Influence of ATP turnover and metabolite changes on IMP formation and glycolysis in rat skeletal muscle.

Deamination of AMP to inosine monophosphate (IMP) and NH3 is thought to be regulated by the observed increases in ADP, AMP, and H+. We have examined this hypothesis by comparing the rate of IMP accumulation in contracting and noncontracting rat skeletal muscle. The rate of IMP formation was high during ischemic contraction, and consistent with previous studies, formation of IMP was associated with high levels of muscle lactate, depletion of phosphocreatine (PCr), and increased levels of ADP and AMP. When the contraction period was followed by 5-min anoxic recovery, the metabolic changes were maintained, but no further IMP or lactate was formed. During long-term (2-4 h) anoxia, the rate of IMP formation was less than 4% of that during contraction, despite similar changes in PCr, lactate, ADP, and AMP. It is concluded that the observed changes in the intracellular chemical environment are not sufficient to explain the high rate of IMP formation during contraction but that a combination of metabolic stress and a high ATP turnover rate is required. It is suggested that a high ATP turnover rate during conditions of metabolic stress results in transient increases in ADP and AMP at the site of ATP hydrolysis and that these activate AMP deaminase and glycolysis. An alternative hypothesis is that these processes are regulated by the increase in cytosolic Ca2+ in a contracting muscle.