ICPP Flashcards
(153 cards)
1
Q
Describe main features of fluid mosaic model of the cell membrane
A
Amphipathic
Fluid - lipids are in motion within the bilayer
Affected by temp and molecular mass.
Mosaic - many membrane proteins embedded in bilayer
Lipid motions:
Intra chain
Fast axial rotation
Lateral diffusion
2
Q
Recognise the main membrane lipids - 4
Recognise their head and tail
A
2 types of phospholipids:
1) Glycerophospholipids (normal). Can have different heads attached to phosphate group that are polar and charged.
2) Sphingomyelin - is a sphingosine combine with a fatty acid chain joined to a phosphate group. Can also have choline or ethanolamine attached.
Glycolipids - are sphingomyelin without the phosphate group. Have sugar group attached(head). Can be cerebrosides (monosaccharide) or gangliosides (oligosaccharide with Sialic acid residues).
Cholesterol - hydrophobic tail (steroid rings) and hydrophilic head (OH group).
3
Q
Main lipid membrane properties
A
Glycerophospholipids- acyl chains can be saturated or not. Can have diff lengths. Thermodynamically most stable arrangement.
Sphingomyelin- mostly saturated acyl chain and unsaturated are trans so no kink so close packing.
Glycolipids - sugar groups extends extend reach of membrane so used for cell recognition and important in immune system for this.
Cholesterol - polar head binds to carbonyl group on fatty acid chain which limits movement and rigid steroid rings interfere with crystalline structure so reduce mobility and inc stability.
4
Q
how do amphipathic molecules behave in aqueous
environments and how does this leads to the formation of lipid bilayers
A
The amphipathic molecules form one of two structures in water, micelles and bilayers.
The bilayer formation is spontaneous in water and is thermodynamically driven. Tail and head optimally energetically stable.
Extensive non- polar attractive forces between the hydrophobic tails and electrostatic and hydrogen bonding of head with water.
5
Q
Discuss the influence of unsaturated fatty acids and
cholesterol on membrane fluidity
A
Adding unsaturated phospholipid goes from gel to more fluid as it cannot closely pack. Downwards shift of temp at which membrane is fluid.
Cholesterol allows fluid nature to be maintained over a wider temp range. Buffer.
At higher temp - Polar head interacts with acyl group of PL head – limits movement.
At lower temp - interferes with crystalline packing.
6
Q
Understand how sphingolipids and cholesterol regions of
the membrane form rafts
A
Congregation of sphingolipids and cholesterol, which have reduced mobility compared to rest of membrane, allows selective hosting of specific proteins.
Inc tight packing. Can have GLs.
Reduced mobility of raft optimises signalling stability and limits random drift of proteins.
Act as organising domains for
receptors and signalling molecules
Optimise kinetic interaction for
signal transduction
7
Q
Recognise the key role of hydration in maintenance of
physiological membrane structure and function
A
Allows it to form bilayer as it interacts with head.
Variation by 10% affects function.
Water interacts with polar regions stabilises the lipid head regions.
8
Q
Understand the importance of flexibility and elasticity in the
cell membrane
A
Cell membranes need to be able to transmit forces:
Throughout own cell structures In synchrony with other cells tissues–organs – body
The elasticity of the bilayer is essential when forces act upon the membrane and distort its shape. When the force is removed it can then ‘bounce’ back into shape.
9
Q
Appreciate Major Functions of the Cell Membrane
A
Continuous, highly selective permeability barrier
Control of the enclosed electrochemical environment
Communication
1 - Recognition 2 - Signalling
3 - Adhesion proteins 4- Immune Surveillance
Signal generation in response to stimuli (electrical, chemical)
10
Q
Recognise proteins are flexible and elastic – a key
structural feature that enables function
A
Proteins direct forces throughout its chains and active sites to change structure to perform specific roles.
Peptide chains can flex through single bond structure.
Can store and release energy when acted upon by a force.
Changes in conformation require specific biological signal.
11
Q
Phoshatidyl
A
Choline most common
Inositol - key signalling role
12
Q
Know that hydration is essential to both protein structure and function
A
Need to incorporate water as an essential part of their biological structure.
Can enter hydrophilic crevices within protein if accessible
Water stays away from hydrophobic regions - this still
contributes to shaping of the functioning protein.
13
Q
Recognise proteins exhibit varying degrees of mobility
within the membrane bilayer
Look at notion
A
Lateral diffusion
Rotational - F 1 /F0 ATPase
Conformational change
14
Q
Understand conformational changes in proteins
underpin protein function
A
They are adopted following interactions with specific molecular or bioelectric signals.
These conformational states contribute to conveying further signals within the cell for example via G-proteins. They can also contribute to directed molecular movements as part of a larger task eg actin/myosin mediated contraction.
15
Q
Recognise the different categories of the relationship of
proteins with the membrane
Look at notion
A
2 major groups - peripheral and integral
Peripheral proteins- external and internal membrane face
Integral:
Allow molecules to interact eg receptor kinases, transporters etc.
Not removed by ionic change.
non-polar bonding occurs within the hydrophobic interior of the lipid bilayer. Peptide chains on external and internal membrane face have
mainly polar residuals to interact with polar head, water, ions, peripheral proteins etc.
internal:
provides flexibility and elasticity of whole cell membrane
enzymes and important regulatory subunits of receptors, ion channels and transporters.
Disperses forces throughout network to protect cell integrity from mechanical disruption
External:
Essential for transmission of mechanical force generated
enzymes, antigens and adhesive molecules that attach the extracellular matrix.
Lipid Anchored Proteins
covalent link via fatty acid/lipid group within bilayer
Functional protein is outside membrane – can move laterally eg G proteins
16
Q
Describe restrictions on protein movement in the
membrane - exemplified by integral and peripheral
protein cell - cell interaction
A
Aggregation - lipid rafts
Tethering - Extracellular and Intracellular - integrin
Cell – Cell Interaction - cadherins
17
Q
Describe cytoskeletal elements in RBCs - 3 groups, 7 proteins
Look at notion
A
1.Transmembrane proteins
2. Intermediate Anchoring Proteins connecting 1 & 3
3. Long flexible/elastic force carrying proteins
1 -2 -3 interact via electrostatic non-covalent bonds
Trans - band 3.1 and glycophorin
Band 3.1 - essential transporter in carriage of CO2
Glycophorin - antigen – reduces adhesive/friction forces
Also shape biconcave and enable forces to be distributed through whole structure.
