KINETICS OF CREATINE-KINASE IN AN EXPERIMENTAL-MODEL OF LOW PHOSPHOCREATINE AND ATP IN THE NORMOXIC HEART

To study the dependence of the forward flux of creatine kinase (CK) on its substrates and products we designed an acute normoxic model of st eady-state depletion of phosphocreatine (PCr) and adenylate in the iso volumic acetate-perfused rat heart. Various concentrations of PCr and ATP were induced by prior perfusion with 2 deoxy-D-glucose in the pres ence of insulin. The apparent rate constant (K-f) and the forward CK f lux were measured under metabolic and contractile steady state by prog ressive saturation-transfer P-31 nuclear magnetic resonance (NMR). At high adenylate content CK flux was constant for a twofold reduction in PCr concentration ([PCr]); CK flux was 6.3 +/- 0.6 mM/s (vs. 6.5 +/- 0.2 mM/s in control) because of a doubling of k(f). Although, at the l owest ATP concentration and [PCr], CK flux was reduced by 50%, it neve rtheless always remained higher than ATP synthesis estimated by parall el oxygen consumption measurement. NMR-measured flux was compared with the flux computed under the hypothesis of CK equilibrium. CK flux cou ld not be fully predicted by the concentrations of CK metabolites. Thi s is discussed in terms of metabolite and CK isozyme compartmentation.