CHEMICAL-CHANGE AND ENERGY-PRODUCTION DURING CONTRACTION OF FROG-MUSCLE - HOW ARE THEIR TIME COURSES RELATED

Abstract

The heat + work (h + w) and the changes in the levels of creatine, phosphocreatine and ATP were determined for 1, 2, 5, 10 and 15 s isometric tetani at 0.degree. C under aerobic conditions. The change in the sum of Pi, glucose-1-phosphate and glucose-6-phosphate was measured. The changes in the levels of all these chemicals and of lactate were measured in muscles stimulated for 15 s under anaerobic conditions. The lactate measurements and a comparison of the results for aerobic and anaerobic conditions showed that during a 15 s tetanus there was a negligible amount of resynthesis of ATP from reactions other than the creatine kinase reaction. For all durations of stimulation, except 1 s, a significant part of the h + w could not be explained by the energy from ATP splitting and the creatine kinase reaction. The existence of an unexplained part of the h + w confirms earlier findings. Based on its time course the h + w was divided into the stable part and the labile part. The energy from the observed chemical reactions was always sufficient to account for the stable part of the h + w. Early in the tetanus the unexplained energy is less than the labile part of the h + w. At the end of a 15 s tetanus the total amounts of unexplained energy and labile h + w are equal. It is probable that there is a close relationship between them.