrawal increased sleep. anorexia
How is Noradrenaline synthesised?
Tyrosine amino acid is converted to DOPA which is precursor of dopamine
Dopamine is converted to noradrenaline in neurones where dopamine B-hydroxylase enzyme is found
How does noradrenaline regulated serotonin release?
Neurones that release serotonin have NA receptor
When these receptors are activated more serotonin is released
- It is suggested that depressed people have less receptors
How do a2 adrenoreceptors regulated serotonin?
Found presynaptically and have inhibitory serotonin release through a feedback mechanism
- Increase noradrenergic transmission will lead to desensitisation as they will be chronically activated and internalised
- Removing feedback inhibition increases serotonin as less receptors
What are the functions of the serotonergic pathway in the CNS?
Hallucinations, sleep, wakefulness, mood and emotion, feeding behaviour
What are drugs acting serotonin transmission used to treat?
Depression, anxiety, migraine, anti-psychotic
What is anhedonia and what causes it?
The inability to gain pleasure from normally pleasurable experiences
- the role of serotonin in regulating the limbic processing relates
What amino acid is used in synthesis of serotonin?
Tryptophan
- An essential amino acid that needs to be consumed
- This is converted into 5HT
How is the release of serotonin mediated?
Through G protein coupled receptors - potential therapeutic target
How is serotonin terminated?
Terminated through uptake mechanisms (target for SSRI drugs) and broken down by enzymes MAO (target for drugs) and COMT
Why is there a delay in the action of SSRIs?
Drugs like prozac- symptoms gets slightly worse before better
5HT1 receptors found in dendritic regions and on GABAnergic interneurones in the cortex promote inhibition of serotonin release causing increase in symptoms
The receptors then becomes desensitised and internalised and therefore increases serotonin
What is the relationship between BDNF and depression?
People with depression have decreased levels of BDNF in hippocampus
How does serotonin regulate levels of BDNF?
Activation of serotonin receptors, increases cAMP (coupled to Gs), to activate protein kinase A, increases activity of transcription factor CREB ethic increases levels of BDNF
How do SSRIs increase the levels of BDNF?
Serotonin activates receptors couples with Gs which activated transcription factor of BDNF but inhibits receptors coupled with inhibitory proteins which would inhibit the transcription factor
How does a decrease in BDNF lead to depression?
Because BDNF is responsible for stabilising synaptic connections and promoting synaptogensis in hippocampus so without it this doesn’t happen - depression
How is bipolar disorder treated?
Lithium - Permeates voltage gated ion channels, inhibits inositol monophosphatase and glycogen synthase kinase 3 signalling Antiepileptic drugs - Mood stabilisers - eg. valproate
What is the prevalence of schizophrenia?
1.1% of people over the age of 18
What are the symptoms of schizophrenia?
Negative
- Blunting emotions, withdrawal from society, anhedonia, reluctance to perform everyday tasks
- Increase with age
Positives
- Frightening and consist of hallucinations, delusion, thought disorders and aggression
- May be accompanied by anxiety an depression
What are the causes of schizophrenia?
Hereditary and is a result of abnormalities which arise early in life and disrupt normal development
- No single gene
Als environmental
- eg. overuse of cannabis
How does a schizophrenic brain differ to a normal one?
Larger lateral ventricles
Small volume of tissue in left temporal lobe
What is the effect of drugs that enhance dopamine signalling?
Increase positive schizophrenic like symptoms
What are the dopaminergic pathways in the CNS?
Nigrostatial pathway - fine motor control
- loss of this causes Parkinson’s
Mesocortical and mesolimbic system
- Effects behaviour, compulsion and reward pathways
- Schizophrenic
Tuberohypophyseal pathway
- Pituitary hormone secretion eg. prolactin
Medullary chemoreceptor trigger zone
- Nausea and vomiting
-Side effects to drugs treating schizophrenia
How is dopamine synthesised?
By precursor of DOPA
How is dopamine terminated?
With uptake mechanisms and broken down by COMT and MAO
What is the effect of amphetamines and cocaine on dopamine and noradrenaline?
Amphetamines stimulate secretion of DA and NA, inhibit MAO and metabolism of DA and NA, displace DA and NA from vesicles, cause re-uptake transporters to work in reverse
- Increases motor activity that produces positive symptoms associated with schizophrenia
- Effects of appetite
What are the treatment of schizophrenia?
