Mitochondrial calcium transport and calcium-activated phospholipase in porcine malignant hyperthermia

The interaction of Ca2+ with mitochondria isolated from longissismus dorsi, a predominantly white skeletal muscle, of normal and malignant hyperthermia pigs was investigated using tightly-coupled preparations. Arrhenius plots of mitochondrial Ca2+ -stimulated respiration for succinate oxidation of malignant hyperthermia pigs showed a transition temperature (Tt) of 26.31 +/- 0.80 degrees C (n = 5), which was decreased by spermine to 15.41 +/- 0.69 degrees C (n = 3), a value very similar to that for normal pigs. No difference in either the Tt or in the activation energy (Ea) was observed between the two types of pigs when ADP was used instead of Ca2+. Mitochondria of malignant hyperthermia pigs were uncoupled at 40 degrees C by exogenous Ca2+ at 1221 +/- 301 (n = 9) nmol Ca2+ per mg proteinn during succinate oxidation and the uncoupled mitochondria showed large amplitude swelling. Both the Ca2+ -induced uncoupling and swelling were prevented by bovine serum albumin and by the phospholipase inhibitors, spermine and tetracaine. In contrast, mitochondria of normal pigs were still tightly coupled even after a total addition of 2313 +/- 287 (n = 5) nmol Ca2+ per mg protein and retained the original condensed configuration in the presence or absence of spermine and tetracaine. Mitochondria of malignant hyperthermia pigs contained significantly (P less than 0.001) higher quantities of endogenous Ca2+ and showed a significantly (P less than 0.001) faster FCCP-induced endogenous Ca2+ efflux rate than normal when monitored spectroscopically with murexide. No significant difference was observed in either the rate of exogenous Ca2+ uptake or in the extent of Ca2+ accumulated in the aerobic steady state during succinate oxidation between the two types of pigs. The rate of mitochondrial Ca2+ efflux of malignant hyperthermia pigs during anaerobiosis was about twice that of normal. Experimental evidence suggests that mitochondria from musculi longissimus dorsi of malignant hyperthermia pigs contained a Ca2+ -stimulated phospholipase A2 (EC 3.1.1.4, phosphatide 2-acylhydrolase), and that this enzyme if present in mitochondria of normal pigs is either latent or in very low concentration. The significance of the Ca2+ -stimulated phospholipase A2 and its association with the enhanced rate of glycolysis in porcine malignant hyperthermia syndrome and in the post-mortem formation of the pale, soft and exudative conditions observed in white skeletal muscles of malignant hyperthermia pigs is discussed.