METABOLIC FLUCTUATION DURING A MUSCLE-CONTRACTION CYCLE

Gated P-31-nuclear magnetic resonance followed the metabolic fluctuati on in rat gastrocnemius muscle during a contraction cycle. Within 16 m s after stimulation, the phosphocreatine (PCr) level drops 11.3% from its reference state. The PCr minimum corresponds closely to the time o f maximum force contraction. P-i increases stoichiometrically, while A TP remains constant. During a twitch, PCr hydrolysis produces 3.1 mu m ol ATP/g tissue, which is substantially higher than the reported 0.3 m u mol ATP.twitch(-1).g tissue(-1) derived from steady-state experiment s. The results reveal that a substantial energy fluctuation accompanie s a muscle twitch.