Intermediate- Ankyrin
Anchors Band 3.1 to Spectrin
Adducin – Actin – Band 4.1
Band 4.1 anchors Glycophorin Adducin Stabilises Assembly
Interact via polar bonds
Flexible - spectrin - double helix - Transmits forces throughout whole RBC
18
Q
Describe how cytoskeleton imparts great structural
flexibility exemplified by RBCs
A
RBC has immense flexibility and elasticity • (ie stores Potential Energy - Releases Kinetic energy) due to weak but large number of electrostatic forces.
• Cortical cytoskeleton extends lifespan ≈ 120 days.
19
Q
Example loss of cytoskeletal integrity in Disease and
Drug Therapy
A
Cytoskeleletal protein mutations - loss of RBC structural integrity
Hereditary Spherocytosis - rigid, Forces cause pinched off microvesicles - loss of O2
carrying capacity
Cytochalasin in chemotherapy Inhibits polymerisation of actin filaments in cancer cells so incorrect anchoring of spectrin with glycophorin in RBCs
20
Q
Cortical cytoskeleton
A
Cell cortex - layer of actin beneath membrane
21
Q
Ses 2
A
22
Q
What is the membrane to permeable to? How is it measured.
Look at notion for coefficient diagram
A
extremely permeable to small uncharged gas molecules such as O2, CO2 and N2.
Then Small Uncharged Polar Molecules - This includes water, urea and NH3.
Large Polar Molecules - This includes sugars and amino acids.
Inorganic/Organic Ions
Permeability coefficient scale is cm/sec
23
Q
Describe the general factors in Fick’s Law determining the rate of passive diffusion for lipid soluble solutes. No need to know equation.
A
J = P (C1-C2)
Diffusion coefficient = factors affecting permeability x diff in concs
24
Q
What are impermeable solutes selectively transported via?
A
membrane proteins classed as: Pores; Channels; Carriers
25
Describe Pores Channels and Carriers
Look at notion for diagram of mechanism and differences between them.
Pores - AQPs are always open so controlled add or removal from membrane by hormones.
+ charged residues in the pore prevent the movement of H+.
Selectivity means ion gradients are not disrupted.
Integral membrane proteins and bi- directional.
Channels - 1 gate, need specific signal to open, allow ions through, depends on electrochemical gradient. Ping pong transport.
They consist of a number of transmembrane subunits.
Main types are ligand gated ion channels(receptor proteins) or VG.
Both facilitated diffusion.
Carrier/transporters - Like enzymes get saturated. 2 gates. Facilitated or active transport. Sequential binding and conformational changes.
Uniporter(1 substance in 1 direction), symporter(2 or more in same direction) or antiporters(2 or more in opp).
All have hydrophilic centres and central aqueous core.
26
Understand the basic principles of: Passive and Facilitated Diffusion, and Active Transport
Passive - ficks law, conc gradient is energy source
Facilitated- same but needs to travel through protein
Active transport- ATP is energy source. Against gradient.
27
Distinguish between Primary and Secondary Active Transport
Primary - Whenever ATP is used directly to transport a solute AGAINST ITS ELECTROCHEMICAL GRADIENT
Secondary- Whenever an electrochemical gradient set up by an ATPase - such as that for Na+ - is then used to transport another ion or solute AGAINST its Gradient
28
Compare the primary active transport mechanisms of the main ATPases and their roles in regulating ion flow. Look at ATP synthase videos.
3 main types- P, F and V
P-type = pump:
Na+/K+ ATPase
need ATP hydrolysis (ATP phosphorylates aspartate) and has sequential changes in conformation and affinity.
3 Na+ in and 2 K+ out. Electrogenic antiporter.
Ca2+ ATPase are PMCAs.
ATP hydrolysis to release Ca2+ and H+ out.
Needs Mg2+ as co-factor.
In sarcoplasmic reticulum - SERCAs - Ca2+ in, H+ out.
K+/H+ ATPase in parietal cells in stomach. K+ in and H+ out.
F1/F0 ATPase - ATP synthase
29
Describe the Symporters and Antiporters that serve as Secondary Active Transporters using electrochemical gradients as the energy source - look at notion
Both electro-neutral
Symporters:
SGLTs - there is 1-5, use 1Na+ for 1 glucose(SGLT 2) or 2Na+(SGLT1).
Antiporters:
NCX
NHE - Exchanges extracellular Na+ for intracellular H+
• Electroneutral
• Regulates pHin
• Regulates cell volume
• Activated by growth factors
• Inhibited by amiloride (a potassium sparing diuretic)
30
Describe how ions and sugars are transported across membranes using:
Facilitated diffusion
Active transport
31
What is a semi-permeable membrane?
A layer through which only allowed substances can pass
32
Physiological roles of transporters
Maintenance of ionic composition
• Maintenance of intracellular pH
• Regulation of cell volume
• Concentration of metabolic fuels and building blocks
• The expulsion of metabolic waste products and toxic substances
• The generation of ion gradients necessary for the electrical excitability
of nerve and muscle (excitable tissues)
33
Sodium pump functions
Drives Secondary Active transport
Control of pHi i
– Regulation of cell volume and [Ca2+]i H+ or Ca2+
– Absorption of Na+ in epithelia – Nutrient uptake, e.g. glucose or
glucose, amino acids from the small intestine
• K+ diffusion through ‘leaky’ channels is mainly responsible for resting
membrane potential (-70 to -90 mV)
34
Ses 3
35
Recall the pH scale
normal pH in tissues, plasma and cytoplasm
Is there variation- notion
0.3 inc halves H+
– log10 [H+]
Human tissue survival is pH 6.8 - 7.8. Plasma pH is 7.35-7.45.
Cytoplasmic pH is 7.2, but varies widely across other organelles
36
Why is pH control important - 1 general and 2 clinical
pH changes can cause a change in net electrical charge on proteins and other biological molecules. This disrupts electrostatic interactions and hydrogen bonding so alters protein structure and function. Alters binding of substrates and
ligands.
R-COOH —> R-COO- + H+
R-NH3+ —> R-NH2 + H+ •
Clinical:
Tissue ischaemia – e.g. cardiac ischaemia and stroke
• Reduction in blood flow decreases O2 supply
• Switch to anaerobic glycolysis leads to cytoplasmic acidification • Over-activation of Na-H exchanger 1 leads to
intracellular Na overload and consequently Ca overload via Na-Ca exchanger
• Altered cellular function eg arrhythmias, apoptosis or necrosis
Dents disease
characterised by proximal tubule
dysfunction and progressive renal failure.
