ATP-dependent Pumps and Ion Exchangers

Question 1

What is an Na+ dependent Cl-/HCO3- exchanger (NBC)?

Answer 1

1Na in for 1H+ out, 1HCO3 in for 1Cl- out

Co-transporter, Alkalinises cell = control cell pH/vol

Question 2

Give an example of an anion exchanger

Answer 2

Cl-/HCO3- exchanger, base extruder = control cell pH/vol

Question 3

Describe sodium hydrogen exchanger Na+/H+ (NHE)

Answer 3

Acid extruder = control cell pH

Electroneutral 1 Na= in : 1 H+ out exchanger

Regulates cell vol – when proton moves so does water

Inhibited by amiloride

Question 4

When is a mitochondrial Ca2+ Uniport used?

Answer 4

If Ca gets too high, uses mitochondria uniporter as buffer in attempt to save cell

Question 5

Describe a sodium calcium exchanger Na+ Ca+ (NCX)

Answer 5

3 Na+ inside for 1 Ca2+ outside

Secondary active transport, exchanger is reversible

Role in expelling Ca2+ in cell recovery, Membrane potential dependent –> polarised = Ca out, depolarised = Ca in

Ischemia = no ATP = Na pump inhibited = high Na = cell depolarises = Ca in = toxic

Question 6

Which exchanger is not a pump and why?

Answer 6

Sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA)

NOT A PUMP NOT ATTACHED TO PLASMA MEMBRANE

1ATP for 1Ca2+ inside SR/ER, Primary activity transport

Question 7

What is the Plasma membrane Ca2+ ATPase (PMCA)?

Answer 7

1 ATP for 1 Ca2+ outside the cell, Ca toxic to cells – lots of phosphate from ATP hydrolyses inside cells = crystallise, Primary activity transport

Question 8

Describe the Sodium-potassium ATPase (Na+-K+-ATPase, ‘The Na pump’)

Answer 8

moves 3 Na out, 2 K in to maintain normal conc gradient, controls pH, cell vol and [Ca2+], provides energy for glucose uptake

high internal K = resting membrane potential (-70mV),

antiport, co-transport

creates Na+ gradient to provide energy for transporters

Question 9

What happens to the Na Ca2+ exchanger in ischaemia?

Answer 9

The NCX reverses, originally Ca 2+ out and 3Na+ in

No O2 = no ATP = Na K ATPase depleted = high [Na+] = cell depolarisation = now Ca2+ in = high [Ca2+] = toxic

Question 10

What is the [Ca2+] inside and outside the cell?

Answer 10

Inside = ~0.0001mM Outside = ~1mM

Question 11

Why is there such a different in [Ca2+] outside to inside the cell?

Answer 11

Ca2+ is toxic = cell death.

Low [Ca2+] allows small conc changes to cause a large response. ~10,000 - 20,000 fold diff

Question 12

How do you work out folds?

Answer 12

(B-A)/A

(4-2) = 2/2 = 1 –> 1 fold diff between 2 and 4

Question 13

How would you write 3x10^-6 in full?

Answer 13

0.000003

Question 14

How is Intracellular [Ca2+] lowered?

Answer 14

PMCA - plasma membrane Ca2+ ATPase
NCX - Na+ Ca2+ exchanger
SERCA - Sarco(endo)plastic reticular Ca2+ ATPase
Mitochondrial Ca2+ uniporter

Question 15

How is Intracellular [Ca2+] raised?

Answer 15

VOCC - voltage operated calcium channel
SOC - store operated channel
LGIC - ligand gated ion channel
RyR - ryanodine receptor: release Ca2+ from SER
GCPR IP3 - release Ca2+ from SER

Question 16

How does the SERCA - Sarco(endo)plastic reticular Ca2+ ATPase pump work?

Answer 16

uses ATP, 1H+ out for 1Ca2+ in

used when storage is low or residual [Ca2+] high

Question 17

In general terms how does cell volume regulation occur

Answer 17

cell swelling = extrude ions
cell shrinking = influx ions

every ion moves 6 H2O

Question 18

Why can Cl-, Na+, K+, Ca2+ be classed as osmolytes?

Answer 18

every ion moves 6 H2O

Question 19

What are diuretic drugs used for?

Answer 19

block transporters that reabsorb Na+, more lost in urine, more water therefore also lost = helps treat oedema

Question 20

Why is all the bicarbonate absorbed in the kidneys?

Answer 20

to retain the base when controlling cell pH levels

Question 21

Why is all the Na reabsorbed in the kidneys?

Answer 21

Na K ATPase creates low intracellular [Na+] = Na+ moves back into cells down conc gradient = all absorbed