Glycolytic regulation during an aerobic rest-to-work transition in dog gracilis muscle

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Abstract
Glycogen phosphorylase activity and several glycolytic intermediates were measured at rest and after 5, 10, 15, 30, 60, and 180 s of twitch stimulation at 4 Hz in fast-frozen samples of gracilis muscle. During an initial burst of glycolysis (0–5 s) only 3-phosphoglycerate and lactate accumulate. These changes are reversed during the period of low glycolytic flux (5–30 s). During a second burst of glycolysis (30–60 s) most glycolytic intermediates increase. The levels of glycogen phosphorylase a changes in parallel with the initial burst of glycolysis but remain at resting levels throughout the second burst. The phosphoglycerate mutase-enolase steps deviate from equilibrium during the initial burst of glycolysis, suggesting a transiently rate-limiting role. Analysis using a model of phosphofructokinase kinetics indicates that combined changes in cytosolic pH (R. J. Connett, J. Appl. Physiol. 63: 2360–2365, 1987) and free [ADP] and [AMP] can account for the initial burst of glycolysis. The second burst of glycolysis requires other regulatory factors. It is concluded that an initial alkalization is a major regulatory factor in the early burst of glycolysis during a rest-to-work transition in red muscle.