Lecture 6- ATP- dependent pumps and ion exchangers Flashcards
function of sodium pump (Na+/K+ ATPase)
- forms sodium and potassium gradient
- necessary for electrical excitability
- drives secondary active transport
secondary ative transport
active transporters powered by the gradient created by another reactive transporter e.g. the Na pump when sodium powers other transporters
e.g. Na/H+ or Na/Ca2+ or Na/glucose or Na/amino acid symports
sodium pump (Na+/K+ ATPase) also has roles in
o Control of pH
o Regulation of cell volume and calcium
o Absorption of Na in epithelia
o Nutrient uptake e.g. glucose from SA
intracellular calcium is
very low (0.1 um)
where is calcium high
in the ER/SR and extracellular environment (2mM)
- 10,000-20,000 fold difference across plasma membrane
high intracelliular calcium is
toxic to cells
why is high intracellular calcium toxic
preventing calcium phosphate from forming- ossification of tissues
and
can cause ischaemia
cells signal by small changes in
intracellular calcium
control of intracellular calcium
Na/Ca exchanger, PMCA andSERCA
Na+/Ca2+ exchanger
secondary active transport
- powered by the sodium gradient created by the sodium pump (Na+/K+ ATPase)
- pumps calcium out of the cell
PMCA stands for
plasma membrane Ca2+ ATPase
- exchanges calcium for H+
SERCA stands for
Sarcoplasmic reticulum pump Ca2+ ATPase
- pumps calciums into intracellular stores e.g. the SR
calcium uniporters
use electrical gradient to pump calcium into the mitochondria
Control of calcium: primary active transport
- PMCA
- SERCA
PMCA- affinity and capacity?
high affinity
low capacity- removes residual calcium
SERCA - affinity and capacity?
high affinity
low capacity- removes residual calcium
Secondary active transport
Na/Ca exchanger (NCX)
NCX - affinity and capacity?
low affinity
high capacity
- removes most calcium
mitochondrial calcium uniporters
operate at high calcium to buffer damaging calcium
more detail on the sodium calcium exchanger (NCX)
- Secondary active transporter
- Exchanges 3 sodium’s for 1 calcium
- Membrane potential dependent
when the membrane is polarised
High calcium inside
Low sodium inside
when the membrane is depolarised
high sodium inside
low calcium inside
NXC in ischaemia
- ATP depleted- sodium pump (Na+/K+ ATPase) inhibited
- Na+ accumulates
- Cell depolarised
- Causes sodium calcium exchange to reverse action
- Sodium comes in instead of out and calcium goes out the cell
- High Calcium conc is toxic
ion channels can be used to control cell pH using
Acid and base extruders
acid extruders - give example
attempt to increase the pH of the cell- alkalinises
- Na+/H+ exchanger (NHE)
- sodium bicarbonate exchanger (NBC)
base extruders- give example
Attempts to decrease the pH of the cell- acidified
- Anion exchanger
normal pH of cell
7.35-7.45
cell volume regulation
no standard method for cell volume regulation- diff cell types use diff combinations of transporters to achieve the regulation they need
water follows
ions
high osmolarity
water will flow into cell
low osmolarity
water will leave cell
cell swelling will
extrude ions
e.g. potassium chloride co-transporter
cell shrinking
influx ions
e.g. sodium-chloride co transporters
