M&R Session 2- Ion Trasnporters And Exchangers

Question 0

What four transporters control intracellular calcium levels?

Answer 0

• NCX- imports 3 sodium ions and extrudes 2 calcium ions
• PMCA- extrudes a calcium ion using ATP.
• mitochondrial calcium uniporter- imports calcium into mitochondria when intracellular calcium levels are very high.
• SERCA- imports one calcium into the SR in exchange for one hydrogen ions out.

Question 1

What does the sodium potassium pump do?

Answer 1

It extrudes 3 sodium ions and imports 2 potassium ions.

It uses ATP to do this.

Question 2

Which transporter involved in calcium ion regulation has a low affinity but high capacity?

Answer 2

NCX

Question 3

Which 3 transporters control cellular pH?

Answer 3

• NHE- one sodium ion moves in and one hydrogen ion moves out.
• NBC- one sodium and one HCO3- move in and one H+ and one Cl- move out.
• anion exchanger- HCO3- moves out and Cl- moves in.

Question 4

How does a sodium, glucose co-transporter work?

Answer 4

It is a symporter. The energy generated when sodium moves in allows glucose to be moved in against the concentration gradient.

Question 5

How is cell swelling resisted?

Answer 5

Efflux of ions

Question 6

How is cell shrinkage resisted?

Answer 6

Influx of ions

Question 7

Why is the ability of the NCX to reverse important in ischaemia?

Answer 7

In Ischaemia, ATP is depleted, therefore the sodium/potassium pump can no longer function and sodium builds up intracellularly.
This causes the cell to depolarise, and the NCX to therefore be reversed.
This means that calcium now moves into the cell, whilst sodium is pumped out; causing high levels of intracellular calcium, which can be toxic!