ATP-dependan Pumps And Ion Exchange Flashcards
What is the function of the Na pump?
Na+_K+_ATPase
Forms Na+ and K+ gradients - needed for electrical excitability, (only -5mV to rest potential)
Drives secondary active transport - control pH, regulate cell volume, and conc Ca2+, absorb Na+ in epithelia, nutrient uptakes
Why is the control of calcium so important?
Intracellular Ca is very low compared to outside maintaining a large gradient.
High intracellular calcium is toxic to cells (as it joins with phosphate and becomes insoluble and forms deposits)
Cells signal by very small changes in intracellular pH so level must be maintained or false signals are sent.
How is intracellular Ca conc maintained?
Primary active transport= PMCA expels Ca out of cell (high affinity, low capacity so removes residual ca) and SERCA (high affinity, low capacity so removes residual Ca into the SER)
Secondary active transport= NCX (low affinity, high capacity swaps residual Ca for Na using Na conc grad)
Facilitated transport= Mitochondrial Ca Uniports (operate at very high Ca to buffer any potential damage)
Describe NCX- the sodium calcium exchanger
Exchanges 3Na+ for 1 Ca2+
Secondary active transport (uses Na conc)
Electrogenic- current flows in direction of Na grad but not probable as cell -ve.
Role in expelling intracellular Ca2+ during cell recovery
Possible role in cell toxicity during ischemia/reperfusion
What is unusual about the NCX’s relationship with the membrane potential.
It’s membrane potential dependant.
When the cell is polarise (-ve inside) it moves Ca2+ out and 3Na+ into the cell
When the cell is depolarised (-ve outside) it lets 3Na+ out and Ca2+ in.
So the depolarised membrane potential reverses the mode of operation (allows Ca2+ influx in cardiac action potential)
What happens to the NCX in Ishcemia?
Ischemia=low ATP and low O2
The Na+_K+_ATPase is inhibited so Na+ accumulates in the cell depolarising it.
This reverses the action of the NCX to remove the Na+ and bring Ca2+ in. However the conc of intrecalleular Ca2+ rises and this can b toxic.
How do transporters contributes to cellular pH?
Acid extrudes remove H+ ions and/or bring base into the cell
Base extrudes remove base from the cell.
List some acid extrudes and the molecules they move.
Na+/H+ exchanger (NHE) removes H+ from cell
Na+ dependant Cl-/HCO3- exchanger (acid out and base in) NBC sodium bicarbonate transporter. This moves H+ out and HCO3- in along with other ion movement.
List some base extrudes and the molecules they move.
CL-/HCO3- exchanger (AE) (anion exchanger) moves base HCO3- out of cell
Key points f the NHE (Na+/H+ exchanger)
Exchanges extracellular Na+ for intracellular H+
Electro neutral change
Regulate pH
Regulate cell volume (H2O follows Na+)
Activated by growth factors (excess H+ caused by growth_
Inhibited by Amiloride
Key info about the 2 bicarbonate transporters
NBC and AE
NBC= alkalinises cell (acid out + base in) (H+ and HCO3-)
AE= acidified cell (base out) (HCO3-)
Both involved in cell volume regulation as osmotically active ion moment occurs
How do transporters co-ordinate intracellular pH regulation?
PH is held at set point where lines on graph cross. Any drift from this point is corrected by increased activity of either acidic or basic transporters.
How is cell volume regulates?
The transport of osmotically active ions (Na+, K+, Cl-, or organic osmolytes-AA’s)
Water follows them
Is cell is swelling-extrude ions to remove H20
If cell is shrinking-influx ions to gain H20
What is the key point of volume regulation?
No standard method, diff cell types have diff combinations of transporters to achieve the regulation they need.
They should be electro-neutral to avoid unwanted potentials being created .
