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An Irreversible Thermodynamic Analysis of the Energy Conversion Process in an Active Muscle.

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Final technical rept. Apr 69-Apr 71,

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A theory of muscle contraction was developed by the application of irreversible thermodynamics to the analysis of the energy conversion process in active muscle. Individual cross-bridges, considered as subunits, are viewed as linear energy converters with constant transport coefficients. With this view of the subunits, nonlinear phenomenological equations applicable to the whole muscle in steady-state operation were obtained. The transport coefficients for the whole muscle were shown to be a function of a single parameter, n, the number of activated cross-bridges at any instant. The theory was extended to include length variations derived from the sliding filament theory and both the chemical rate and velocity are derived as functions of length and load. Alternately, the chemical rate and mechanical load are derived as functions of length and velocity. The theory was compared to mechanical data with excellent results, to heat data via the first law with fair results, and to chemical data by integrating with respect to length with good results. The variation of n with velocity was determined by two methods the first was based on experimental evidence in the form of Hills force-velocity relation, the second was based on a molecular approach. The effect of Ca on n was determined by considering the Ca-troponin system to be a system in chemical equilibrium. A model for extending the theory to cover transient phenomena is presented and finally some considerations of the process by which the muscle machinery is able to convert chemical energy directly into mechanical work are presented. Author

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  • Anatomy and Physiology

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