[Effect of calcium and other cations on pyruvate transport in rat liver mitochondria]

The effect of Ca2+ and other cations on the initial rate of pyruvate translocation by rat liver mitochondria has been studied. It has been found that added Ca2+ strongly stimulates the rate of pyruvate uptake by non-respiring mitochondria. Mn2+ and to lesser extent Sr2+ could replace Ca2+ whilst Mg2+ has only little effect. The stimulation of pyruvate uptake by Ca2+ is completely abolished by alpha-cyanocinnamate a specific inhibitor of pyruvate translocation but not by lanthanide which inhibits Ca2+ uptake. Direct measurements of the transmembrane delta pH in mitochondria show no appreciable changes following the addition of Ca2+, this excluding the possibility that the Ca2+ dependent stimulation of pyruvate uptake might be due to an increase of transmembrane delta pH. It is therefore conceivable that the effect of Ca2+ can be ascribed to an interaction of this cation with the translocator on the external of the mitochondrial membrane. Although the data obtained do not warrant postulation of the nature of the calcium induced stimulation of mitochondrial pyruvate transport it is likely that this effect may be of a great importance in the regulation of pyruvate transport and metabolism in mitochondria.