Physical Chemistry of Contractile Process in Muscle

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Abstract
The physicochemical model of the contractile process, discussed in a previous paper, is used to interpret the time-tension relation in an isometric tetanic contraction. The instantaneous rate of development of tension is assumed to be proportional to the instantaneous net rate of the reactions LS. Numerical values of the rate constants obtained from isotonic expts. give satisfactory agreement between exptL and theory. It is estimated that in a twitch of the frog''s sartorius at O[degree]C, approx. 15% of the contractile units are converted into the short state by the time relaxation begins. A quick stretch, producing a tension beyond a critical value, will reverse the direction of the net reaction. These ideas explain the effects of a quick stretch on the course of the time-tension curve in a twitch, reported recently by A. V. Hill. If a muscle is stretched before stimulation, a part of the contractile units is converted into an inactive form when the muscle is stimulated. This explains the peculiar length-tension curve of a muscle stretched before stimulation. A complete interpretation of the Blix length-tension diagram is given.

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