[Immediate sources of energy in muscle contraction].
(1972) Journal de Physiologie — Vol. 65, p. Suppl 1:5A-50 (1972)
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- Authors
Maréchal, Georges 
- Abstract
- At the end of this study what can we conclude? Classical theory accounts for most of the facts. Overall, the energy (heat and work) provided by a muscle is accompanied by a hydrolysis of phosphorylcreatine (PC). The apparent enthalpy of this reaction is - 9 to - 11 kcal / mole. The production of work accelerates the consumption of PC, and therefore does not require the intervention of another chemical reaction; stretching the muscle slows PC hydrolysis, although the force muscle is greatly increased. This hydrolysis of phosphorylcreatine has the meaning of a restoration reaction: it is the result of two successive reactions. The first is the hydrolysis of ATP to ADP on contact with contractile proteins: this is the reaction of the chemical-mechanical coupling; the second is rephosphorylation of ADP to ATP at the expense of phosphorylcreatine. After contraction, creatine is rephosphorylated (via the ATP-ADP system) by glycolysis and oxidations. This theory is however incomplete, but one can currently only point out its shortcomings, without being able to replace it with a new, more coherent theory. Let us summarize the main points of disagreement: a) PC's debt. The first twitches in a series or the start of a tetanus are accompanied by lower hydrolysis of PC than expected; on the other hand, there is a post-contractile hydrolysis of PC, which, probably, betrays the “payment” of the debt contracted at the beginning of the contractile activity. Debt is not a hydrolysis of ATP. b) The transient increase in ATP levels at the start of tetanus cannot be explained by the chemical reactions described in classical theory. c) The very high heat production during an isometric tetanus at 20°C far exceeds that produced by the hydrolysis of ATP and PC, glycolysis and oxidations. d) Even as regards the contractions where PC accounts for the energy produced by the muscle, there remains a disagreement between various experimenters: some find that the enthalpy of PC hydrolysis in muscle is -9 kcal / mole: others estimate it at -11 kcal / mole, or even -13 kcal / mole.
Citations
Maréchal, G. (1972). [Immediate sources of energy in muscle contraction]. Journal de Physiologie, 65, Suppl 1:5A-50. https://hdl.handle.net/2078.5/214195 (Original work published 1972)