J. Biol. Chem., Vol. 261, Issue 19, 8799-8804, Jul, 1986
Vasopressin and/or glucagon rapidly increases mitochondrial calcium and oxidative enzyme activities in the perfused rat liver
F Assimacopoulos-Jeannet, JG McCormack and B Jeanrenaud
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.