Ion transport in cellular physiology Flashcards
functions of sodium pump
forms Na+ and K+ gradient which is neccesray for electrical excitability
drives secondary active transport- control of pH, regulation of cell vol an intracellular ca2+, absorption of Na+ in epithelia, nutrient uptake (glucose from intestine)
control of resting [Ca2+]i
primary active transport:plasma membrane Ca2+-ATPase(PMCA) expels Ca2+ out of the cell, Sarco(endo)plain reticulum Ca2+-ATPase(SERCA) accumulates Ca2+ into the SR/ER. both have high affinity and low capacity
secondary transport :Na+-Ca+-exchange(NCX), removes calcium , high capacity low affinity
facilitated transport: mitochondrial Ca2+ uniports (offer at high [Ca2+]I to buffer potentially damaging Ca2+
functions of NCX
exchanges 3Na+ for 1Ca2+
role in expelling intracellular Ca2+
possible role in cell toxicity during ischaemia/reperfusion
electrogenic-depolarises a normally polarised membrane. current flows in the direction of the Na+ gradient
NCX in ischaemia
low o2 so oxidative phosphorylation nt running properly so insufficient ATP and sodium pump is inhibited
[Na+]in accumulates and cell is depolarised
NCX reverses and Na+ is now going out but there is high Ca2+ toxicity
how is cell pH controlled by transporters
efflux of H+ via NHE
Na+ dependent Cl-/HCO3-exchanger
Cl-/HCO3- exchanger
function of NHE
exchanges extracellular Na+ for intracellular H+
regulates intracellular pH
regulates cell vol
activated by growth factors
what is NHE inhibited by
amiloride
how is cell vol regulated
transport of osmotically active ions e.g Na+, K+, Cl- or organic osmolytes (amino acids)
water follows
cell swelling-extrude ions
cell shrinking-influx ions
how can [Ca]I be raised
facilitated diffusion by: receptor-operated Ca2+ channels, voltage operated Ca2+ channels, IP3 gated CA2+ channel
secondary active transport- Na+-Ca+ exchange (NCX) in reverse mode in depolarised cells