• Due to mutations in CLC5 (which is 2Cl-/H+ exchanger)
and defects in endocytosis – due in part to impaired acidification.
37
Why is cell cytoplasm acidic, how is pH buffered - notion
And why is this not enough
1. The electrochemical gradient favours inward movement of H+ and outward movement of HCO3-.
This creates an transmembrane pH gradient and an electrical gradient.
2. Also during metabolism CO2
production causes proton
generation:
CO2 + H2O —> H2CO3 —> H+ + HCO3-
3. In anaerobic glycolysis glucose is metabolised to lactic acid
Buffers only reduce the impact of acute changes to intracellular pH and are insufficient on their own. Regulated transport processes are required to prevent H+ accumulation and acidosis.
38
Describe how cytoplasmic pH is primarily regulated by
the ensemble activity of Na+/H+ exchanger and the Cl-/HCO3- exchanger - notion for graph
NHE - most cells - alkalises
• Exchanges extracellular Na+
for intracellular H+
• Electroneutral 1:1
• Regulates pH in H+
• Regulates cell volume
• Activated by growth factors
• Inhibited by amiloride
Acidification activates activates NHE and NBC.
AE - most cells - band 3 - acidifies
Cl- in and HCO3- out
Activated by alkalisation.
pH is held at the set point. Any drift away from this pH is corrected by the increased activity of either the Na+/H+ or Cl-/HCO3- exchangers.
39
Why is cell vol regulation important
Excessive swelling jeopardizes membrane integrity.
Swelling or shrinking can interfere with cell cytoskeleton.
Cellular functions depend on correct hydration of proteins.
H2O is able to passively diffuse across plasma membranes – so intracellular volume is sensitive to extracellular osmolarity
40
Outline the response of cells to moderate osmotic stress
and describe mechanisms of regulating cell volume - notion for particular transporters
• No standard method for cell volume regulation
• Different cell types use particular combinations of transporters to achieve the regulation they need
• Transport of osmotically ‘active’ ions, • e.g. Na+, K+, Cl- or organic osmolytes
(amino acids) • Water follows • Net extrusion of solutes – cell shrinkage
• Net influx solutes – cell swelling
41
Describe how organic anion transporters (OATs) and
organic cation transporters (OCTs) mediate the cellular
uptake of organic anions and cations.
SLCs are secondary active or facilitated transporters.
The SLC22 subfamily consists of
split into 2 main subfamilies OATs and OCTs.
OATs - Natural substrates eg vitamins, prostaglandins.
Common drugs - antibiotics, antivirals, diuretics, NSAIDs.
OCTs (eg dopamine, serotonin, histamine, choline) - 1-3, passive carriers - facilitated diffusion, uses electrochemical gradient.
Both commonly localised on epithelial and endothelials cells and regulate solute transport between fluid compartments.
42
Describe the role of OATs and OCTs in drug transport,
elimination and toxicity.
Many drugs are hydrophilic.
For drugs to reach their target, carriers are required at each membrane boundary from site of administration.
OAT/OCT expression profiles can influence drug side effects and toxicity. They are uptake transporters so used by drugs.
Eg OAT/OCT drug transport in the kidney shortens plasma half-life (e.g. penicillin).
Probenecid used to extend half life of penicillin by blocking OAT so less elimination.
43
Give specific examples of drug uptake and transport by
OATs and OCTs in the kidney.
44
Describe how OCTs and OATs may influence responses
to drugs.
Metformin – first line drug for treating type 2 diabetes
Key site is the liver -to
decrease hepatic glucose production.
Some patients express variant alleles for OCT1 that reduce OCT1 activity.
In these patients Hepatic uptake of metformin is reduced and blood glucose lowering effects are reduced.
45
Discuss the role of OCTs in cytotoxicity associated with
kidney damage, hearing loss and sensory neuropathy. Notion
Cisplatin is Important for treatment of various metastatic and inoperable tumours.
Toxicity is due to cisplatin being an excellent OCT2 substrate but a poor substrate of either MATE1 or MATE2-K
Cisplatin accumulates in proximal tubule cell to cause cell death - kidney damage.
Kills hair cells and accumulates in neurones - sensory neuropathy.
46
Ses 4
47
Outline what a membrane potential is
Membrane potential is the difference of electrical charge
that exists across the plasma membrane.
It is always expressed as the potential inside the cell relative to the extracellular solution.
48
Membrane potential of cells
Smooth muscle myocytes = -50mV
Neurones = -70 mV
Cardiac myocytes = -80 mV
Skeletal muscle myocytes = -90 mV
49
how the resting
membrane potential of a cell may be measured
Zero electrode outside cell
Then put microelectrode into cell
Membrane potential dips and voltmeter has negative reading
Therefore, membrane potential is more negative compared to outside cell.
50
explain how the selective permeability of cell membranes
arises
Enabled by the phospholipid bilayer (prevents passive diffusion of ions) and ion channel properties.
They are:
Selective for ion species
Gating - open or close due to conformational change
Ion flow - down electrochemical gradient
Ion selectivity of channels and the types of channel that are open makes the whole cell membrane selectively permeable to ions
51
Describe how the resting potential is set up given the
distribution of ions across cell membranes.
Resting membrane potential arises because it is selectively permeable to K+.
K+ ions diffuse down their chemical gradient until the chemical gradient is at equilibrium with the electrical gradient.
At this membrane potential there is no net movement of the ion (electrochemical gradient is zero), but a voltage has been generated.
52
Explain the term equilibrium potential for a given ion
Ions will diffuse down their chemical gradient until the chemical gradient is at equilibrium with the electrical gradient.
This is equilibrium potential for the ion.
53
Nernst equation notion
The Nernst equation allows you to calculate the membrane potential at which an ion will be in equilibrium, given the extracellular and intracellular ion concentrations.
54
How do membrane potentials change
Make membrane more permeable to other ions eg Na+ which changes it to +60mV
55
Describe how Na+/K+ ATPase maintains Ion Gradients set
up by the Cell
over time, leakage of ions in real cells will lead to a slow collapse of ion gradients. We therefore need to invest energy into maintaining the RMP, which is the job of the Na+/K+ ATPase pump.
56
Define depolarization, hyperpolarization and repolarisation, and explain
the mechanisms that may lead to each of these
Depolarization - A decrease in the size of the membrane potential from its normal value.
Opening Na+ or Ca2+ channels causes it.
Hyperpolarization - An increase in the size of the membrane potential from its normal value.
Caused by opening K+ channels.
Repolarisation - returning to RMP
57
outline some of the
roles of the membrane potential in signalling within and
between cells.
