Vasopressin and/or glucagon rapidly increases mitochondrial calcium and oxidative enzyme activities in the perfused rat liver.

Mitochondria were prepared by a method including a Percoll purification step after the rapid homogenization of livers of fed rats which had been perfused either under unstimulated conditions or in the presence of vasopressin and/or glucagon. The two hormones separately or together increased the total calcium content of the mitochondria. This enhancement was accompanied by parallel increases in activities of the Ca2+-sensitive intramitochondrial enzymes pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase. The effects of the two hormones on total mitochondrial calcium and on the activities of the oxidative enzymes were additive. The persistent enhancements of mitochondrial calcium content and enzyme activities were partially reversed by the addition of Na+ ions to the mitochondrial incubations; these effects of Na+ were blocked by diltiazem, a selective inhibitor of Na+-induced Ca2+ release. Mitochondria from control livers were incubated in vitro with CaCl2 to achieve various calcium content, and mitochondrial enzyme activities and calcium content were measured. A good correlation was obtained between the total calcium content and the activities of pyruvate dehydrogenase and oxoglutarate dehydrogenase. The results obtained are consistent with the hypothesis that vasopressin and glucagon additively cause increases in intramitochondrial [Ca2+] and so bring about the activations of these key enzymes of mitochondrial oxidative metabolism.