ENERGY USE BY CONTRACTILE AND NONCONTRACTILE PROCESSES IN SKELETAL-MUSCLE ESTIMATED BY P-31-NMR

The goal of this study was to separately determine ATP use by contract ile and noncontractile processes in stimulated skeletal muscle. ATP us e by tetanically stimulated bullfrog semitendinosus muscle was monitor ed at room temperature with in vivo P-31-nuclear magnetic resonance. O xidative phosphorylation was inhibited by cyanide, and ATP use could t herefore be calculated by accounting for ATP derived from the creatine kinase (CK) reaction (measured from decreases in phosphocreatine) and from glycolysis (estimated from decreases of intracellular pH). In un fatigued muscles stimulated at optimal length for force production, to tal ATP utilization (representing both contractile and noncontractile processes) was 2.5 +/- 0.09 (SE) mM/s (n = 6; 53% ATP from glycolysis, 47% from CK). In separate experiments, cross-bridge interactions betw een actin and myosin filaments were eliminated by increasing sarcomere length; therefore, with stimulation, residual ATP use reflected only noncontractile processes. In stimulated stretched muscles, ATP utiliza tion was reduced compared with unstretched muscles to 1.07 +/- 0.08 mM /s (61% ATP from glycolysis, 39% from CK). These findings suggest that , during contraction near optimum length, a large proportion (similar to 43%) of ATP is used by noncontractile processes, with more ATP deri ved from glycolysis than from CK.