Nicotinic Acetylcholine Receptors 1. Have an intrinsic ion channel 2. Opened by binding of acetylcholine
3. Channel lets Na+/Ca2+ in and K+ out, but anions do not move
4. Moves the membrane potential towards 0 mV,
intermediate between ENa
and EK
58
Gated channels
1. Ligand Gating
• The channel opens or closes in response to binding of a
chemical ligand
2. Voltage Gating
Channel opens or closes in response to changes in membrane potential
3. Mechanical Gating
• Channel opens or closes in response to membrane
deformation
• E.g. Channels in mechanoreceptors: carotid sinus stretch receptors, hair cells
59
Chemical synapses - fast, (excitatory, inhibitory) and slow notion for slow explanation
Chemical synapses occur between: nerve cell – nerve cell
nerve cell – muscle cell
nerve cell – gland cell
sensory cell – nerve cell
Fast - receptor protein is also an ion channel. Receptors make synapses excitatory or inhibitory.
Excitatory- when transmitters bind to ligand-gated channels which cause membrane depolarization.
Can be permeable to Na+, Ca2+, sometimes cations in general (nAChR).
Resulting depolarization is called an Excitatory post-synaptic potential (EPSP).
Inhibitory - ligand gated channels cause hyperpolarisation.
Permeable to K+ or Cl-.
Inhibitory post-synaptic potential (IPSP).
Slow - receptor and channel are separate proteins.
Direct G-protein gating - localised and rapid. When transmitters binds to receptor parts of G protein break off and bind to channel to open.
Gating via an intracellular messenger
60
factors that can influence membrane potential
1. Changes in ion concentration
• Most important is extracellular K+ concentration (3.5-5.5 mM normal)
• Sometimes altered in clinical situations
• Can alter membrane excitability, e.g. in heart
2. Electrogenic pumps - Na+/K+ pump
One positive charge is moved out for each cycle.
Active transport of ions maintains ionic gradients and prevents collapse of RMP from passive movement of ions through channels.
61
Ses 5
62
Describe the properties of the action potential in nerves
• Change in voltage across membrane
• Depend on ionic gradients and relative permeability
• Only occur if a threshold level is reached
• Are “all or nothing”
• Propagate without loss of amplitude
63
Which ion cause AP to be generated
Na+ - bringing the membrane close to the Na+ equilibrium potential, ENa
64
What happens when there is depolarisation to threshold
Initiates +ve feedback
Na+ channels open —> Na+ influx —> membrane depolarises —> Na+ channels open etc
65
ARP and RRP
absolute refractory period - Na+ channels recovering from inactivated to closed state
relative refractory period - The excitability returns towards normal as the number of Na+ channels in the inactivated state decreases and the voltage-gated K+ channels close.
66
ion channel structure of K+ and Na+ notion
Na + - only need one alpha subunit with 4 repeats
K+ - need 4 subunits to come together - alpha 1 to 4
Both pore in middle
67
How do local anaesthetics work
Eg lidocaine and procaine in numbing pain
Weak bases and cross the membrane in their un- ionised form. Act by binding to and blocking Na+ channels, thereby stopping AP generation.
Open channel block - AP is firing - more block - accumulates with more use.
higher affinity to the inactivated state of the Na+ channel - block is strongest in inactivated state.
block conduction in nerve fibres in the following order:
• small myelinated axons
• non-myelinated axons
• large myelinated axons
68
How is the action potential conducted along an axon?
• A change in membrane potential in one part can spread to
adjacent areas of the axon. This occurs because of local current spread
Conduction velocity is determined by how far along these local currents can spread
• local current spread causes depolarization of part of
the axon - AP
69
Local current theory
local currents cause the action potential to propagate down the axon.
70
Factors affecting conductance velocity
A high membrane resistance • A low membrane capacitance • A large axon diameter (this leads to a low
cytoplasmic resistance)
71
Length constant
distance along an axon it takes for the initial voltage to fall to 1/e, or 37%, of its original amplitude.
Longer the better spread of AP
72
Capacitance
ability to store charge. This is a property of the
lipid bilayer. A high capacitance takes more current to charge.
cause a decrease in spread of the
local current
73
Resistance
depends on the number of ion channels open.
The lower the resistance the more ion channels are open and the more
loss of the local current occurs across the membrane, thus limiting the
spread of the local current effect.
74
myelin sheath
reduce the capacitance and increase the resistance of the axonal membrane. Myelin is formed by special cells:
• Schwann cells - these myelinate peripheral axons
• Oligodendrocytes - these myelinate axons in the CNS
Due to the reduced capacitance in the intermodal region, the local axonal current induced by an action potential at a Node of Ranvier spreads further down the axon to depolarise the next Node without firing an action potential in the intermodal region. Local current spread is faster than action potential spread over the axonal membrane surface and so nerve conduction occurs in a ‘saltatory’ manner down the nerve, greatly increasing conduction velocity.
75
Fibre diameter and conduction velocity.
Myelinated: Velocity proportional to diameter • Unmyelinated: Velocity proportional to √diameter
76
multiple sclerosis
myelin is destroyed in certain areas of the CNS - no saltatory conduction.
can lead to decreased conduction velocity, complete block or cases where only some action potentials are transmitted.
77
Explain how action potentials open Ca2+ channels
AP opens voltage-gated closed Ca2+ channels
Ca2+ entry so inc intracellular Ca
release of neurotransmitter
78
Describe some aspects of Ca2+ channel diversity and function
79
Describe events leading to transmitter release
Notion for diagram
1. Ca2+ entry through Ca2+ channels
2. Ca2+ binds to synaptotagmin 3. Vesicle brought close to membrane
4. Vesicle fuses with protein called Snare complex which make a fusion pore
5. Transmitter released through this pore
80
Explain how activation of nicotinic ACh receptors leads to an action potential in skeletal muscle
The nicotinic acetylcholine nAChR
receptor (nAChR) is a ligand gated ion channel.
It is permeable to cations.
Na+ influx - end plate depolarisation
The end-plate potential depolarizes the adjacent muscle membrane and activates voltage-gated Na+
channels, thereby initiating an action potential in the muscle fibre
81
Describe some properties of ligand gated ion channels
82
Explain how neuromuscular blockers work
Notion for graph
Blockers of nicotinic ACh receptors
Competitive block by d-tubocurarine (d-TC) - can be overcome by increasing the concentration of ACh.
Depolarizing block by succinylcholine
Succinyl choline binds to nAChR and causes depolarisation and an initial potential.