D2 antagonists
- 80% occupancy to decrease postive symptoms
Phenothiazines - antipsychotics
- Long term use leads to tardive dyskinesia
Atypical antipsychotic drugs
- Reduced side effects
What is the sliding myofilament hypothesis?
The neuronal action potential causes a muscle action potential which increases intracellular Ca2+
Ca2+ cause cross bridges between actin and myosin to form
Myofilaments slide causing contraction
More overlap between mysoin and actin before cross bridges form, the more tension
What is the motor unit?
Th motor neurone and the muscle fibres it innervates
What does more motor units say about contraction?
More graded contraction -spatial summation
What is the role of Nav channels in the pre and post synaptic neurone in a neuromuscular junction?
Mediate depolarisation
What is the role of Kv channels in the ore and post synaptic membranes of a neuromuscular junction?
Mediate repolarisation
What is the role of Cav in pr synaptic membrane of a neuromuscular junction?
Mediates influx of Ca2+ causing fusion of vesicles containing ACh to fuse with the membrane and be released
What is the role of AChR on the post synaptic membrane of the neuromuscular junction?
When activated by ACh causes the release of Ca2+ starting muscle contraction
What does a skeletal muscle action potential look like?
Same as neuronal action potential
What is conductance?
The measure of the number of ions crossing the membrane
What are the two types of AChR receptors?
Nicotinic and muscarinic
- Nicotinic are ligand gated
- Muscarinic are GPCR
What is a nicotinic AChR?
A non selective ligand gated cation channel - permeable to Na and K so Nernst potential is 0mv
Causes depolarisation when open
What is the structure of the nicotinic AChR?
Has 4 types of subunits: 2alpha:beta:gamma:delta 2 binding sites - Both must be activated in order for the channel to be open 4 transmembrane domains
How many versions of the gene coding for nicotinic AChR are there?
9
Gene = CHRNA
CHRNA1 is found in skeletal muscle and the rest are found in neuronal tissue
What is the gating process for the nicotinic AChR?
When no agonist bound - closed (C)
When one agonist bound -closed (A1C)
When two agonists bound - momentarily closed (A2C)
When two agonists bound - Open (A2O)
How many molecules of ACh are there in the neuromuscular junction?
200 vesicles
- so 6000 to 10000 molecules
What is myasthenia gravis?
An autoimmune disease that generates antibodies that target neuromuscular junctions
Affects 2-7 per 10000 in UK making it the most common neuromuscular junction disorder
What are the symptoms of myasthenia gravis?
Weakness and tiredness in skeletal muscle
Can be fatal due to respiratory failure
How does myasthenia gravis cause its symptoms?
The antibodies bind to the AChR on postsynaptic skeletal muscle meaning that ACh can’t bind
Receptors that have an antibody bound to them become internalised - reduces amount of receptors
What is the age of onset of myasthenia gravis?
Women - 30’s
Males- 60-70’s
How do we know that myasthenia gravis is an autoimmune disease?
Individuals who don’t have myasthenia gravis have much less antibodies against AChR as shown in an antibody experiment
Individuals with varying severity of myasthenia gravis have a much higher amount of these antibodies
What happens if you inject mice with the antibody against AChR?
It will display mild symptoms of myasthenia gravis
Causes fewer action potentials fired and smaller compared to a control
What are the treatments for myasthenia gravis?
Acetylcholinesterase inhibitors - For mild cases - Stops break down of Ach increasing it - e.g.. pyridpstigmine Corticosteroids and other immunosuppressant - From moderate to severe - reduces antibody levels - e.g. predinisolone, cyclosporin Iv immunoglobulins - Severe - Inject immunoglobulins so that the antibodies bind to them instead Plasmapheresis - For acute - Removal of the antibodies from the plasma like dialysis Thymectomy - Tumour removal - Mechanism not clear
Give evidence for the use of acetylcholinesterase inhibitors as an effective treatment of myasthenia gravis?
Mouse with mild myosthenia gravis improve to normal with the addition of these inhibitors
What are transverse tubules and what do they do?
