Monovalent cation conductance in liposomes induced by ionophore A23187.

In the absence of divalent cations, ionophore A23187 supports low rates of monovalent cations loss (Na+ greater than K+) from unilamellar liposomes containing the sulfate salts. Monovalent cation efflux is optimal when a pH gradient (interior alkaline) is applied. The maximum observed rate of 0.56 ngion K+ . min-1 . nmol-1 A23187 is insufficient to account for the rates of K+ efflux induced by the ionophore in mitochondria (150 ngion K+ . min-1 . nmol-1 A23187). These studies therefore support the concept that A23187 induces loss of K+ from mitochondria by removal of regulating divalent cations from an endogenous K+/H+ exchanger.