IMP METABOLISM IN HUMAN SKELETAL-MUSCLE AFTER EXHAUSTIVE EXERCISE

This study addressed whether AMP deaminase (AMPD):myosin binding occur s with deamination during intense exercise in humans and the extent of purine loss from muscle during the initial minutes of recovery. Male subjects performed cycle exercise (265 +/- 2 W for 4.39 +/- 0.04 min) to stimulate muscle inosine 5'-monophosphate (IMP) formation. After ex ercise, blood flow to one leg was occluded. Muscle biopsies (vastus la teralis) were taken before and 3.6 +/- 0.2 min after exercise from the occluded leg and 0.7 +/- 0.0, 1.1 +/- 0.0, and 2.9 +/- 0.1 min postex ercise in the nonoccluded leg. Exercise activated AMPD; at exhaustion IMP was 3.5 +/- 0.4 mmol/kg dry muscle. Before exercise, 16.0 +/- 1.6% of AMPD cosedimented with the myosin fraction; the extent of AMPD:myo sin binding was unchanged by exercise. Inosine content increased about threefold during exercise and twofold more during recovery; by 2.9 mi n postexercise it was 0.43 +/- 0.02 mmol/kg dry muscle. IMP decreased 2.1 +/- 0.3 mmol/kg dry muscle with no change in total adenylates. Tot al purines declined significantly (P < 0.05) during the recovery perio d in the nonoccluded leg, consistent with a loss of purines to the cir culation, whereas total purines were unchanged in the occluded leg. Re gulation of muscle purine content is a dynamic process that must accom modate rapid changes due to degradation and efflux.