Characteristics of the movement of K+ across the mitochondrial membrane and the inhibitory action of Tl+.

The incubation of mitochondria in mixtures that contain phosphate, NaCl, oxidizable substrate, and ethylenediaminetetraacetate induces the efflux of K-+. This process depends on electron transport and on the cyclic movement of phosphate across the membrane. Sodium ions, Li-+, or Cs-+ to a smaller extent, are required for maximal release of K-+. Potassium ions do not induce net efflux of internal K-+, but instead prevent the Na-+-induced release of K-+. Significant K-+ influx takes place in K-+-depleted mitochondria through a process with characteristics which are almost identical with those in which K-+ release takes place. As Na-+ inhibits the uptake of K-+, it is suggested that the movement of K-+ across the membrane is controlled by the cationic environment. Thallous ion, at concentrations that do not affect oxidative phosphorylation, was found to be an effective inhibitor of the influx and the efflux of K-+. The inhibitory effect of Tl-+ seems to be specific for K-+ since it does not affect the movement of Na-+. Mitochondria bind 10 to 15 nmol of 204-Tl-+ per mg of protein through an energy-independent process.