Ion Transport in Liver Mitochondria

Addition of small amounts of Ca++ to liver mitochondria incubated in the absence of phosphate or acetate results in an inhibition of respiration. The inhibition of respiration is reversed by increasing the concentration of substrate anions in the medium, and is enhanced by increasing the ionic strength or the pH of the medium. The H+:O and Ca++:O ratios are increased severalfold when measured under conditions of inhibited respiration. Furthermore, mitochondria which have entered a state of inhibited respiration continue to take up Ca++ and to release H+. It is concluded that the above stoichiometries in the absence of phosphate or acetate are determined by both uninhibited and inhibited respirations. The higher the concentration of Ca++, the larger is the contribution of the inhibited respiration. In the presence of acetate, the Ca++ to total oxygen ratio is in the region of 2.0 to 2.5 with succinate as substrate. The inhibition of respiration is related to the increase of the intramitochondrial pH as followed kinetically with the bromthymol blue technique. The bromthymol blue response is dependent on the rate of influx of anions. Increasing the ionic strength and pH enhances the bromthymol blue response, presumably by restraining the influx of anions. The mechanism by which the inhibition of respiration causes the superstoichiometric ratios is discussed.