The K+ conductance of the inner mitochondrial membrane. A study of the inducible uniport for monovalent cations.

Addition of A23187 plus EDTA to rat liver mitochondria induces a common uniport pathway for monovalent cations. In this study, we have carried out a detailed characterization of the flow/force relationship for K+ transport along this pathway under steady state conditions. In the presence of EDTA, the K+ conductance is a linear function of external K+ in the range 0-20 mM K+, with a slope of 0.15 nmol of K+ x mg of protein-1 x min-1 x mV-1. The K+ conductance is inhibited by Mg2+ in the range 10(-9)-10(-6) M, while K+ flux is stimulated by the sulfhydryl group reagent mersalyl. Uniport activity can be detected in native mitochondria. These findings are compatible with the notion that electrophoretic K+ flux across the inner membrane takes place via a regulated K+ uniport with the potential of transporting K+ at rates in excess of 600 nmol x mg of protein-1 x min-1.