INVOLVEMENT OF ENDOGENOUS PHOSPHOLIPASE-A2 IN CA2+ AND MG2+ MOVEMENTS INDUCED BY INORGANIC-PHOSPHATE AND DIAMIDE IN RAT-LIVER MITOCHONDRIA

Addition to rat liver mitochondria of 2 mM inorganic phosphate or 0.15 mM diamide, a thiol oxidizing agent, induced a respiration dependent efflux of Mg2+ which was prevented by both antimycin A and tetracaine. Tetracaine also inhibited the release of respiration induced by phosphate or diamide. Endogenous Ca2+ were retained by mitochondria until 50-60 per cent of endogenous Mg2+ has been lost. Tetracaine retarded Ca2+ release. The involvement of mitochondrial phospholipase A2 is demonstrated both by its inhibition by tetracaine and its activation by diamide or phosphate. The failure of these compounds to activate phospholipase A2 in the presence of added Ca2+ makes reasonable the assumption that the activation of phospholipase A2 is secondary to respiration dependent Ca2+ movements, which would favour the interaction Ca2+-phospholipase A2. © 1979.