Lecture 2: ATP Dependant Ion Pumps And Ion Exchangers Flashcards
What is the role of NA+/K+ ATPase ?
- 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.
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 ?
- concentration of calcium is greater outside the cell than inside.
Intracellular concentration : 50-100nm
Extracellular concentration : 2mM.
Why is the concentration of calcium inside the cell very low compared to the outside ?
- because high concentrations of calcium are toxic and needs to be controlled.
How is the resting concentration of Ca2+ controlled ?
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+.
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 ?
- the plasma membrane Ca2+ ATPase and sarcoplasmic reticulum Ca2+ ATPase both have high affinity but very low capacity.
What does electro genie mean ? In relation to the sodium - calcium exchanger
- current flows in the direction of the Na+ gradient
In a sodium calcium exchanger , how many sodium are transported into the cell and how many calcium are transported out of the cells?
- 3 Na+ ions for 1 calcium ion.
Does t current flow in direction with this sodium or calcium electrochemical gradient in a sodium calcium exchanger ?
- sodium.
What occurs to the flow of Na and ca when a cell in polarised - in a calcium -sodium exchanger?
Normal flow of sodium-calcium exchanger will happen. 3NA+ move into the cell whereas 1 calcium is moved out of the cell.
What two ion channels help to regulate pH acidity ?
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.
Which ion channels help to regulate pH - prevent cell becoming to alkaline
BASE EXTRUDERS
1) cl-/HCO3- exchanger : HCO3- leaves for every cl- that enters
How does Na+/K+ ATPase ALSO help regulate cellular pH?
- 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.
What is the role of Amiloride with the Na+/H+ exchanger ?
- Amiloride inhibits the Na+/H+ exchanger.
How is cell volume regulated in order to prevent cell swelling ?
- 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.
Why does the kidney reabsorb all the bicarbonate ?
- because it needs to retain base for pH buffers.
What are loop diuretics and what can they be used to treat ?
- 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.
What are thiazides and what can they be used to treat ?
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.
What is the role of ADH ?
- acts on the aquaporins on the collecting duct , they increase permeability to water and allow more water to be reabsorbed back into the blood.
What are the effects of alcohol on ADH secretion ?
- suppresses ADH secretion , which results in less water being reabsorbed back into the blood and more being released via urine.
What is the role of aldosterone ?
- 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.
What is the role of Amiloride and spiromolactone ?
- they antagonise the effects of aldosterone. Preventing Na+ reabsorption into the blood , thus water remains in the collecting duct. Thus , lowering water retention.
Give an example of anion exchangers
Cl-/HCO3- exchanger which acidifies a cell.
What occurs to the Na+ / Ca2+ exchanger during a depolarised state of cells ?
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.