Changes in membrane potential during calcium ion influx and efflux across the mitochondrial membrane.
1. A depolarisation of the membrane of rat liver mitochondria, as measured with the safranine method, is seen during Ca2+ uptake. The depolarisation is followed by a slow repolarisation, the rate of which can be increased by the addition of EGTA or phosphate. 2. Plots relating the initial rate of calcium ion (Ca2+) uptake and the decrease in membrane potential (delta psi) to the Ca2+ concentration show a half-maximal change at less than 10 micron Ca2+ and a saturation above 20 micron Ca2+. 3. Plots relating the initial rate of Ca2+ uptake to delta psi are linear. 4. Addition of Ca2+ chelators, nitriloacetate or EGTA, to deenergized mitochondria equilibrated with Ca2+ causes a polarisation of the mitochondrial membrane due to a diffusion potential created by electrogenic Ca2+ efflux. 5. If the extent of the response induced by different nitriloacetate concentrations is plotted against the expected membrane potential a linear plot is obtained up to 70 mV with a slope corresponding to two-times the extent of the response induced by valinomycin in the presence of different potassium ion gradients. This suggests that the Ca2+ ion is transferred across the membrane with one net positive charge in present conditions.
D000085:Acetates / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D004058:Diffusion; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000378:metabolism*; D051381:Rats
D000085:Acetates; D004533:Egtazic Acid; D002118:Calcium