Vanadate inhibition of active Ca2+ transport across human red cell membranes.

(1) Vanadate (pentavalent vanadium) inhibits with high affinity (K0.5 = 3 microM) the ATP-dependent Ca2+ efflux in reconstituted ghosts from human red cell. (2) To inhibit Ca2+ efflux vanadate has to have access to the inner surface of the cell membrane (3) The inhibitory effect of vanadate is potentiated by intracellular Mg2+ and by intracellular K+. (4) Ca2+ in the external medium antagonizes the inhibitory effect of vanadate.