3.2 ATP-dependent Pumps And Ion Exchangers

Question 1

Na pump
How does it work?
What is its function?

Answer 1

1. Na,K Pump
   3Na+ out, 2K+ in, ATP (primary AT), Antiport
2. Forms Na+ and K+ gradients
   Necessary for electrical excitability
   Drives secondary active transport (Na+H+ exchanger) (Na+Glucose Cotransport)

Question 2

Na+H+ exchanger
How does it work
What is it driven by
What is its function?

Answer 2

1. 1Na+ in, 1 H+ out, secondary AT, antiport
2. Driven by Na pump forming ionic concentration gradient on either side of cell
3. Control of pH (Acid extruder), regulation of cell volume, absorption of Na+ in epithelial

Question 3

Na+glucose cotransporter
How does it work
What is it driven by
What is its function?

Answer 3

1. 2Na+ in, 1 glucose in against conc gradient, secondary AT, symport
2. Driven by Na pump forming ionic concentration gradient on either side of cell
3. Nutrient uptake e.g. Glucose, amino acids in small intestine

Question 4

Changes of calcium intracellularly cause cell signalling cascades. Is the change of calcium quite big or small?

Answer 4

Tiny!

Question 5

How is calcium controlled intracellularly (Removed)?

Answer 5

PMCA - on cell membrane, ATP dep (primary AT), 1 Ca2+ out
SERCA - on ER/SR membrane, ATP dep (primary AT), 1 Ca2+ into ER/SR
NCX - Na+Ca2+ exchanger, 3Na+ in, 1Ca2+ out
Mitochondrial Ca2+ uniport - operate at high [Ca2+] to buffer

Question 6

Main protein removing calcium? Side man proteins?

Answer 6

NCX removes most, SERCA and PMCA removes residual

Question 7

When does the mitochondria help with the control of resting calcium levels in the cell? What happens if it cant and levels get too high?

Answer 7

Operate at high Ca2+ levels
Usually when other transport proteins arent working
When calcium gets too high though and cant be controlled, mitochondria recognises and starts apoptosis

Question 8

How does Sodium Calcium Exchanger work? Function?

Answer 8

1. 3Na+ in, 1 Ca2+ out
2. Electrogenic - current flows in the direction of the Na+ gradient
3. Driven by ionic concentration gradient (Na+ extracellular) so secondary AT
4. Antiport
5. Function is during cell recovery it expels Ca2+

Question 9

NCX membrane potential dependent. Movement of molecules if cell polarised and then cell depolarised?

Answer 9

1. Polarised when high Ca2+ in, Na+ out, causing Ca2+ push out and Na+ in
2. Depolarised when high Na+ in, Ca2+ out, causing Na+ out and Ca2+ in

Question 10

Activity of NCX in ischaemia?

Answer 10

1. Sodium potassium pump not working as no ATP - Na+ accumulates inside cell, cell depolarised
2. This causes NCX to pump sodium out now and calcium in (opp. To what it does when controlling resting calcium), but too much calcium inside cells is toxic!
3. Can cause MI

Question 11

Two types of transport proteins controlling cell pH

Answer 11

1. Acid extruder - Na+/H+ extruder, sodium bicarbonate cotransporter (Na+ dependent Cl-/HCO3- exchanger)
2. Base extruder - anion exchanger (Cl-/HCO3- exchanger)

Question 12

How do NBC and AE work?

Answer 12

1. Sodium Bicarbonate Cotransporter - Acid Extruder
   - H+ out, Na+ in. Cl- out, HCO3- in.
   - secondary AT (Na pump helps)
2. Anion Exchanger - Base Extruder
   - HCO3- out, Cl- in

Question 13

NHE, NBC and AE all related to acid and base extrusion. What else are they related to?

Answer 13

Regulating cell volume

Question 14

Normal range of pH intracellularly?

Answer 14

7.2-7.5

Question 15

If cell swells, where do ions move?

If cell shrinks, where do ions move?

Answer 15

• extrude ions

- influx of ions

Question 16

How many water molecules move if 1 sodium, potassium or chlorine moves in/out of cell?

Answer 16

6 molecules

Question 17

Give a mechanism that resists swelling

Answer 17

Conductive system
K+ out
Cl- out
H2O out

Question 18

Give a mechanism that resists shrinking.

Answer 18

Cotransport systems
E.g. Na+Glucose Cotransport/Na+organicosmolytes
Na+ and glucose in
H2O in