The effect of the performance of work on total energy output and metabolism during muscular contraction

Abstract

SUIMMARY1. The production of heat (h) and work (w) and the changes in phosphocreatine (PCr) and ATP have been measured on tetanized isolated frog muscles (unpoisoned and in oxygen at 00 C) during shortening at constant velocity and during isometric contraction (both without relaxation). The former type of contraction was designed to maximize the fraction w/(h + w); the latter to minimize it.2. The duration of the isometric contraction was made considerably longer than that of the isovelocity contraction so that the (h + w) productions during the two contractions were approximately equal. 3. The PCr break-down during the working contraction was considerably greater than that during the isometric contraction.4. No detectable ATP changes occurred. 5. The break-down of PCr is sufficient to account for the work evolved: there is no reason to suppose that the work comes from an unidentified source.6. In both types of contraction extra energy is evolved that cannot be accounted for by concurrent splitting of PCr. The time course of evolution of this extra energy is similar in all types of contraction, suggesting that it may arise from a process other than cross-bridge interaction.7. The results are discussed in terms of current cross-bridge theory and muscle kinetics. The mean cycle times of a cross-bridge during working and isometric contractions are 0-12 see and 0 34 see respectively. During the working contraction cross-bridges spend about one quarter of the time attached to actin filaments.

Chemo‐mechanical energy transduction in relation to myosin isoform composition in skeletal muscle fibres of the rat

“…This is due to the fact that in this study thermodynamic efficiency (workÏfree energy) and not mechanical efficiency (workÏwork + heat) was determined and that skinned (Triton-treated) fibres, in which ATP consumption for ionic transport was minimized, were used. Determinations of thermodynamic efficiency in frog muscles (Kushmerick & Davies, 1969;Curtin, Gilbert, Kretzschmar & Wilkie, 1974) have given values around 0·4-0·5. In slow Xenopus fibres values of 0·8 have been obtained after correction of the heat production associated with calcium uptake by the sarcoplasmic reticulum (Buschman, Elzinga & Woledge, 1996).…”

Post-contractile phosphocreatine splitting in muscle as revealed by time-resolved 31P nuclear magnetic resonance.

“…To be more specific, CURTIN et al (1974) estimate the steady rate of turnover of crossbridges in an isometric contraction of frog skeletal muscle at low temperatures. The results show that the average duration of a cycle is 0.68 sec, assuming two ATPase sites are associated with each myosin molecule.…”

Investigation of Sounds Produced by Healthy and Diseased Human Muscular Contraction

“…They also cited studies (Huxley, 1974;Taylor and Lymn, 1972;Curtin et al, 1974) which indicated that the cycling of cross bridges occurs at approximately 20 Hz.…”