It has a longer duration of action than ACh and is not catalysed by AChE
The prolonged depolarising action of Succinyl Choline leads to VGSC remaining inactivated and the muscles kept in a state of relaxation.
83
Mayasthenia gravis
Autoimmune disease targeting nACh receptors.
Caused by antibodies directed against nAChR on postsynaptic membrane of skeletal muscle
Antibodies lead to loss of functional nAChR by complement mediated lysis and receptor degredation
Endplate potentials are reduced in amplitude leading to muscle weakness and fatigue
Patients may suffer profound weakness
Weakness increases with exercise
84
Organophosphate poisoning
• Acetylcholinesterase inhibitors that form a stable irreversible covalent bond to the enzyme
85
mAChR
produce a slower response because they are coupled to G- proteins which trigger a cascade of events in the cell.
In parasympathetic not neuromuscular
86
Ses 6
87
Extracellular signalling notion
Endocrine:
Hydrophilic 1 - Amines
Hydrophilic 2 - Peptides to Proteins
Receptors in plasma membrane
Lipophillic - Steroids - from cholesterol- Intracellular receptors
Paracrine - neurotransmitters- acetylcholine, monoamines, amino acids
Endocrine and Paracrine molecules act on RECEPTORS
Regulation is achieved by
➢ Specific signalling molecules
➢ Changes in ion concentration (e.g. Ca2+)
➢ Changes in electrical field
➢ Changes in transported substance
88
Signalling molecule targets - RITE notion
R = Receptors
4 types - KLING:
Kinase Linked Receptor(Tyrosine Kinases phosphorylate specific tyrosine residues on target proteins)
Ligand Gated Ion Channels
Nuclear /Intracellular
G-Protein Coupled Receptors
I = Ion channels VG
Binding using exogenous channel blockers results in therapeutic outcome. Eg GABA Cl - channel agonists for epilepsy
Transporters
Enzymes
Eg Aspirin binds to COX enzyme reduces prostaglandin synthesis,
DNA for chemo
89
G-proteins structure and mechanism notion
Single polypeptide chain
7-transmembrane spanning regions
Extracellular N-terminal
Intracellular C-terminal
Made up of alpha, beta and gamma subunits.
The G-protein -subunit has a guanine nucleotide binding site.
1. ligand binds with the external face of the receptor,
2. G protein binds to GPCR
3. GDP exchanged for GTP on alpha subunit
4. The α-βγ complex immediately dissociates - their affinity dec - α-GTP + free βγ subunits
5. bind with effector proteins (second messenger-generating enzymes, or ion channels).
6. α subunit GTPase activity hydrolyses GTP back to GDP.
7. α-GDP and βγ subunits then reform and become inactive.
90
What is it called when receptors have indirect activation of cellular activity
Although some receptors can directly alter cellular activity, many require “transduction” of the initial ligand binding event via other intracellular signalling components to generate a response.
91
3 “superfamilies” of cell-surface receptor
G protein-coupled receptors
(e.g. muscarinic acetylcholine receptors)
Ligand-gated ion channels (e.g. nicotinic acetylcholine receptors)
Receptors with intrinsic enzymatic activity
(receptor tyrosine kinases (e.g. insulin receptor)
92
SIGNAL TRANSDUCTIOn key points
Diversity
Specificity
AMPLIFICATION - small changes = big response
93
Diff types of G proteins notion
Gas - stimulate adenylyl cyclase
Gai - inhibits
Gaq - exert their actions on effectors other than adenylyl cyclase. preferentially Phospholipase C. hydrolysis of phosphatidylinositol 4,5-bisphosphate or PIP2.
In turn 2 secondary messengers:
Inositol 1,4,5-trisphosphate (InsP3)
Diacylglycerol (DAG)
94
Toxins Interfering with G
Cholera toxin (CTx) prevents termination of signalling by Gs
leading to long-lasting activation of downstream pathways
Pertussis toxin (PTx) ‘uncouples’ G i from mediating signal transduction events by preventing GDP being exchanged for GTP on alpha subunit. Gi signalling chronically off.
95
Therapeutic Use Voltage Gated Sodium Channels - VGSCs
Epilepsy – Use dependent block – selectively blocks VGSC
in depolarised/inactivated state e.g Lamotrigine Phenytoin
➢ Allows normal levels of CNS activity
o Local Anaesthesia –Optimal block when VGSC depolarised
inactivated state E.g. Lignocaine
• Hypertension – Multiple possible RITE targets
• Target Smooth Muscle VGCCs on membrane
➢ Reduces Ca2+ entry into smooth muscle
➢ Reduced [Cai2+] signal, decreases [Ca2+SR] release
from SR store
• Example Ca2+ blocker is Amlodopine
➢ Selective for Smooth Muscle L-Type VGCC with 2nd effect on
Cardiac VGCCs
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Transporters as Drug Targets: Treating Depression + diabetes
Selective Serotonin Re-Uptake Inhibitors – SSRIs
• Serotonin- neurotransmitter linked to depression
• After synaptic release - reuptake by Na+/5-HT co-transporter
• Depression related to low synaptic 5-HT levels
• With SSRIs 5-HT re-uptake dec + synaptic 5-HT inc
E.g. Fluoxetine (5-HT)
SGLT2 Na+ /Glucose Co-transporter Inhibitor
SGLT2 inhibitors glucose re-uptake dec so blood [glucose] dec.
Act as allosteric inhibitors on external face of SGLT2 - Changes conformational state to dec re uptake
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Enzymes as Drug Targets: Antihypertensives
ACE Inhibitors - competitive
reduce Ang. 1 conversion ➔ BP dec
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Tyrosine Kinase Transduction -Insulin as Ligand
Transduction Steps
• Step 1 – Insulin as agonist binds with monomer RTKs
• Step 2 –Monomers form the active state dimer
• Step 3 –Each monomer in the activated dimer then
autophosphorylates the other
• Step 4 – Complete phosphorylation of the RTK
dimer makes it fully active
As each RTK site can bind different transducer
proteins - ONE ligand can set up multiple signalling
pathways - phosphorylation cascade.
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Main Effectors and Second messengers
Adenylyl Cyclase
hydrolyse cellular ATP to generate cyclic AMP.
Cyclic AMP interacts with protein kinase A.
PKA then in turn phosphorylates a variety of other proteins to increase or decrease their levels of activity.
increased glycogenolysis and gluconeogenesis in liver and increased lipolysis in adipose tissue. It can also cause relaxation in a variety of types of smooth muscle and positive inotropic and chronotropic effects in the heart.
