Integrated physiology and pharmacology Flashcards
What percent weight of the cell membrane is lipid?
42%
What percent weight of the cell membrane is protein?
55%
What are the Na and K concentrations of the Extracellular fluid?
High Na concentration (100-140mM)
Low K concentration (5mM)
What are the Na and K concentrations of the Extracellular fluid?
High Na concentration (100-140mM)
Low K concentration (5mM)
Is the extracellular concentration of Ca high or low?
High
Name 3 categories of transporters which lie in the membrane.
Carriers
Pumps
Channels
What is the bicarbonate concentration outside the cell?
And what is its function?
25mM. Acts as a buffer.
What is the name for a polymer comprising of 4 monomer units and give an example.
Tetramer. Na/K ATPase, comprised of 2 alpha and 2 beta subunits
How does the Na/K ATPase pump maintain a low intracellular Na concentration?
By pumping out 3Na and taking in 2K
Name two factors influencing passive transport.
Potential
Concentration
How many genes are required to form the Na/K ATPase and why?
- The Na/K ATPase is a tetramer therefore it consists of 4 subunits. These are 2 alpha and 2 beta subunits. Different genes are required to form both.
What is the turnover for carrier proteins?
10(2) to 10(3) per second.
What is the name of a carrier that transports one molecule in one direction?
Uniporter
What is the name of a carrier that transports two molecules in one direction?
Symporter (Cotransporter)
What is the name of a carrier that transports two molecules in opposite directions?
Antiporter (exchanger)
Why is the sodium potassium pump described as an electrgenic transporter?
Because when the pump moves out 3Na and in 2K there is a net movement of charge (there is an overall loss of 1 positive charge from the cell during every exchange.)
Name an sodium potassium pump antagonist and describe how it works.
Digoxin. Digoxin binds to the enzyme in the extracellular part. This is the area that, when phosphorylated, binds to potassium. This can cause hyperkalemia as the extracellular K concentration increases as less is being taken into the cell.
Why are channel proteins conductive?
There is a net movement of charge as ions pass from the extracellular matrix, through channel proteins, to the intraxellular matrix. This creates a current. Therefore, when open, channels are conductive whilst when closed, they’re non-conductive.
What is the turnover for Channel proteins?
10(6) to 10(8) ions per second.
Are channel proteins selective or non selective?
Both. They’re selective to Na, K, Ca and CL. They’re non-selective to everything else.
Describe the cell membrane attached patch clamp technique.
This method is used to measure the electrical properties of a small portion of the cell membrane.
Initially a glass pipette with a very small opening ( roughly 1 micron) is used to make a very tight suction contact with a tiny part of the cell membrane. This contact is so tight that no ions are able to pass between the pipette and the membrane. The pipette initially contains a salt solution (ionic)
As a result, all of the ions which enter the piptte will be from a channel protein in the cell membrane. Thus, this tiny space will express a current. This current can be measured using an ultrasensitive electronic amplifier (Electrode) connected to the pipette.
Who developed the patch and clamp technique? and when?
Nehr and Sakman in the 1980s
Name a disadvantage to the cell-attached patch clamp technique.
The cell can rupture over time.
Why is whole cell patch clamp better than cell attached?
Cell attached only provides a current recording for a select region of the cell membrane, this figure is then multiplied (x) to give a representation of the current expressed from every ion channel in the cell.
Whole cell however provides the current for the entire cell membrane, thus making it more accurate compared to cell attached.
In the equation I = N.P0.g.(Vm-Ei). What does the I represent?
Total current carried by population of channels.
In the equation I = N.P0.g.(Vm-Ei). What does the N represent?
Number of channels
In the equation I = N.P0.g.(Vm-Ei). What does the P0 represent?
Open probability. A P0 of 1 would mean that the channels are always open. The higher the P0 the higher the current.
In the equation I = N.P0.g.(Vm-Ei). What does the g represent?
Single cell conductance. This is the constant.
In the equation I = N.P0.g.(Vm-Ei). What does the Vm represent?
Membrane potential
In the equation I = N.P0.g.(Vm-Ei). What does the Ei represent?
Equilibrium potential ion i. This is the membrane potential and the ion potential. The bigger the driving force of ion movement, the bigger the current.
Name 3 types of chemical buffer in the body
Bicarbonate buffer
Phosphate buffer
Protein buffers.
What is a physiological buffer?
