Lecture 2: ATP Dependant Ion Pumps And Ion Exchangers

Question 1

What is the role of NA+/K+ ATPase ?

Answer 1

• pumps 3NA+ out of the cell and 2K+ into the cell.
• it forms the NA+ and K+ gradients
• it contributes to 5mV to resting membrane potential.
• it drives secondary active transport.

Question 2

What is the concentration of calcium in the cell and outside the cell ? And is the concentration of calcium greater outside or inside the cell ?

Answer 2

• concentration of calcium is greater outside the cell than inside.

Intracellular concentration : 50-100nm

Extracellular concentration : 2mM.

Question 3

Why is the concentration of calcium inside the cell very low compared to the outside ?

Answer 3

• because high concentrations of calcium are toxic and needs to be controlled.

Question 4

How is the resting concentration of Ca2+ controlled ?

Answer 4

It first begins with primary active transport :

1) plasma membrane Ca2+ -ATPase removes residual Ca2+ from the cell into the outside of the cell.
2) sarcoplasmic recticulum Ca2+ ATPase removes residual Ca2+ from the cell into themselves.

SECONDARY ACTIVE TRANSPORT THEN OCCURS :

3) Na+ -calcium exchanger : exchanges 3NA+ for 1Ca2+ out of the cell.
4) Ca2+ uniporters in mitchochondria take in ca2+.

Question 5

does the plasma membrane ca2+ ATPase and sarcoplasmic reticulum ca2+ ATPase have high affinity or low affinity ? and does it have a low capacity or high capacity ?

Answer 5

• the plasma membrane Ca2+ ATPase and sarcoplasmic reticulum Ca2+ ATPase both have high affinity but very low capacity.

Question 6

What does electro genie mean ? In relation to the sodium - calcium exchanger

Answer 6

• current flows in the direction of the Na+ gradient

Question 7

In a sodium calcium exchanger , how many sodium are transported into the cell and how many calcium are transported out of the cells?

Answer 7

• 3 Na+ ions for 1 calcium ion.

Question 8

Does t current flow in direction with this sodium or calcium electrochemical gradient in a sodium calcium exchanger ?

Answer 8

• sodium.

Question 9

What occurs to the flow of Na and ca when a cell in polarised - in a calcium -sodium exchanger?

Answer 9

Normal flow of sodium-calcium exchanger will happen. 3NA+ move into the cell whereas 1 calcium is moved out of the cell.

Question 10

What two ion channels help to regulate pH acidity ?

Answer 10

ACID EXTRUDERS :

• Na/H+ exchanger which removes 1 h+ in exchange for 1Na+.
• Na+ dependant Cl-/HCO3- exchanger. This transports bicarbonate and sodium into the cell ; and h+ and cl- out of the cell.

Question 11

Which ion channels help to regulate pH - prevent cell becoming to alkaline

Answer 11

BASE EXTRUDERS

1) cl-/HCO3- exchanger : HCO3- leaves for every cl- that enters

Question 12

How does Na+/K+ ATPase ALSO help regulate cellular pH?

Answer 12

• primary pump : The sodium that leaves the cell via the sodium - K ATPase can be used as input for the sodium /H exchanger , the Na+ dependant Cl-/HCO3- exchanger.

Question 13

What is the role of Amiloride with the Na+/H+ exchanger ?

Answer 13

• Amiloride inhibits the Na+/H+ exchanger.

Question 14

How is cell volume regulated in order to prevent cell swelling ?

Answer 14

• extrude ions out the cel eg K+, cl when the cell is swelling because this would allow water to also leave.
• when the cell is shrinking , we want water to enter the cell so we want an influx of ions.
• cl-/ HCO3- exchanger : HCO3- enters the cells , whereas cl- leaves the cells , this results in HCO3- combining with H+ which creates H2CO3 - released as CO2.

Question 15

Why does the kidney reabsorb all the bicarbonate ?

Answer 15

• because it needs to retain base for pH buffers.

Question 16

What are loop diuretics and what can they be used to treat ?

Answer 16

• loop diuretics are used to treat those with hypertension
  Or oedema as they increase loss of water via urine. They do this by blocking the Na+/K+/2cl- symporter in the ascending limb which restrict Na+ absorption.

Question 17

What are thiazides and what can they be used to treat ?

Answer 17

Thiazides block the real of Na+ by inhibiting the Na/cl - cl transporter ,
In the distal convoluted tubule which results in fluid loss.

• can be used to treat high blood pressure as it reduces volume of plasma.

Question 18

What is the role of ADH ?

Answer 18

• acts on the aquaporins on the collecting duct , they increase permeability to water and allow more water to be reabsorbed back into the blood.

Question 19

What are the effects of alcohol on ADH secretion ?

Answer 19

• suppresses ADH secretion , which results in less water being reabsorbed back into the blood and more being released via urine.

Question 20

What is the role of aldosterone ?

Answer 20

• it binds to mineralcorticoid receptors on the collecting duct , which stimulates the synthesis of ROMK , Na+/K+ ATPase and epithelium sodium channel complex.This causes more Na+ to be reabsorbed back into the blood. This causes greater water retention = high blood pressure.

Question 21

What is the role of Amiloride and spiromolactone ?

Answer 21

• they antagonise the effects of aldosterone. Preventing Na+ reabsorption into the blood , thus water remains in the collecting duct. Thus , lowering water retention.

Question 22

Give an example of anion exchangers

Answer 22

Cl-/HCO3- exchanger which acidifies a cell.

Question 23

What occurs to the Na+ / Ca2+ exchanger during a depolarised state of cells ?

Answer 23

The mode of operation of NCX is inhibited and its mode of operation reverses ie to bring Ca2+ into the cell and Na+ out of the cell. In this way , NCX makes a contribution to Ca2+ influx during cardiac action potentials and thus CAN potentially contribute to Ca2+ toxicity during periods of ischaemia.