Active Transport of Potassium Ion in Heart Mitochondria

Abstract

Several factors affecting K + transport by rabbit heart mitochondria were examined, using a K + -sensitive electrode. The histone fractions f 2 a and β-7 produced an energy-dependent efflux of K + . Inorganic phosphate was required for optimal activity; K m for phosphate was 60 µ M . Both rate and extent of K + efflux decreased as K + concentration in the reaction medium was increased. The direction of valinomycin-induced K + movements was shown to depend on the net resultant of an active transport mechanism and increased membrane permeability. The detergent triton X-100 produced a nonspecific increase in membrane permeability that led to a rapid efflux of K + . Evidence is presented for competition between ion transport and ATP formation for some common energy intermediate. Possible mechanisms of action of histones and other agents affecting heart mitochondrial K + transport are considered.