ACTIVATION OF GLYCOLYSIS IN HUMAN MUSCLE IN-VIVO

We tested the cytoplasmic control mechanisms for glycolytic ATP synthe sis in human wrist flexor muscles. The forearm was made ischemic and a ctivated by maximal twitch stimulation of the median and ulnar nerves in 10 subjects. Kinetic changes in phosphocreatine, P-i, ADP, ATP, sug ar phosphates, and pH were measured by P-31 magnetic resonance spectro scopy at 7.1-s intervals. Proton production was determined from pH and tissue buffer capacity during stimulation. Glycolysis was activated b etween 30 and 50 stimulations, and the rate did not significantly chan ge through the stimulation period. The independence of glycolytic rate on [P-i], [ADP], or [AMP] indicates that feedback regulation by these metabolites could not account for this activation of glycolysis. Howe ver, glycolytic H+ and ATP production increased sixfold from 0.5 to 3 Hz, indicating that glycolytic rate reflected muscle activation freque ncy. This dependence of glycolytic rate on muscle stimulation frequenc y and independence on metabolite levels is consistent with control of glycolysis by Ca2+.