Ion Transport Flashcards
Functions of Na+K+ ATPase pump
Forms Na and K gradients (need for electrical excitability)
VERY small (<5mV) resting membrane potential contribution
Drives secondary active transport
What is secondary active transport important for?
Control pH
Regulate cell volume and calcium levels
Absorption of sodium in epithelia
Nutrient uptake (glucose)
Why is intracellular calcium controlled?
Toxic to cells in high levels
Calcium and phosphate could crystallise
10,000-20,000 fold difference in levels across membrane (outside 50-100nM, inside 2mM)
How is calcium level of cell controlled?
PMCA (plasma membrane calcium ATPase)
SERCA (sarco/endoplasmic reticulum)
NCX (Na+Ca2+ exchanger)
Mitochondrial uniports
Ca2+ATPase function (PMCA)
PMCA expels Ca2+ out of cell and hydrogen into cell High affinity for Ca2+ Low capacity (removes residual)
PRIMARY ACTIVE
What does SERCA do? (Ca2+ATPase)
Drives Ca into endoplasmic/sarcoplasmic reticulum
H+ move out
High affinity, low capacity (removes residual)
PRIMARY ACTIVE
What does Na+Ca2+ exchange do? (NCX)
3Na in, Ca out
Low affinity, high capacity (removes most Ca2+)
SECONDARY ACTIVE
Facilitated transport to control calcium concentration
Mitochondrial uniporters
Operate at high calcium levels
Buffers to protect cell
Primary active transport controlling calcium levels
PMCA
SERCA
(Hydrogen in, calcium out)
Secondary active transport to control calcium levels
NCX
3 Sodium in, calcium out
Sodium calcium exchanger NCX importance
Cell toxicity during ischaemia/repurfusion
Electrogenic - current flows in direction of Na+gradient
Polarised cell NCX function
negative inside, positive outside
Calcium moves out
3 Sodiums move in
(High Ca in cell, low Na inside)
Depolarised cell NCX activity
Negative outside, positive inside
3 Sodiums move out, calcium moves in
(High Na in, Low Ca in)
REVERSE - important for cardiac action potential
Effects of Ischaemia on NCX
low O2 = low ATP
Na accumulates inside cell as not being pumped out
Cell depolarised
NCX reverses:
3 Na out, calcium in
Calcium TOXIC to cells in high levels
How is cell pH controlled
Make less acidic:
NHE (Na+H+ exchanger)
NBC (sodium bicarbonate cotransporter)
Make less basic:
Anion exchanger
NHE
Na+/H+ exchanger Na in, H out Electroneutral Regulates pH and cell volume Activated by growth factors
What is NHE inhibited by?
Amiloride
NBC
NBC - sodium bicarbonate chloride cotransporter
Hydrogen and chloride out
Sodium and bicarbonate in
= ALKALINE cell
Anion exchange (AE)
Bicarbonate (HCO3) out
Chloride in
ACIDIFIES
Two bicarbonate transporters
NBC Alkalinises
AE acidifies
Regulate pH and cell volume
How is pH controlled and balanced
Alkali environment activates AE
Acidification activates NHE and NBC
How is cell volume controlled
Swelling - extrude ions (water will move with)
Shrinking - influx ions (fill cell with ions and water)
Mechanisms to resist cell swelling and shrinking
Swelling: REMOVE IONS
Conductive systems
Co transport
Shrinking: FILL WITH IONS
Cotransport and conductive systems
