The energetics of myocardial stretch: Creatine kinase flux and oxygen consumption in the noncontracting rat heart

Abstract

Previous studies have suggested that flux through the creatine kinase reaction is coupled to cardiac performance and to the rate of adenosine triphosphate synthesis in the intact, beating heart. To define the effect of passive myocardial stretch on creatine kinase kinetics, we measured the rate constants and chemical fluxes for both directions of the creatine kinase reaction with the 31P-nuclear magnetic resonance technique of magnetization transfer in isolated, arrested rat hearts at four levels of left ventricular pressure and volume. Adenosine triphosphate synthesis was estimated from oxygen consumption measurements. As left ventricular pressure rose from 0 to 24 mm Hg and oxygen consumption increased by 20%, we observed a twofold increase in the rate constants and fluxes (mean ± SD, n = 4-7) for the creatine kinase reaction. The forward rate constant increased from 0.33 ± 0.03 to 0.80 ± 0.08, and the reverse rate increased from 0.34 ± 0.11 to 0.74 ± 0.32/sec. The forward and reverse fluxes for the creatine kinase reaction increased from 12.0 ± 3.4 to 26.5 ± 5.8 and from 9.1 ± 3.4 to 19.1 ± 3.4 μmol/g dry weight per sec, respectively. At each level of left ventricular pressure, the forward and reverse rate constants were the same. However, as left ventricular pressure increased, the ratio of the forward to the apparent reverse fluxes for the creatine kinase reaction increased. The relationships between the rate constant or flux through the creatine kinase reaction vs. left ventricular pressure were linear. In addition to providing further support for the coupling between creatine kinase and mitochondrial adenosine triphosphate synthesis, these results suggest that flux through the creatine kinase reaction and adenosine triphosphate synthesis increases with myocardial stretch in the intact, noncontracting heart.