M&R 2.2 - ATP Dependent Pumps And Ion Exchangers

Question 1

What are the functions of the sodium ion pump?

Answer 1

• Form Na+K+ gradient (used in membrane potentials)

- Promotes secondary active transport (pH control, cell volume and Ca2+ regulation, Na+ absorption and nutrient uptake)

Question 2

What is the Na+Ca2+ exchanger otherwise known as?

Answer 2

NCX

Question 3

What is the ratio of ion transport of NCX? What happens as a result of this?

Answer 3

• 3 Na+ into cell : 1 Ca2+ out of cell

- Membrane becomes electrogenic so the current runs in the direction of the Na+ gradient

Question 4

What is the function of NCX?

Answer 4

Expels intracellular Ca2+ during cell recovery from signalling

Question 5

What happens when NCX becomes depolarised?

Answer 5

• Works in reverse (3Na+ out, 1Ca2+ in)

- Lead to a high concentration of extracellular Na+ and high concentration of intracellular Ca2+

Question 6

What happens to NCX during ischaemia/ after reperfusion?

Answer 6

The depletion of ATP causes it to become partially depolarised which can produce toxicity

Question 7

What is the Na+H+Exchanger otherwise known as?

Answer 7

NHE

Question 8

What is the ratio of ion exchange of NHE?

Answer 8

• 1 Na+ in: 1 H+ out so is electroneutral

Question 9

What are the functions of NHE? What is it activated by?

Answer 9

• pH regulation (is an acid extruder)
• Cell volume regulation
• Drug target for Amiloride
• Activated by growth factors

Question 10

Name the two bicarbonate transporters and give their shorthand terms

Answer 10

• Na+bicarbonate-chloride cotransporter (NBC)

- Anion exchanger (AE)

Question 11

What is the function of NBC and how is this achieved?

Answer 11

• Alkalinises cell

- 1 Na+ and 1 HCO3- in : 1 H+ and 1 Cl- out

Question 12

What is the function of AE and how is this achieved?

Answer 12

• Acidifies cell

- 1 HCO3- out : 1 Cl- in

Question 13

What the full name of PMCA?

Answer 13

Plasma membrane Ca2+ ATPase

Question 14

What are the functions of PMCA?

Answer 14

• Removes 1 Ca2+ from cell and brings 1 H+ in

- Removes residual Ca2+ by having a high affinity but a low capacity

Question 15

What is the full name of SERCA?

Answer 15

Sarco(endo)plasmic reticulum Ca2+ ATPase

Question 16

What are the functions of SERCA?

Answer 16

• Removes 1 H+ and brings 1 Ca2+ in

- Accumulates Ca2+ in sarcoplasmic/endoplasmic reticulum by having a high affinity but a low capacity

Question 17

What kind of active transporter are SERCA and PMCA?

Answer 17

• Primary active transporter

- Use ATP

Question 18

What are the intracellular and extracellular concentrations of Ca2+?

Answer 18

• Intracellular = 50-100nM

- Extracellular = 2mM

Question 19

Which three transport methods contribute to the transport of calcium ions? Why does there need to be so many?

Answer 19

• Primary active transport e.g. SERCA
• Secondary active transport e.g. NCX
• Facilitated transport e.g. VOCC
• If only one was used, the appropriate concentrations wouldn’t be able to be reached

Question 20

Which transporters contribute to the control of cellular calcium levels?

Answer 20

• PMCA
• SERCA
• NCX
• Mitochondria Ca2+ uniports

Question 21

What is the function of the mitochondrial Ca2+ uniports?

Answer 21

• Buffer away from cytoplasm when concentrations of Ca2+ are high
• Move H+ into inter membrane space which causes an electrical gradient

Question 22

Which transporters are acid extruders?

Answer 22

• NHE - removes H+ so is protective in highly metabolising tissues
• NBC

Question 23

Which transporters are base extruders?

Answer 23

AE - chloride is also brought in therefore acidifying

Question 24

How is cell volume regulated? In what environment can this be achieved?

Answer 24

• Transport of osmotically active ions e.g. Na+ to which water follows
• Has to be done in an ELECTRONEUTRAL environment

Question 25

What causes swelling and shrinkage of the cell?

Answer 25

• Swelling = INFLUX of ions therefore more water inside

- Shrinkage = EXTRUSION of ions therefore more water outside

Question 26

Where does renal bicarbonate absorption happen? What is the aim of this?

Answer 26

• Proximal tubule of the kidney

Goals are:

• H2CO3 retention for pH buffers
• pH and cell volume regulation

Question 27

How is Na+ retained in the proximal tubule?

Answer 27

• NHE transports Na+ into cell from lumen of proximal tubule
• Na+ pump transfers Na+ into the capillary from the cell

Question 28

How is H2CO3 retained in the proximal tubule?

Answer 28

• NHE exchanges H+ for Na+
• H+ combines with HCO3- to make H2CO3
• H2CO3 is broken down by carbonic anhydrase to form H2O and CO2
• Diffuse readily across membrane and recombine in cell
• H2CO3 transported into capillary by AE

Question 29

Which transporter is targeted in the thick ascending limb of the kidney during diuretic treatment? What is the effect of this?

Answer 29

• NKCC2 (Na+K+Cl- move in)
• Is inhibited when loop diuretics bind
• Limits reuptake of Na+ therefore less water reabsorbed
• Blood volume is decreased
• Decreases blood pressure

Question 30

Which transporters are targeted in the distal convoluted tubule of the kidney during diuretic treatment? What is the effect of this?

Answer 30

• Thiazide inhibits Na+Cl- cotransporter and does the same as loop diuretics
• Amiloride inhibits Epithelial Na+ Channel and does the same as loop diuretics

Question 31

Which transporters are targeted in the cortical collecting duct of the kidney during diuretic treatment? What is the effect of this?

Answer 31

• ENaC
• Na Pump
• ROMK
• Spironolactone inhibits therefore inhibiting aldosterone

Question 32

What is the function of aquaporin? What stimulates this?

Answer 32

• A water channel, ensures efficient water uptake along with Na+
• Stimulated by ADH

Question 33

What is Na+K+ATPase otherwise known as?

Answer 33

Sodium pump