Mitochondrial swelling induced by Ca2+ and inorganic phosphate and its related phenomena

Some investigations have been done on the relationships between the swelling-shrinkage change, oxygen consumption and state of oxidation-reduction of pyridine nucleotides of mitochondria, and between the swelling-shrinkage change of mitochondrial structure by Ca2+ and accumlation of Ca45 in rat liver mitochondria. A parallel relationship is observed between the Ca2+ induced swelling and Ca2+ accumulation. Both of them require Pi but not Mg2+, ATP and exogenous respiratory substrates and are inhibited by respiratory inhihitors or uncouplers of oxidative phosphorylation but not by the inhibitors of phosphorylating respiration. In this case the Ca2+ is transported with the phosphate even in ice cold. Even in the presence of antimycin A, moreover, Pi-dependent Ca2+ accumulation and Ca2+ induced swelling can be overcome by addition of ATP, which are inhibited by oligomycin. In the presence of Pi, mitochondria show shrinkage by addition of Ca2+ before the high amplitude swelling, which is closely correlated to the electron ransport chain and phosphorylation process of mitochondria, and the pattern of the mitochondrial shrinkage is quite similar to that observed in the case of respiratory control by ADP in intact mitochondria. This shrinkage of mitochondria is inhibited by respiratory inhibitor or uncoupler of oxidative phosphorylation but not by the inhibitor of phosphorylating respiration. From these data, therefore, it is considerd that the Ca2+ accumulation and Ca2+ induced shrinkage-swelling of mitochondria require the energy of oxidative phosphorylation with respect to the initial step before the oligomycin block.