The relation between muscle contraction and metabolism: studies by 31P nuclear magnetic resonance spectroscopy.

We have used 31P nuclear magnetic resonance spectroscopy (31PNMRS) to study the relation between metabolism and contraction in frog skeletal muscle. Our results show a close association between [H2PO4(1-)] and both contractile and metabolic characteristics of muscle. We suggest that this metabolite links energy requiring to energy yielding function by participating in intermediate reactions which help to determine the rates of both processes. The observed relation between [H2PO4(1-)] and force production is consistent with the suggestion of Hibberd and colleagues, that Pi is reversibly released during the transition to the major force-producing actomyosin ATPase state. Our results also suggest that force fatigue is due to the buildup of the [H2PO4(1-)] product of ATP hydrolysis and that the effect of pH on force production is largely the result of altering H2PO4(1-)/HPO4(2-). We have found that it is the extent of glycogenolysis rather than the maximum activities of glycogenolytic enzymes that determines how much glycogen is broken down following anaerobic contraction. The most likely explanation for our results is that the ATP-forming reactions of glycolysis come to equilibrium during metabolic recovery from contraction under anaerobic conditions.