ICPP - ATP Dependent Pumps And Ion Exchangers

Question 1

What are the functions of Na+K+ATPase?

Answer 1

Forms Na+ and K+ gradients (which are necessary for electrical excitability), drives secondary active transport (control of pH, regulation of cell volume and Ca2+ levels, absorption of Na+, nutrient uptake)

Question 2

Should levels of calcium be relatively high or low within the cell?

Answer 2

LOW - high intracellular calcium is toxic to cells.

Question 3

Name the two methods of removing Ca2+ from the cytosol that use primary active transport.

Answer 3

PMCA (expels Ca2+ from cell), SERCA (accumulates Ca2+ into SR/ER)

Question 4

Why do PMCA and SERCA have a high affinity but low capacity for Ca2+?

Answer 4

They remove residual calcium so they do not need to be able to move a large amount.

Question 5

Name the mechanism that removes Ca2+ from the cell via secondary active transport. What is its affinity?

Answer 5

NXC - low affinity but high capacity as it removes most of the calcium from the cell.

Question 6

Name the mechanism which removes Ca2+ from the cell via facilitated diffusion.

Answer 6

Mitochondrial Ca2+ uniports - these only work at high internal calcium levels to attempt to buffer potentially damaging Ca2+.

Question 7

What is ischaemia?

Answer 7

Lack of oxygen due to interruption in blood supply from arteries.

Question 8

What does the NCX do?

Answer 8

It exchanges 3 Na+ for 1 Ca2+, which allows the cell to recover following depolarisation.

Question 9

What is the role played by NCX in cell toxicity following/during ischaemia?

Answer 9

Lack of oxygen means that respiration must be anaerobic, so less ATP is produced. This means that the sodium pump can’t function, and sodium builds up inside the cell. The cell depolarises and NCX reverses, meaning Ca2+ is pumped into the cell. This can be toxic.

Question 10

Name the two acid extruders in the cell.

Answer 10

NHE (exchanges Na+ for H+), NBC (requires Na+ to exchange Cl- and HCO3-)

Question 11

Name the base extruder in the cell.

Answer 11

AE (exchanges Cl- for HCO3-)

Question 12

Which drug inhibits NHE?

Answer 12

Amiloride.

Question 13

This pump moves Na+ and HCO3- into the cell, and H+ and Cl- out of the cell. What is it called?

Answer 13

NBC.

Question 14

What must happen to remedy cell swelling?

Answer 14

Remove Na+, K+, Cl- or organic osmolytes and water will follow them via osmosis

Question 15

What must happen to remedy cell shrinkage?

Answer 15

Influx of Na+, K+, Cl- or organic osmolytes, water will follow by osmosis.

Question 16

Why does drinking alcohol lead to an increase in urination?

Answer 16

Antidiuretic hormone is inhibited, this leads to more water being lost as urine.