Lecture 5: Transporters, Ion Channels And Pores Part 2

Question 1

What are the major physiological roles of the sodium-potassium ATPase (Na pump)?

Answer 1

• Uses ATP to drive 3Na+ out and bring 2K+ in
• Forms Na+ and K+ gradients to provide energy for other transporters
• Drives secondary active transport

Question 2

What are the major physiological roles of the plasma membrane Ca2+ ATPase (Ca2+ Mg2+ ATPase)?

Answer 2

• Uses ATP to drive Ca2+ out and bring H+ in

Question 3

What are the major physiological roles of the sarcoendoplasmic reticulumATPase (SERCA)?

Answer 3

Uses ATP to drive Ca2+ in and H+ out of cell storage

Question 4

What are the major physiological roles of sodium calcium exchanger (NCX)?

Answer 4

• Activity depends on membrane potential
• Exchanges 3 Na+ for 1 Ca2+
• If cell is polarized (more negative inside than outside), brings nett ossified charge in
• If cell is depolarized (becoming less negative inside), brings nett positive charge out
• Has a role in expelling intracellular Ca2+ during cell recovery

Question 5

What are the major physiological roles of the sodium hydrogen exchanger (NHE)?

Answer 5

• Exchanges extracellular Na+ for intracellular H+
• Regulates pH in the cell and cell volume
• Activated by growth factors and inhibited by amiloride

Question 6

What are the major physiological roles of anion exchange?

Answer 6

• Brings in Cl- and removes HCO3-
• Exchanges one anion for another
• Regulates pH - acidifies cell

Question 7

How does ion transport contribute to cellular Ca2+ handling?

Answer 7

• PMCA removes residual Ca2+ via primary active transport
• SERCA accumulates Ca2+ into ER via primary active transport
• Na+ Ca+ exchange (NCX) removes most Ca2+ via secondary active transport
• Mitochondrial Ca2+ uniports operate at high [Ca2+] to buffer potentially damaging Ca2+ via facilitated transport

Question 8

How does ion transport contribute to cellular pH regulation?

Answer 8

• Acidification activates NHE (sodium hydrogen exchanger to remove H+) and NBC (sodium dependent chloride bicarbonate cotransporter to remove H+ and bring in HCO3-)
• Alkalinisation activates AE (anion exchangers removes HCO3-)

Question 9

How does ion transport contribute to cell volume regulation?

Answer 9

• By regulating transport of osmotically active ions (Na+ etc)
• Water follows
• Cell swelling - extrude ions to extrude water
• Cell shrinking - influx ions to influx water