ICCP S5 ATP-dependant Pumps And Ion Exchangers

Question 1

What are the 2 broad functions of Na K ATPase?

Answer 1

Forms Na+ and K+ gradients necessary for electrical excitability of cells and contributing 5mV of resting potential.
Drives secondary transport by setting up electro chemical gradients that can be utilised by symporters/ antiporters to facilitate diffusion.

Question 2

What does secondary active transport control?

Answer 2

pH
Cell volume regulation 
Ca2+ concentration regulation 
Na+ Absorption in epithelia 
Nutrient uptake - eg glucose and amino acid symporter into enterocytes from chyme.

Question 3

What are the 4 main control mechanisms for Intracellular [Ca2+] control?

Answer 3

SERCA
PMCA
Ca2+ uniporter
NCX

Question 4

Describe properties of PMCA and SERCA.

Answer 4

Both high affinity low capacity

Both actively transport Ca2+ out of cytosol by moving H+ into cytosol.

Question 5

Describe properties of Ca2+ uniporter.

Answer 5

High affinity low capacity

Facilitates diffusion of Ca2+ into mitochondria if [Ca2+] rises too high.

Question 6

Describe properties of NCX.

Answer 6

Secondary active transporter
High capacity and low affinity
Pumps out a Ca2+ for 3 Na+ in.
Electrogenic because 2+ leaves but 3+.

Question 7

How do the roles of PMCA and NCX differ in Ca2+ concentration regulation?

Answer 7

PMCA is used to correct small changes in concentration that occur

NCX is used to correct changes that occur after large influx of Ca2+ ions.

Question 8

What role does NCX play in cell toxicity during ischaemia and reperfusion?

Answer 8

ATP depletion due to reduced O2 supply means Na+ pumps stop working.
Intracellular [Na+] concentration increases.
Reversing mode of function of NCX.
Na+ pumped out but [Ca2+] in cell rises to toxic levels.
Leads to myocardial necrosis, arrhythmia, systolic dysfunction and heart failure.
Reversible upon reperfusion.

Question 9

Name some acid extruders.

Answer 9

NHE - Na/H exchangers

NBC - Na+ dependant Cl-/HCO3- exchanger.

Question 10

Name some transporter that make cell more alkaline.

Answer 10

NBC - Na+ dependant Cl-/HCO3- exchanger.

Na+ HCO3- symporter

Question 11

Name an alkali extruder.

Answer 11

AE - anion exchanger - band - Cl-/HCO3- symporter

Question 12

Describe properties of NHE.

Answer 12

H+ out Na+ in

Electroneutral

Question 13

What is NHE inhibited by?

Answer 13

Amiloride

Question 14

What activates NHE?

Answer 14

Growth factors

Question 15

Describe properties of NBC.

Answer 15

H+ and Cl- out and HCO3- and Na+ in
Electrogenic
Alkalinises cell

Question 16

What is a shared role between all acid and base extruders?

Answer 16

Regulation of cell pH and volume.

Question 17

Alkalisation of cell will lead to increased and decreased activities of what transporters?T

Answer 17

Increased activity of AE.

Decreased activity of NHE and NBC.

Question 18

If a cell begins to swell ions will be extruded.

True or false

Answer 18

True.

Question 19

What are the main ions that begin to get extruded?

Answer 19

Na+ K+ and Cl-.

Question 20

All cells use similar combinations of transporters to achieve regulation of cell volume.

True or false.

Answer 20

False.

There is no standard method for volume regulation.

Question 21

Where is bicarbonate reabsorbed in the kidney?

Answer 21

Proximal tubule.

Question 22

Describe the process of bicarbonate reabsorption.

Answer 22

NaHCO3 - dissociates to Na+ and HCO3-.
Na+ exchanged into epithelium by NHE and H+ into lumen.
H+ bonds to HCO3- - H2CO3 forms.
Carbonic anhydrase action causes dissociation of carbonic acid to H20 and CO2 which will diffuse into the epithelia and recombine under action of carbonic anhydrase to reform H2CO3.
H2CO3 will disassociate in the cell and be exchanged by band 3 (AE) for Cl- into the cell and HCO3- out into blood.
The H+ will be rexchanged for a Na+ by NHE and enter the lumen.
Increased Na+ intracellularly corrected by Na K ATPase - Na out into capillary and K into cell which will leak back out though K channels.
Increased Cl- in cell correct because Cl- leaves though chloride ion channels in the cell back into the blood.

Question 23

What is main reason for retention of bicarbonate in the blood?

Answer 23

Base is being retained for pH buffering capacity.

Question 24

How do ions such as Mg2+ and Ca2+ get reabsorbed in the kidney?

Answer 24

They move through gaps in the epithelium of the nephron.

Mg2+ mainly in the thick ascending limb of the loop of henle.

Ca2+ mainly in the proximal convoluted tubule.

Question 25

Where is Na+ reabsorbed in the kidney?

Answer 25

Mainly in the thick ascending loop of the kidney and the macula densa.

Question 26

Describe the process of Na+ reabsorption in the kidney.

Answer 26

NKCC2 symporter, transports in Na+ along with 2Cl- and K+ into the cell.

From the cell Na+ gets reabsorbed into blood by Na K ATPase.

K+ and Cl - get transported by KClCT into the blood.

Cl- also moves through ClC-Kb into blood.

Some K+ re-enters lumen through ROMK.
Renal outer medullary K+ ion channel.

Question 27

What is furosemide and describe its action?

Answer 27

Is a loop diuretic.

Inhibits NKCC2 Na+ and as a result water is retained in the lumen and therefore more water is lost in urine.