A physiological buffer is a system that controls a pH by controlling the body’s output of acids, bases or CO2.
Give 2 examples physiological buffers.
Urinary system - this is the best system as it buffers the greatest quantity of acid however this can take several hours or days to occur.
Respiratory system - this can buffer much quicker than the Urinary system but it cannot alter the pH as much.
What is a chemical buffer?
A system that acts to minimise changes in pH by either accepting or donating protons.
A mixture formed of a weak acid and weak base
What two factors determine the amount of acid or Base that can be neutralised?
- the concentration of the buffer
- the pH of their working environment
Name a weak acid
H2CO3
Name a strong acid
Hydrochloric acid (HCl)
Name a weak base
HCO3
Name a strong base
OH
What is a buffer power?
The amount of strong Base that must be added to a solution in order to raise the pH by a given amount.
Or
the amount of acid that must be added to a solution in order to lower the pH by a given amount.
How is fluroscene used in a technique to study intracellular pH?
Fluroscene is proportional to intracellular pH so that emission increases with pH..
As a result of this calibration is done at the end of the experiment to correspond certain emission intensities to their subsequent pH.
How are fluroscene pH measurements calibrated?
A proton iontophor is added to the cell, this allows the cell to become the same phone as the bath it’s placed in. I.e if the bath is ph6 then the cell will become ph6. This allows us to calibrate the emission produced with the pH being analysed.
What 3 factors are involved in pH control?
Buffering, acid extrusion and acid loading.
How does acid extrusion occur and what proteins are involved?
Occurs at an Na/H exchanger antiport protein.
Under normal conditions Na is transported out of the cell whilst H is transported into the cell. Both are transported down their concentration gradients.
The Na concentration gradient is maintained by the Na/K ATPase
What is a setpoint I regards to acid extrusion?
A set point is essentially an on and off switch.
What the pH increases and the H concentration decreases below a certain set point the exchanger is off (so at alkaline pHs the exchanger is inactive)
So as the pH decreases (becomes more acidic), it switches on.
What is almost allomsteric modification of function in regards to the Na/H exchanger?
This is the process by which protons, other than the one being transported, bind to the exchanger. This leads to a conformational change in the structure of the protein which in turn increases it’s activity.
Give 2 example of a protein involved in acid extrusion?
NHE1 found in the basolateral membrane and is involved in the regulation of pH and cell volume control.
NHE3 found in the apical membrane if the proximal tubule and is involved in bicarbonate reabsorption.
What drug inhibits NHE1 and how does it work?
NHE1 becomes inhibited by ‘low’ concentrations of Amiloride and it’s analogue EIPA.
Give two clinical uses for amiloride.
Blocks Na/H antiport error proteins.
Used to act on the heart to minimise reaper fusion injury in ischemic attacks.
Used to block antiport proteins on the apical surfactant of proximal tubule cells in the nephron. This abolishes more than 80% of the action of angiotensin II on secretion of H in proximal tubule cells.
What is Enac?
Epithelial sodium channels which mediate sodium reabsorption in the aldosterone sensitive distal part of the nephron and collecting duct of the kidney.
What regulates Enac activity?
Aldosterone, angiotensin II, insulin and vasopressin.
How much alimoride is required to inhibit Enac?
50 micro Molar
How much alimoride is required to inhibit Na/K ATPase?
1 milli Molar.
How does acid loading occur and what proteins are involved involved?
Occurs as a result of Cl/HCO3 exchanger.
Under normal conditions the Cl moves into the cell whilst the HCO3 moves out of the cell.
Turns on in alkaline conditions and turns off in acidic conditions.
What family is the Cl/HCO3 antiport protein in?
Anion exchanger (AE) family.
When is there an exception in the function of the Cl/HCO3 antiport protein?
In red blood cells, during the hamburger effect whereby Cl is released and HCO3 is taken into the cell.
What are cardiac glycosides?
Organic compounds containing glycoside (sugar) that act on the contractile force of the heart.
Name 2 cardiac glycosides that inhibit the Na/K pump.
Digoxin
Ouabain.
Give two factors involved in the tole of the Na/K pump.
Electrogenic transport of 3 +ve charges out of the cell and two +ve charges into the cell produces a net effect making the inside of the cell more negative.
More importantly the accumulation of K inside the cell establishes a greater and greater concentration gradient between that of the outside, thus increasing the driving force for K to leave the cell through K channel proteins - making the cell more negative.
