Ion Transport in Liver Mitochondria

The role of surface binding on the Ca++ translocation in mitochondria has been studied. The Ca++ bound at the mitochondrial surface in the absence of respiration is translocated to the inner mitochondrial spaces at the initiation of respiration. Impermeant cations, which compete with Ca++ for the binding at the mitochondrial surface, also affect the rate of aerobic Ca++ translocation. The initial rates of aerobic Ca++ uptake and of related processes, such as H+ release and oxygen consumption, are about 40% slower in 0.125 m KCl than in 0.25 m sucrose. Inhibition by K+ of the surface binding and of the rate of Ca++ translocation parallel each other although the degree of inhibition is higher in the former process. Surface binding of Ca++ is also reduced by the addition of Mg++, by lowering the pH, or by increasing the osmolarity of the medium, and the rates of oxygen uptake and H+ release undergo a parallel decrease. The effect of surface binding on the aerobic stoichiometries and the mechanism of Ca++ translocation are discussed.