Session 3.2: Ion Transport in Cellular Physiology Flashcards
what is the function of Na/K/ATPase pump
- forms Na and K gradients, necessary for electrical excitability
- drives secondary active transport, for control of pH, regulation of cell volume and concentration of calcium ions, absorptuon of Na in epithelia, nutrient uptake like glucose from small intestine
what are the intracellular calcium concentrations at rest
50-100nM
what are the extracellular calcium concentrations at rest
2mM
why does the cell need to remove calcium
if high - toxic
small rises in calcium
excitability
what are the mechanisms of controlling calcium concentration at rest
primary active transport -
PMCA: Ca out (high affinity)
SERCA: Ca acculumates into SR/ER (high affinity)
secondary active transport -
Na-Ca exchange (low affinity)
facilitated transport:
mitochondria Ca uniports (operate at high Ca to buffer)
how does the sodium calcium exchanger affect cell physiology
exchanges 3Na for 1Ca
role in expelling intracellular Ca during cell recovery
possible role in cell in toxicity during ischaemia/reperfusion
ELECTROGENIC - current moves in the direction of the Na gradient
how is the sodium calcium exchanger activity membrane potential dependent\
if cell polarised, high calcium in and low sodium in
if cell depolarised, high sodium in and low calcium in
so the depolarised membrane reverses mode of operation. so if depolarised = calcium influx
how does the sodium calcium exchanger result in ischaemia
low O2 - ATP not formed from oxidative phosphorylation - sodium pump inhibited - sodium accumulates - cell depolarises - switches mode - sodium goes outside cell - calcium inside cell - high calcium toxicity
how do ion transporters control cell pH
Na/H exchanger = acid extruder
Na dependent Cl/HCO3- exchanger = acid extruder so alkalinisation
Cl-/HCO3- exchanger = base extruder so acidification
what are the key features of the Na/H exchanger
sodium in, H out regulates pH regulates cell volume activated by growth factors inhibited by amiloride
what is special about a bicarbonate transporters
got both Na-bicarbonate-chloride cotransporter and anion exchanger:
can either alkaline a cell or acidify a cell
both involved in volume regulation
at what pH does sodium/hydrogen exchange best work at
low activity at high pH where concentration of hydrogen ions is low
activated by acidification
at what pH does Cl/HCO3 (anion) exchange best work at
activated by alkalination
at what pH does sodium dependent Cl/HCO3 exchange best work at
activated by acicification
how is cell volume regulated
transport of osmotically active ions - sodium, potassium, chloride or amino acids
then water follows, cell swelling, then to get rid of water = extrude ions and water and vice versa if cell shrinking
what mechanisms are there to resist cell swelling
Conductive systems: potassium efflux(change membrane potential) + chloride efflux
cotransport systems: potassium and chloride out and so does water
potassium out, Hydrogen in, acidify cells, buffered by hydrogen carbonate ions which together form carbonic acid and diffuses out as CO2. As HCO3 comes in, Cl out in order to control pH, so water follows
what mechanisms are there to resist cell shrinking
Conductive systems: sodium and calcium into cell, water follows
Contrasnport systems: sodium, chloride in or
sodium/amino acid in or sodium/potassium/chloride in
or sodium in, hydrogen out, alkalinising cell. hydrogen ions are provided by the breakdown of carbonic acid. the pH is buffered by influx of chloride. so as Co2 enters so does water