Phospholipase C
hydrolysis of PIP2 = IP3 and DAG
IP3
IP3 - interacting with specific intracellular receptors on ER ( inositol triphosphate receptors - IP3R) to allow Ca2+ to leave lumen of ER and enter the cytoplasm.
The hydrophobic DAG stays within the lipid bilayer and interacts with Protein Kinase C.
Smooth muscle contraction via alpha 1.
M3 - bronchoconstriction - ach
contract gastrointestinal and genito-urinary smooth muscle.
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Others
cyclic GMP
cGMP-dependent protein kinase (PKG)
Ca2+
Ca2+ or Calmodulin-dependent protein kinase (CaM-Kinase)
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Limiting signal amplification
agonist-receptor dissociation
PK phosphorylate membrane receptor and prevent it activating further G proteins
Intrinsic GTPase
high activities of enzymes which metabolize second messengers
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Signalling pathway - Inotropy in the heart
Normal levels of adrenaline and sympathetically released NA interact with beta 1 adrenoceptors
Gs receptor
Inc cyclic AMP
PKA phosphorylate and activate the VOCC (voltage operated ca channel)
Calcium induced calcium release - inc ca influx causes inc release from ER - binds to ryanodine receptors which causes release.
Inc contractility
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Smooth muscle contraction
SNS NA and normal A interact with alpha 1 adrenoceptors on vascular smooth muscle.
Gq pathway
Calcium-calmodulin complex activates MLCK which phosphorylates the regulatory myosin light chain - myosin head active.
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neurotransmitter release
G protein-coupled receptors located pre-synaptically.
Pre-synaptic μ-opioid receptors
stimulated, either by endogenous opioids, or by analgesics such as morphine, to couple to Gαi proteins.
The Gβγ subunits liberated and interact with VOCCs to reduce the entry of Ca2+ through these channels.
Dec neurotransmitter release from pre-synapse.
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R KLING ITE
Nuclear notion
• Endogenous Ligands include:
➢ Steroids Cortisones Testosterone Oestrogen Progesterone
➢ Thyroid T 3 Hormones
➢ Vitamins D and A/Retinoic Acid
Structure:
N - terminal – Transcription domain
DNA Binding Domain - Binds at DNA sequence Hormone Response Element - HRE
Hinge Region – Flexible - allows dimerisation with other NRs
Ligand Binding Domain binds ligand
➢ Once bound changes conformation of NR
➢ Allows start of approach sequence to bind with DNA
C - Terminal Region
once ligand binds loses Inhibitory Protein
Increase/decrease Gene Transcription
Inflammatory Conditions - Allergies Asthma, Arthritis
Eg Dexamethasone
Oral Contraceptives
Immune Suppression after Organ Transplant
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Ca homeostasis how is it regulated
• Whole body Ca2+ homeostasis is regulated via
▪ Intestinal Ca2+ uptake
▪ Ca2+ reabsorption in the kidneys
▪ Bone calcium regulation
• These processes are under endocrine control
▪ Ca2+-sensing receptors in the parathyroid gland
▪ Parathyroid hormone
▪ 1,25-dihydroxyvitamin D3
▪ Calcitonin
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R (KLING) ITE
LI for ligand gated ion channels
Notion for table and nicotinic Ach receptor and GABA structure
Nicotinic Ach receptors
Anionic pore residues for cations (Na+ K + Ca2+ )
Cationic pore residues for anions (Cl-)
ACh ligand needs to bind at two sites sitting
Two inward ‘kinks’ in α sub units form pore gate
Binding ACh causes conformational change in both α sub units - ‘twist’ so side gate opens - current flows.
nAChR – PNS - End Organ Muscle Relaxants
Agonists = Succinyl Choline (2 Ach molecules) - depolarising blocker in surgery –
short acting.
Antagonists = Non depolarising blockers - range of duration eg Pancuronium - greater control.
GABA A receptors
Pentameric subunits
Selective for Cl-
Two GABA ligands need to bind at sites between both αβ- subunits to open central pore.
Modulates (reduces) excitatory input so it is inhibitory.
GABA A receptor allosteric modulators enhance GABA action – not employ agonists or antagonists eg Benzodiazepines. They act between α/gamma subunits – inc Cl- current so hyperpolarise which offsets excitatory input. Can be uses as muscle relaxants, anaesthesia or for epilepsy.
Other drugs/alcohol also allosterically modulate.
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Ses 8 ans
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Transmitters in ANS other than cholinergic or adinergic
Other transmitters ( known as NANC - “non- adrenergic, non- cholinergic” - transmitters) are also important in certain situations.
Often co-released with either ACh or NA (co- transmission).
Examples of NANC transmitters include: ATP; serotonin; nitric oxide; several neuropeptides e.g. neuropeptide Y.
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• Outline the major anatomical and neurochemical divisions of the ANS • Recall the origins of the sympathetic and parasympathetic divisions of the ANS from the spinal column • Recognise that ACh and Noradrenaline are the primary
neurotransmitters used by the ANS notion
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SNS exceptions
Some sympathetic post-ganglionic neurons are cholinergic not noradrenergic
» those innervating sweat glands, hair follicles (piloerection)
» they release ACh that acts at muscarinic ACh receptors
Sympathetic postganglionic neurons in the adrenal glands:
• Are differentiated to form neurosecretory chromaffin cells
• Chromaffin cells can be considered as postganglionic sympathetic neurons that do not project to a target tissue
• Instead, on sympathetic stimulation these cells release adrenaline into the bloodstream
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Parasympathetic receptor actions and How the above complements the arteriolar response to exercise in Skeletal Muscle finish. Also use QISS QIQ
bradycardia - SA node - M2
reduced contraction - AV node - M2
Smooth muscle
Relax arterioles
bronchial contraction - lungs - M3
increased secretion GI tract - M3
ciliary muscle and iris sphincter contraction - eye -M3
Glandular
increased sweat/salivary/lacrimal secretion - M1/M3
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Sympathetic receptor and effects How the above complements the arteriolar response to exercise in Skeletal Muscle finish. Also use QISS QIQ.
tachycardia - SA node -β1
positive inotropy - ventricles - β1
Smooth muscle
arteriolar contraction/venous contraction - α1,β2
bronchiolar - β2
radial muscle contraction - β2
Glandular
increased (viscous) secretion salivary - salivary glands
Kidney
renin release
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sensory inputs to the ANS
Sensory neurones sense levels of CO2, O2, nutrients, arterial pressure in the blood.
CSF and area postreama detect toxins.