Because the energy expenditure is so high to generate the concentration gradient produced from the Na/K pump, the movement of Na into cells is generally only through pathways with physiological significance - give two examples.
In the collecting duct of the nephron. Amiloride sensitive channels are on the apical membrane whereas the Na/K pump is known the basolateral. Rather than just recycling the Na this arrangement allows directional transport .
In excitable cells the Na entry produces decolonisation leading to the action potential being produced. The Na is recycled by the pump but an important physiological process is occurring.
Under normal conditions, what is the extracellular Ca concentration?
1mM (1000000nm)
Under normal conditions, what is the intracellular Ca concentration?
100nm
Why is Ca regulation important?
Can is an important second messenger involved in many signalling pathways.
Give an example of when Ca acts as a second messenger.
In pancreatic acinar cells. Acetylcholine, gastrin (CK-B) and substance Park Lloyd act as primary messengers which cause the release of cellular Ca. The Ca then acts as a secondary messenger to increase cyclic GMP and increase enzyme secretion.
The inward gradient of Na is 10 fold whilst the gradient for Ca is 10000 fold, how does the Na/Ca exchanger keep Ca concentrations low?
The exchanger is electrogenic in that it produces a slight change in the electrical potential of the cell. This occurs as a result of its stoichometry in that the exchanger brings in 3Na for every 1 Ca.
This causes the Na gradient to become magnified. The effect of the q0 fold gradient is cubed.
What gene family is the Na/Ca exchanger part of?
SLC8 family.
What super family is the SLC8 (Na/Ca exchanger) gene family part of?
CaCA superfamily.
What are the forms of Na/Ca exchangers called in mammals? (3 forms)
NCX1-3
What family are Ca ATPases and the Na/K ATPase part of?
P-type ATPase family
What 3 types of Ca ATPase do cells contain?
PMCA - Plasma membrane calcium pumps
SERCA
SPCA
What is a PMCA type calcium pump?
A plasma membrane calcium pump. This pump, alongside the Na/Ca pump, act to keep intracellular Ca concentrations low.
What are the SERCA type calcium pumps?
These are calcium pumps found on the sarcoplasmic or endoplasmic reticulum membranes.
What is the function of SERCA Ca pumps?
They reside in the sarcoplasmic reticulum of muscle cells. It is a Ca ATPase thatmoves calcium from the cytosol of the cell to the lumen of the sarcoplasmic reticulum during muscle relaxation. As this is an ATPase, ATP is hydrolyzed.
What are the SPCA type calcium pumps?
Ca pumps located on the Golgi apparatus.
What is the function of the SPCA type calcium pumps?
They supply the golgi apparatus with calcium (Ca) and Manganese (Mn) necessary for the production and processing of secretory proteins.
Give an example of when a SPCA calcium pump is used.
In the lactating mammary gland, SPCA seems to be the primary pump responsible for supplementing the milk with high (60-100mM) of calcium.
Name 4 types of plasma membrane pathways involved in Ca signalling.
VOCC - Voltage operated calcium channels
ROCC - Receptor operated calcium channels
MACC - Mechanically activated calcium channels
SORR - Store operated calcium channels.
Give an example of where voltage operated calcium channels (VOCC) are found.
In excitable cells. They’re activated by depolarization.
Give an example of where receptor operated calcium channels (ROCC) are found.
In secretory cells and nerve terminals which are activated by the binding of an agonist.
Example. ndma receptors. A glutamate of glycine agonist binds to the receptor. This activates the channel and allows positively charged ions to pass through the membrane.
What are Mechanically activated calcium channels (MACC)?
Channels found in many cells which respond to cell deformation. These would include stretch mediated channel proteins.
What are store operated calcium channels (SOCC)?
Channels which are activated following the depletion of calcium stores.
Name the two classes of calcium channels in the store membranes.
IP3 receptors
Ryanodine receptors.
Describe IP3 receptors.
A channel activated through the binding of IP3. This type of receptor is present on most cells types.
Describe Ryanodine receptors.
Low concentrations of ryanodine activate the receptor whilst high concentrations inhibit. Tends to be found in excitable cells.
What is the natural activator of ryanodine receptors?
cADP ribose.
What can stimulate ryanodine receptors other than the natrual activator cAMP ribose?
Caffine.
