6. ATP Dependent Pumps And Ion Exchangers Flashcards
Na+/K+ - ATPase functions
Forms Na+ and K+ gradients
Pumps 3 Na+ out for every 2 K+ in
Drives secondary active transport
Intracellular calcium
Large difference in levels across plasma membrane (higher outside)
High intracellular is toxic
Cells signal by small changes in intracellular calcium
Control of resting Ca2+
Primary active transport:
- PMCA expels Ca2+ out of cell
- SERCA accumulates Ca2+ into SR/ER
- high affinity, low capacity, removes residual Ca2+
Secondary active transport:
- NCX
- low affinity, high capacity, removes most Ca2+
Facilitated transport:
- mitochondrial Ca2+ uniports
- operate at high Ca2+, buffer
Sodium calcium exchanger (NCX)
Exchanges 3 Na+ in for 1 Ca2+ out
Electrogenic
Role in expelling intracellular Ca2+ during cell recovery
Role in cell toxicity during ischaemia/reperfusion
Membrane potential dependent - depolarised membrane potential reverses mode of operation
Ischaemia - role of NCX
Sodium pump inhibited Na+ accumulates Cell depolarises NCX reverses Na+ in for Ca2+ out
Control of cell pH - acid extruders
Na+/H+ exchanger (NHE)
Na+ dependent Cl-/HCO3- exchanger (NBC)
Control of cell pH - base extruders
Cl-/HCO3- exchanger (AE)
Na+/H+ exchanger (NHE)
Exchanges extracellular Na+ for intracellular H+ Electroneutral 1:1 exchange Regulates pHin Regulates cell volume Activated by growth factors Inhibited by a milo ride
Bicarbonate transporters - NBC
Sodium bicarbonate chloride cotransporter Sodium and bicarbonate in Hydrogen and chloride out Alkalinises cell Cell volume regulation
Bicarbonate transporters - AE
Anion exchanger
Bicarbonate out, chloride in
Acidifies cell
Cell volume regulation
Intracellular pH regulation
pH held at set point
Any drift away from pH is corrected by increased activity of Na+-H+ or Cl-HCO3- exchangers
Cell volume regulation
Transport of osmotically active ions (K+, Na+, Cl-)
Water follows
If cell swelling, extrude ions
If cell shrinking, influx ions
Regulation of cell volume
Different cell types use particular combinations of transporters to achieve regulation they need
Renal anti-hypertensive therapy in thick ascending limb
Loop diuretics block sodium-potassium-chloride co transporters (NKCC2)
Renal anti-hypertensive therapy in distal convoluted tubule
Thiazides block sodium-chloride cotransporter (NCCT)
Amiloride blocks epithelium sodium channel