Project to second order neurones in nucleus tract is solitarus in medulla oblongata.
Chemoreceptors on Carotid body also sense CO2, O2, pH of blood. Relay info to CNS via glossopharyngeal nerve.
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drugs acting on signal termination at cholinergic synapses
Treated with atropine - anti-choligernic
Ach degradation
acetylcholine —> acetate + choline
Needs cholinesterase (AChE).
covalently-modify this, to irreversibly deactivate the enzyme and increase acetylcholine levels - nerve agents eg novichok.
In organophosphate poisoning, organophosphate eg parathion inhibits esterase so there is tetany.
Prolonged muscarinic (PNS) causes SLUDGE.
Salivation
Lacrimation
Urination
Defecation
GI problems
Emesis
SLUDGE also caused by Ingestion of “magic” mushrooms
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Outline key points in cholinergic transmission and age
Synthesis
transported into synaptic vesicles by an indirect active transport
Released
Degradation in few msecs
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Recall the effects of cholinergic agonists and antagonists
M Agonists - pilocarpine used to treat glaucoma (inc intraocular pressure).
Also dec atrial tachycardia.
Side effects due to lack of selectivity - SLUDGE.
M Antagonists - tiotropium
used to treat asthma and chronic obstructive pulmonary disease (COPD).
Oxybutynin used to treat overactive bladder.
Hyoscine decreases bronchial and salivary secretions, reduces any bradycardia induced by the anaesthetic.
nAChRs antagonists- autonomic ganglia and somatic neuromuscular junction differ in structure.
drugs have actions selective to autonomic ganglia e.g. trimethaphan - used in hypertensive emergencies.
pancuronium - muscle paralysis in anaesthesia- LGIC blocker.
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Outline key points in adrenergic transmission notion
Tyrosine to DOPA to dopamine to NA. Rate-limiting enzyme is
tyrosine hydroxylase.
Noradrenaline is released by Ca2+-dependent exocytosis.
Interacts with adrenoceptors in the post-synaptic membrane.
NA interacts with pre-synaptic adrenoceptors to regulate
processes within the nerve terminal.
Rapidly removed from the synaptic cleft by noradrenaline transporter proteins:
1. NET uptake 1 - re-uptake into the pre-synaptic terminal by a Na+-dependent, high affinity transporter.
2. Uptake 2 - lower affinity, non-neuronal mechanism.
Within the pre-synaptic terminal NA not taken up into vesicles by H+ ATPase is metabolised by 2 enzymes:
monoamine oxidase (MAO) + catechol-O-methyltransferase (COMT)
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Recall the effects of adrenergic agonists and antagonists
β2-adrenoceptor-selective agonists (e.g. salbutamol) are used in asthma to oppose bronchoconstriction.
Selective β1-agonists (e.g. dobutamine) can cause positive inotropic and chronotropic effects which may be useful in treating circulatory shock - however, all β1-agonists are prone to causing cardiac dysrhythmias
Selective α1-agonists (e.g. oxymetazoline) are used as
nasal decongestant.
Selective α2-agonists (e.g., clonidine) can be used as antihypertensive
agents.
α1-adrenoceptor-selective antagonists (e.g. doxazosin) +
β1-adrenoceptor-selective antagonists (e.g. atenolol) - treat
cardiovascular disorders, including hypertension.
Possible unwanted side-effects include bronchoconstriction (particularly using non- selective β- adrenoceptor antagonists, bradycardia, cold extremities, insomnia and depression.
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Other adrenergic drugs
IASAs
Eg amphetamine
weak agonists
transported into the adrenergic terminal by Uptake1
cause noradrenaline to leak from the vesicle
displaced noradrenaline can leak into the synaptic cleft
inhibits tyrosine hydroxylase
Uptake 1 Inhibitors - tricyclic antidepressants e.g. amitriptyline - tachycardia and cardiac dysrhythmias.
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Ses9
122
reversible competitive antagonism
irreversible competitive antagonism
non-competitive antagonism
R - Greater [antagonist] = greater inhibition
IC50 = Concentration of antagonist giving 50% inhibition
Tell you about strength of agonist as well.
cause a parallel shift to the right of the agonist concentration-response curve.
Eg naloxone
Binds at orthosteric site
I - antagonist dissociates slowly or not at all
parallel shift to the right of the agonist concentration-response curve and at higher concentrations suppress the maximal response. Binds at orthosteric.
In a Pheochromocytoma tumour releases excess adrenaline - cause vasoconstriction as it binds to alpha 1 receptors- high blood pressure headache sweating panic attacks
phenoxybenzamine cannot be out competed by adrenaline.
N -
negative allosteric modulation)
Maraviroc - AIDS
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molarity
Molarity (M) = g/L / MWt
Conc of drug molecules around receptor
MWt - molecular weight
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Agonist and antagonist
Agonist - binding governed by affinity - strength of interaction- cause conformational change (intrinsic efficacy) activates receptor.
Antagonist- just has affinity - block receptors - prevents action of agonist
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Quantify interaction (BINDING) - Kd
Plot ligand that’s bound to receptors vs. ligand concentration - y vs x
Bmax = receptor no/binding capacity
Kd- index of affinity - dissociation constant
amount of conc required to occupy 50% of available receptors.
Lower Kd = higher affinity
Measure binding by radioactive/fluorescent ligands
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Affinity importance example
morphine or heroin overdose (respiratory depression- death)
naloxone used to treat overdose
- high affinity antagonist of m-opioid - out competes opioid receptors
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drug POTENCY
Draw conc-response curve (measure response from change in cell behaviour or signalling pathway)
Measure concentration giving 50% of the maximal response
EC50 = effective conc giving 50% of max response
This is drug potency
Only for agonists as it depends on affinity and intrinsic efficacy.
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concentration & dose
Conc - know conc of drug at site of action
Dose - unknown
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selectivity/specificity?
Beta 2 adrenoceptors are a target in asthma that provide functional antagonism of contraction
It would inc force and rate of contraction of heart as it has beta 1.
Salbutamol has enhanced selectivity for beta 2 so affects lungs more.
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Spare Receptors
increase sensitivity/potency - allow responses at low concentrations of agonist
Example:
Full response = 10,000receptors
No of receptors = 10,000 - no spare
Requires 100% occupancy
Kd = 1m
Requires = 10m
But
If 20000 then only need 1m
With EC50 ≈ Kd , this is taken as evidence that there were no spare receptors
Also influences max response
Eg if 5000 receptors only cannot have max response.
Receptor no dec with high activity - down regulation and vice versa.
