Mitochondrial calcium release as induced by Hg2+

Addition of Hg2+ to mitochondria of rat kidney induces efflux of intramitochondrial Ca2+. This reaction is accompanied by a diminution of the NAD(P)H/NAD(P) ratio and a decrease of the internal negative membrane potential. These effects were enhanced by dithiothreitol. The binding of mercuric ions to mitochondria saturates with a maximal binding of 9 nmol min-1 mg-1. The stoichiometry between Ca2+ released and Hg2+ bound showed that in the presence of dithiothreitol, the binding of approximately 1 nmol of Hg2+/mg of protein suffices to induce the release of the accumulated Ca2+. In the electrophoretic analysis of Hg-labeled mitochondrial proteins it was found that 203Hg2+ bound mainly to proteins that have molecular masses of 20 and 30 kDa. It is proposed that Hg2+-induced Ca2+ release is due to modification of--SH groups of these latter proteins.