K+ transport in mitoplasts.

K+ transport into mitoplasts, prepared by digitonin disruption and removal of the outer membranes from rat liver mitochondria, has been studied. Unidirectional K+ influx has been measured by means of 42K, in the presence of the respiratory substrate succinate. K+ influx is inhibited by CN-, antimycin A and dicyclohexylcarbodiimide, but is insensitive to oligomycin. A linear dependence of the reciprocal of the K+ -influx rate on the reciprocal of the external K+ concentration is observed. Under the conditions studied, the apparent Km for K+ of the transport mechanism is approx. 6 mM, while the Vmax of K+ influx is approx. 5 mu mol K+/g protein per min. The rate of K+ influx increases with increasing external pH over the range from 6.8 to 8.0. The observed kinetics, pH dependence and inhibitor sensitivity are essentially similar to previously reported characteristics of K+ transport into intact rat liver mitochondria. It is concluded that the outer mitochondrial membrane does not not have a role in controlling K+ flux into rat liver mitochondria.