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Partial agonists
lower intrinsic activity - lower Emax - evoke responses that are lower than max response of full agonist.
allow a more controlled response
can act as antagonist if high levels of full agonist - prevent full response
Eg
Buprenorphine will inhibit the effect of heroin: a partial agonist can provide antagonism
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Intrinsic activity
Gives max response
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Ligand
Substance that binds to receptors and causes a response
134
Why is there diff in EC50 and Kd - check
Due to spare receptors giving lower Kd
Or
Signal amplification can cause diff
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What is binding at same site as ligand called
Orthosteric
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Ses 10
137
Recognise main routes of drug administration into the body
Enteral or parenteral
Enteral - oral, sublingual, rectal
Parenteral - IV, Subcutaneous, Intramuscular, Intranasal
Transdermal, Inhalational
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Where and why does drug absorption happen
Gastric mucus layer prevents absorption in stomach.
Happen in SI - large SA due to villi and microvilli and valves of Kerckring, churned to max digestion, weakly acidic.
Typical transit time = 3-5hrs
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mechanisms of drug absorption
Passive diffusion - lipophilic drugs eg steroids and drugs that are weakly ionic will be taken up. Protonated acid (otherwise will be H+ and anion and cannot cross) and unprotonated base can cross.
facilitated diffusion or secondary active transport - SLC - OATs and OCTs - move negatively charged molecules against electrochemical gradient.
Eg penicillin is -ve and co-transport with H+ ions.
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Factors Affecting Drug Absorption in GI
• GI length /SA
• Drug lipophilicity / pKa
• Density of OAT/OCT expression in GI
• Blood Flow: Increase post meal – drastically reduce shock
• GI Motility: Slow post meal - need time for absorption
• Food /pH: Food can reduce/increase uptake. First pass metabolism - phase 1 and 2 (cytochrome P450s and conjugating) enzymes metabolise drugs
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Bioavailability
Fraction of a defined dose which reaches its way into a specific body compartment - CVS
Amount of drug reaching systemic circulation/ total amount of Drug Administered
Denominator = Total Amount of Drug Administered by the Intravenous (iv) Route.
Oral bioavailability = F = total drug from IV (AUCiv) / drug administered by oral route (AUCoral)
F = AUCoral / AUCiv
Drug administered via intravenous bolus is said to have 100% bioavailability
• For other routes referenced as a fraction of i .v.
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factors affecting distribution of a drug
Lipophilicity
- more lipophillic means more move out of blood plasma into tissues.
If -ve then going into tissues depends on pH of tissue, pKA of drug, OAT/OCT density.
degree to which it binds to plasma proteins
Binds to albumin - Determines conc of free unbound drug that can exert effect. Competition for binding site
affects free plasma conc .
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Volume of distribution - Vd
3 basic fluid compartments- plasma, interstitial and intracellular
Vd = drug dose/ [plasma drug]
Units = L/kg
Increasing Penetration by Drug into Interstitial and Intracellular Fluid Compartments Leads to
Decreasing Plasma Drug Concentration
Increasing Vd
Changes by:
Hypoalbunimea – affect protein binding
Changes in body weight
Renal failure
Drugs with narrow therapeutic ratio
Pregnancy + pead + geriatrics
Cancer
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Model of drug movement notion
145
Drug Metabolism - general
Drug Metabolism largely takes place in Liver via Phase 1 and II enzymes.
Lipophillic drugs can diffuse out of renal tubules into plasma so these enzymes inc ionic charge to enhance renal elimination
146
Phase 1
carried out by Cytochrome P450 Enzymes - generalists
metabolise very wide range
of a large number of molecules
Inc ionic charge
Possible Outcomes:
Metabolised drug eliminated directly
go onto Phase II
Some ‘pro-drugs’ activated by Phase I metabolism to active species (Codeine to Morphine) Some active drugs are metabolised to produce another active drug (Fluoxetine to Norfluoxetine)
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Codeine to Morphine
Codeine metabolised by CYP2D6 to Morphine • Morphine x 200 K d
affinity of Codeine for Opioid µ-Receptor
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Phase 2
mainly cytosolic enzymes
Phase II metabolised drugs further increased ionic charge to further enhance renal elimination.
Do this by conjugation which catalyses addition larger charged groups eg Sulphation, N-Acetylation, Glucorinadation, Glutathione conjugation. Enhance hydrophilicity.
Inc kinetics (works faster)
149
Factors Affecting Drug Metabolism
Age (Variable patterns in paediatric groups - reduced in elderly) •
Sex (gender differences drugs e.g. alcohol metabolism slower in women) •
General Health/Dietary/Disease - especially Hepatic Renal CVS (HRH acronym) - Decreased Functional Reserve
CYP450s: Induction and Inhibition and Genetic Factors •
Other drugs (Rx/OTC) can induce or inhibit CYP450s •
Genetic variability – polymorphism or non-expression affects CYP450s
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Induction
increased transcription, translation or the slower degradation of the enzyme due to the drug.
more rapid elimination, of the therapeutic substrate.
more of the enzyme to deal with metabolising and eliminating the drug - dosing might have to change.
important for drugs that induce their own metabolism, such as carbamazepine. It is metabolised by CYP3A4, which it also induces. This means the levels of this drug must be carefully monitored in the first few months of its prescription for treating epilepsy.
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Inhibition
drugs can act as inhibitors of CYP450 enzymes
can result in elevation of drug plasma levels and a risk of toxic side effects of the therapeutic drug.
Inhibition of CYP450s can occur both via competitive (two drugs being metabolised at the same site ) and non-competitive inhibition ( inhibitor binding at a separate site).
In contrast to induction, the onset of inhibition would depend on the pharmacokinetic profile of each drug and be evident in 1-2 days compared to 1-2 weeks.
Grapefruit Juice inhibits CYP 3A4 • CYP 3A4 metabolises. Verapimil used to treat high blood pressure (BP) • Consequence can be much reduced BP and fainting.
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Genetic Factors
• CYP2C9:
Not expressed in: 1% Caucasians; 1% Africans
• Metabolises NSAIDs, Tolbutamide, Phenytoin,
• CYP2C19: Not expressed in: 5% Caucasians; 30% Asians
• Metabolises Omeprazole, Valium, Phenytoin
CYP2D6 not expressed: 7% Caucasians
CYP2D6 is Ultrarapid : 30% East Africans • Example of Polymorphism • Metabolises Codeine, TCAs
Need to consider safety/efficacy if not metabolised /rapidly metabolised
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Drug Elimination
