Glycolysis in contracting rat skeletal muscle is controlled by factors related to energy state
Résumé
The control of glycolysis in contracting muscle is not fully understood. The aim of the present study was to examine whether activation of glycolysis is mediated by factors related to energy state or by a direct effect of Ca2+ on the regulating enzymes. Extensor digitorum longus muscles from rat were isolated, treated with cyanide to inhibit aerobic ATP production and stimulated (0.2s trains every 4s) until force was reduced to 70% of initial force (Con). Muscles treated with BTS, an inhibitor of cross-bridge cycling without affecting Ca2+ transients, were stimulated for an equal time as Con. Energy utilization by the contractile apparatus (estimated from the observed relation between ATP utilization and force-time integral) was 60% of total. In BTS force-time integral and ATP utilization was only 38% and 58% of that in Con, respectively. Glycolytic rate in BTS was only 51% of that in Con but the relative contribution of ATP derived from PCr and glycolysis and the relation between muscle contents of PCr and lactate were not different. Prolonged cyanide incubation of quiescent muscle (low Ca2+), did not change the relation between PCr and lactate. The reduced glycolytic rate in BTS despite maintained Ca2+ transients, and the unchanged PCr/Lactate relation in the absence of Ca2+ transients, demonstrates that Ca2+ is not the main trigger of glycogenolysis. Instead the preserved relative contribution of energy delivered from PCr and glycolysis during both conditions suggests that the glycolytic rate is controlled by factors related to energy state.
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