What is the name of the calcium current produced once SOCCs have been opened?
Calcium-release-activated-calcium current (ICRAC)
Name 2 proteins involved in re-establishing the lost calcium to the endoplasmic reticulum.
ORAI1 and STIM1
Name 3 potential mediators of ICRAC
- Phospholipase A2 Beta
- Nicotinic acid adenine dinucleotide (NAADP)
- STIM1 Protein
Why is it important to keep intracellular [Na] low in the epithelial cells of the thick ascending limb (loop of Henle)?
If intracellular [Na] was to increase then NaCl reabsorption is inhibited. The transepithelial osmotic gradient becomes dissipated resulting in diuresis and increased Na and Cl in the urine.
Define anatomical dead space.
The volume of the conducting airways.
What volume of air does anatomical dead space occupy?
Approximately 30% of inspired air (150ml)
Define physiological dead space.
The volume of the lungs that doesn’t participate in gaseous exchange. This is equal to the conducting zone + non-functional areas of the respiratory zone.f
Define expiratory reserve volume.
The additional amount of air that can be expired from the lungs by determined effort after normal expiration.
Define residual volume.
The amount of air remaining in the lungs after fully exhaling.
What is FRC?
The sum of expiratory reserve volume and residual volume - approximately 2400ml in an 80kg average sized male.
What is pulmonary compliance?
A measure of the lung’s ability to stretch and expand.
Give an example of a condition with a low lung compliance.
Pulmonary fibrosis. The paranchyma surrounding the lungs becomes more rigid, thus reducing the lungs ability to stretch and extend. Involves difficulty inspiring due to this.
Give an example of a condition with a high compliance.
Emphysema. Involves difficulty expiring due to the loss of elasticity of the lung tissue - reducing elastic recoil.
What happens when the volume is less than FRC?
There is a smaller volume in the lung so the forces favoring elastic collapse are low. The forces of the chest expansion are favored so the system expands.
What happens when the volume is higher than FRC?
The elastic forces in the lung favoring collapse are higher. The forces for chest expansion are now less favored (small) so the overall system collapses.
Give two clinical uses for Amiloride.
Amiloride blocks the H/Na exchanger which is part of acid extrusion. Amiloride is used to block these antiporters in heart muscle to minimise reprusion during ischemic attacks.
Also used to act on antiporters on the apical surface of proximal tubule cells in the nephron. Amiloride blocks 80% of Angiotensin II on the secretion of H, helping retain H
Give an example of an Na/H exchanger and describe its topography.
NEH1.
Has 12 transmembrane spanning domains.
Loop between 4-5 is linked to Na transportation
Loop between 6-7 linked to H extrusion.
Long intercellular C terminus with lots of potential binding regulatory sites.
Sensitive to calcium calmodulin which causes it activation.
What Na/H exchanger is found on the basolateral membrane and which is found on the apical?
NHE1 - basolateral
NHE3 - Apical
How many subtypes of the Cl/HCO3 exchanger are there?
4 AE1-4
What inhibits the Cl/HCO3 exchanger?
DIDS - Stibene derivative drug.
What is the Cl/HCO3 exchangers role in RBCs?
AE1 is involved in complexes with Carbonic anhydrase and Aquaporin 1. They help optomise CO2 transport in the blood - hamburger shift.
What is the Equilibrium position in the lungs?
This is where the collapsing force of the lung is equal to the expanding force of the chest. Palv=Patm giving FRC
What happens when volume is less than FRC?
Lung forces are less than that of chest, favouring expansion. (happens as you breath out, leading to breathing back in)
What happens when volume is higher than FRC?
Lung forces are higher than that of the chest, favouring collapsig (happens progressively as you breath in, leading to breathing back out)
What happens to compliance as volume increases?
At low volumes, the lungs have a high compliance. At higher volumes however, the lungs have a lower compliance.
What 2 factors contribute to the elastic recoil of the lungs?
Anatomical component - Elastic nature of cells and extracellular matrix
Elastic recoil due to surface tension generated at air/fluid interface.
In an experiment with a cat lung, what happens in regards to changes in volume when the lungs are filled with fluid and when they’re filled with air.
When filled with water (saline), very small pressure changes are required to increase the volume of the lungs.
When filled with air very little pressure causes very little changes in volume due to the surface tension at the air/fluid interface, once the pressure is high enough to overcome this tension, then the volume begins to increase.