Metabolic-independent volume changes and Mg++ binding in mitochondria isolated from AH-130 Yoshida ascites hepatoma.

Mitochondria isolated from AH-130 Yoshida ascites hepatoma appear spontaneously swollen. In these mitochondria, the metabolic-dependent swelling induced by phosphate and the metabolic-independent swelling induced by digitonin occur to a very small extent. In the swollen mitochondria, evident shrinkage may be induced by adding Mg++ ions in the absence of exogenous ATP. This shrinkage has been determined by spectrophotometric as well as by water content and packed volume measurements. The shrinkage, which occurs in metabolizing and in metabolically inhibited mitochondria, is not reversed either by diluting the external Mg++ concentration in the mitochondrial suspension or by washing the mitochondria after incubation in the presence of the bivalent cation. At the same time as the shrinkage, there occurs a passive uptake of Mg++ by tumor mitochondria. There is evidence that a fraction of the Mg++ taken up is firmly bound to the mitochondrial surface. Both the Mg++ binding and the Mg++-induced shrinkage have some common features, chiefly their sensitivity to inhibition by KCl present in the medium. Our findings suggest that the Mg++-induced shrinkage in tumor mitochondria is related to the irreversible binding of the bivalent cation to the membranes of the mitochondria.