Invaginations of the muscle fibre
Meaning the action potential drops down into transverse tubule allowing sufficient Ca2+ to be released for contraction
What are the two ways that Ca2+ can cause skeletal muscle contraction?
From outside the cell
- Action potential causes L-type Ca2+ channels to open and Ca2+ enters cytosol of cell
From the sarcoplasmic reticulum
- Ca2+ enters the cytosol through ryanodine receptors which are activated by coupling with L type calcium channel
How are ryanodine receptors activated in cardiac muscle?
Calcium induced calcium release
- The open probability changes due to Ca2+ entering through L-type calcium channels
What calcium transport proteins are involved in moving Ca2+ from extracellular to intracellular?
Ca2+ ATPase
Na+/Ca2+ exchanger
What calcium transport proteins are involved in moving Ca2+ from intracellular to extracellular>
Ca2+ ATPase
Calrectulin - bind calcium and store it
What is myotonia?
Hyper excitability of skeletal muscle which affects the frequency and length of action potential
Causes muscle stiffness and delays relaxation
And myotonic seizures
What is the incidence of myotonia?
1:23000 to 1:50000
What are the two types of myotonia?
Myotonia congenita
Paramyotonia
What is myotonia congenital?
A type of myotonia caused by a loss of function mutation in CLC1 channel
What are the two types of myotonia congenita?
Thomsen’s autosomal dominant
Beckers autosomal recessive - more severe, earlier onset
What are the ‘fainting goats’?
Mutations in CLC1 channel like humans
Animal model for myotonia congenita
When seizure hits- falls over
What are models for myotonia congenita?
Fainting goats
Myotonic mice
- Mutations in CLCL
What is the role of the CLC1 channel?
Cl- channel that helps set the resting potential working with K+ channels
- Nernst for Cl- is -70mv so when these channels open the membrane potential is drove towards it
In a normal person, how many of the CLC1 channels are open at resting membrane potential?
About half
What happens in the mutation that occurs in the CLC1 that changed glycine to arginine ?
Causes myotonia congenita
- Requires a more positive potential for the same amount of channels to be open compared to wild type
- Cl- channels can’t contribute to resting potential so it is less negative then it should be
In someone with myotonia congenita, do they require more or less action potentials to cause contraction?
Less
- Resting membrane potential is closer to the threshold
- Increases contraction
What is the treatment for myotonia congenita?
Mexilitene
- Inhibits Na+ Channels
- Must use lower possible dose otherwise it would block all skeletal muscle
What is paramyotonia?
A type of myotonia
- Caused by a fain of function mutation in Nav1.5
- Causes issue with inactivation gate meaning channels do not close so more Na+ enters the muscle and depolarisation is prolonged
What is the effect of the cold on paramyotonia?
Cold enhances the trigger
- In a normal individual - cold causes a small increase in [Na+]
- In a Nav1.4 mutant - a massive increase in intracellular [Na+] in cold - much more sensitive
What is malignant hyperthermia?
A inherited autosomal dominant disease that is asymptomatic until patient is under the general anaesthetic halothane
What is the incidence of malignant hyperthermia?
1 in 10,000-50,000
What is the chance of survival of an individual with malignant hyperthermia after an attack?
80% death rate
If treated 10% death rate
What are the symptoms of malignant hypothermia?
- Rise in body temperature by 1 degree every 5 mins - proteins will denature after 25 mins
- Tachypnea (rapid breathing)
- Low plasma O2
- High plasma CO2
- Tachycardia
- Rigidity (high contraction of muscle)
- Sweating
- Shifts blood pressure
What happens if malignant hyperthermia isn’t treated?
Would die of respiratory and lactic acidosis
- The muscular rigidity causes muscle breakdown releasing K+ causing hyperkalemia - effecting cardiac and neuronal excitability - death
Why does malignant hyperthermia cause a huge rise in boy temperature?
Because excessive muscle contraction will lead to excessive ATP hydrolysis (releasing heat)
Because the ATP is being used up more must be made - also producing lots of heat
What mutation causes malignant hyperthermia?
Many different gain of function mutations found on the N terminus of the ryanodine receptors found on the sarcoplasmic reticulum of skeletal muscle
Give an example of how humans have a had a big impact on the incidence of diseases in animals?
