A sliding filament model for skeletal muscle: dependence of isometric dynamics on temperature and sarcomere length.

Abstract The sliding filament model of A. F. Huxley is used to derive a formula for the rate constant for exponential increase of tension to the plateau value in an isometric tetanus. The formula agrees well with measured values of the rate constant for frog sartorius muscle at several temperatures when most sarcomeres have length in the range at which they develop maximum force. The comparison with data suggests that the distance over which an attached cross-bridge moves decreases markedly with increasing temperature, from about 100 A at 2°C to less than 5 A at 20°C. The relation of the analysis and its results to Hill's theory of the isometric myogram is discussed. The Huxley theory is extended to treat the rise of isometric force in a muscle fiber of such length that the number of cross bridges opposite thin filaments is less than maximum and changes with time. Predictions of the extended theory do not agree well with observed dynamics of muscle, probably because the extended theory neglects effects of inequalities in sarcomere length within the fiber.