Influence of vanadate on calcium fluxes and net movement of calcium in intact squid axons

Intracellular vanadate at a concentration of 100 μM inhibits the uncoupled efflux of Ca²⁺ from intact axons but has little effect on the exchange fluxes and on the Ca²⁺-dependent Na⁺ efflux. External vanadate has no effect on the Ca²⁺ efflux. In addition and most importantly intracellular vanadate inhibits the Ca²⁺ efflux in the presence of external Na⁺ and Ca²⁺ suggesting that the uncoupled efflux is operative under physiological conditions. Measurements of the net movements of Ca²⁺ under near physiological conditions have confirmed this conclusion.