[Oxaloacetate-dependent calcium transport in rat liver mitochondria].

The effect of oxaloacetate on Ca2+ transport in isolated rat liver mitochondria has been studied. Under aerobic conditions in the presence of oxaloacetate mitochondria accumulate Ca2+ in a ruthenium red- and uncoupler-sensitive way. Oxaloacetate catalyzes also the slow (5 nM Ca2+/min/mg protein) uptake of limited amounts of calcium by the mitochondria in the presence of respiratory chain and ATPase inhibitors. Under these conditions ADP, pyruvate, succinate and isocitrate increase both the rate of oxaloacetate-dependent Ca2+ transport and the amount of the accumulated cation. In all cases studied (with the exception of isocitrate) the oxaloacetate-dependent Ca2+ uptake was blocked by low concentrations of arsenite. Oxaloacetate added to mitochondria in the presence of respiratory chain and ATPase inhibitors increases the [NAD+]. [NADPH]/[NADH].[NADP+] ratio and stimulates the transmembrane potential generation in the mitochondria. Ammonium chloride decreases the rates of the oxaloacetate-dependent Ca2+ uptake. The data obtained suggest that the oxaloacetate-dependent Ca2+ uptake by the mitochondria first demonstrated in this study is mediated by energy-dependent mitochondria transhydrogenase. These results are discussed in connection with oxaloacetate-induced Ca2+ release from mitochondria.