Session 2.2 - ATP - Dependent Ion Pumps and Ion exchangers Flashcards
Give the free ion distribution of Na+, K+, Ca2+ and Cl- inside the cell
Na+ - 10mM
K+ - 160mM
Ca2+ - 1 x 10^-4mM
Cl- - 3 mM
Give the free ion distribution of Na+, K+, Ca2+ and Cl- outside of the cell
Na+ - 145 mM
K+ - 4.5mM
Ca2+ - 1.5mM
Cl- - 114 mM
Describe the process of the Na+/K+-ATPase pump
- Exchanges 3 intracellular Na+ for extracellular 2K+
- Creates high intracellular K+
- Antiport protein
What does the Na+/K+-ATPase pump drive?
Processes of secondary active transport via formation of Na+ concentration gradient
Why must levels of Ca2+ in cells be controlled?
High Ca2+ toxic to cells
What is SERCA? Describe its process (4)
- Antiport protein
- High affinity low capacity for Ca2+
- Accumulates Ca2+ into the Sarcoplasmic reticulum/Endoplasmic Reticulum in exchange for H+
- Primary active transport: ATP hydrolysis
What is PMCA?
- Antiport protein
- High affinity, low capacity for Ca2+
- Intracellular Ca2+ exchanged for extracellular H+ (expels Ca2+)
- Primary active transport: ATP hydrolysis
What type of active transport is demonstrated by NCX?
What is its normal role?
- Secondary active transport
* Expelling Ca2+ during cell recovery
What is the process of transport for NCX?
- 3 Na+ into cell, 1 Ca2+ out of cell
* Electrogenic - current flows in direction of Na+ gradient
What is NCX dependent on?
Membrane potential
What happens to NCX in depolarised cells?
The normal mode of operation is inhibited and reversed, so Ca2+ enters cell.
What role does NCX have in ischaemia?
- ATP depleted due to lack of O2
- Sodium pump inhibited – no movement of Na+ out of cell
- NCX reverses, as outside negative: Ca2+ in, 3 Na+ out
- High Ca2+ toxic to cell – activates potent enzymes
What is the process of NHE cotransporter?
- Na+ in, H+ out
* Gradient follows Na+ - no ATP hydrolysis
What does the NHE contransporter regulate?
o Cell volume i.e. cell swelling: increase ion efflux – water follows by osmosis, cell shrinkage: increase ion uptake
o pH
What is the NHE cotransporter activated and inhibited by?
- Activated by growth factors/ inhibited by amiloride
What is NBC?
- Na+ and HCO3- into cell, Cl- out
* Gradient follows Na+
What occurs in cell when buffering exceeded?
Control of cellular pH is given to variety of plasma membrane transporters
What is acidification of a cell opposed by?
- Expelling H+ via the Na+/H+ exchanger (NHC) or the inward movement of bicarbonate via NBC.
What is alkalisation of a cell opposed by?
- Expelling bicarbonate via the anion exchanger
* HCO3- out, Cl- in
What is AE?
Anion exchange
HCO3- out, Cl- in.
Why are electroneutral transport ions used to mediate osmotic strength of cytoplasm?
Allows osmotic strength to be varied without effect on membrane potential
What do cells do in response to swelling? What happens in shrinkage?
Extrude ions (Na+, K+, Cl-) Influx ions (Na+, K+, Cl-) Water follows ions down osmotic gradients
Give three ways cell swelling can be resisted
Conductive transporters
Contransport systems
Solute molecules exprelled
Why is all bicarbonate filtered into proximal tubule of the kidney reabsorbed?
Retains base for pH buffers