Pigs
- Mutation at position 614 on the N terminus of the ryanodine receptors causes malignant hyperthermia in both pigs and humans
- In pigs it is called porcine stress syndrome as it is activated by both anaesthetics and stress
- Causes pigs to have a bigger muscle mass so desirable to farmers
- Incidence became higher
What does the mutation at position 614 on RyR1 receptors in a rabbit lead to and explain the experiment showing this?
Model for malignant hyperthermia
Affects with halothane
- Wild type no change
- Mutant -increase in intracellular [Ca2+]
Affect with caffeine
- Wild type - ryanodine receptors can be activated with very high levels (15mm)
- Murant - responds at a much lower level of caffeine
What is the treatment for malignant hyperthermia?
Dantrolene - inhibits RyR1
IV hydration
Diuretics - stops kidney damage from muscle breakdown products
NaHCO3 - Counter acidosis
Mechanical hyperventilation to remove CO2
What is tetrodotoxin?
A guanidinium neurotoxin that is produced by marine bacteria and founds in animals such as pufferfish and the blue ring octopus
How lethal is tetrodotoxin?
10-100 times more than black widow spider venom
10000 times more lethal than cyanide
What are the symptoms of tetrodotoxin after it has been ingested?
Numbness lips and tongue Facial paraesthesia (tingling) Headache Nausea Dizziness Diarrhoea Vomiting Increasing paralysis Respiratory paralysis leading to death - 20 mins to 8 hours
What are the symptoms of tetrodotoxin after bitten?
Pretty much the same as ingested but without facial effects
- Faster time to death
What is the treatment for tetrodotoxin?
Mechanical ventilation (because you die from not breathing) No anti venom as it binds too strongly to site of action
What is the site of action for tetrodotoxin?
Inhibits voltage gated Na+ channels on both pre and post synaptic membrane
- Inhibits depolarisation and loses the ability to contract
- Causes failure of neurotransmission and reduction of neurotransmitter release
Why does loss of sensation occur before paralysis in tetrodotoxin poisoning?
Because sensory nerves are on the outside of bundles so the toxin reaches them first
Which voltage gated Na channels are tetrodotoxin sensitive and insensitive?
Nav1.1-1.7 are sensitive (not 1.5)
Nav1.5, 1.8 and 1.9 are insensitive
What determines whether voltage gated Na+ channels are sensitive to tetrodotoxin?
Determined by specific amino acids
In rats
- Wild type as concentration of tetrodotoxin increases inwards current decreases
- E387Q mutants ( which changes glutamate to glutamine in the pore region of the channel) - sensitivity to TTX decreases
Which amino acid is responsible for TTX sensitivity?
Tyrosine
- Brain and muscle Nav at position 374 - tyrosine and is TTX sensitive
- Heart Nav at 374 - cysteine - TTX insensitive
- if you change heart Nav cysteine to tyrosine then it becomes sensitive
Give an example of how sensitivity to TTX shows natural selection?
In garter snakes
- Two types - bear lake snakes and willow creek snakes
- Same species but different geographical locations
- Bear lake are sensitive and willow creek aren’t
- Willow creeks can eat salamanders which have TTX meaning they are more likely to survive than those who are sensitive
What are dendrotoxins?
A snake neurotoxin part of the mamba family
They inhibit Kv channels so inhibit repolarisation
What are the symptoms associated with dendrotoxins?
Early - Weakness/numbness in the bitten extremity Systemic resposes - 30 mins to an hour - Ptosis (drooping eyelids) - Ophthalmoplegia (paralysis of eye muscles) - Dysphagia - Paresis - Respiratory failure - death
What is the site of action of dendrotoxins?
Kv channels
- If blocked in sensory and motor neurones then it blocks repolarisation meaning access neurotransmitters initially released and then no more stores available so no more released - paralysis
What is conotoxin?
A group of toxins released from a cone snail
- Has multiple targets and varying degrees of lethality
What are the targets for conotoxins?
Affects nociceptor and spinal cord
Blocks Nav in nociceptors which stops pain
What are the symptoms associated with conotoxins?
Varying depending on the species and toxin
- Burning pain
- Swelling
- Numbness
- Muscle weakness
- blurred vision
- Paralysis
- Coma
- If lips become stiff - associated with death
