PH AND TEMPERATURE EFFECTS ON KINETICS OF CREATINE-KINASE IN AQUEOUS-SOLUTION AND IN ISOVOLUMIC PERFUSED HEART - A P-31 NUCLEAR MAGNETIZATION-TRANSFER STUDY

Phosphorylated metabolites concentrations and creatine kinase kinetics are measured by P-31 NMR in solution and in isovolumic perfused rat hearts submitted to hypo- and hyperthermia as well as to acidosis (37-degrees-C). In the organ, temperature variation from 40 to 25-degrees-C induces an increase of phosphocreatine (PCr) stores, a decrease of P(i) and ADP concentrations, but does not affect the ATP pool. Creatine kinase forward flux (V(for)) is gradually reduced when the temperature is lowered both in vitro and in perfused heart. In normothermic and hypothermic conditions, a relationship is found between cardiac performance (rate pressure product, RPP), V(for) and ATP synthesis estimated through the myocardial oxygen consumption rate (MVO2). At 40-degrees-C however, the RPP is reduced although both V(for) and MVO2 increase. In vitro experiments show an optimum pH of 7.7 for the forward creatine kinase reaction. In perfused heart submitted to acidosis, a decrease of PCr concentration is observed, whereas ATP and ADP contents remain unchanged. Heart creatine kinase flux increased as in hyperthermia. These high fluxes are attributed to the coupling of the creatine kinase reaction with energy consuming or producing reactions: the increase of energy demand related to non-contractile processes could explain the high MVO2 and V(for) observed in those conditions.