What do we learn by studying the temperature effect on isometric tension and tension transients in mammalian striated muscle fibres?

The significance of transient analysis of isometric tension and its temperature dependence on the molecular mechanisms of contraction is reviewed. The kinetic analysis of tension transient is essential to establish the elementary steps of the cross-bridge cycle. The temperature study is essential to deduce thermodynamic parameters of the force generation step, from which surface area changes associated with hydrophobic interaction and ionic interaction can be calculated. Experimental evidence suggests that a large scale hydrophobic and stereospecific interaction takes place at the time of force generation. This interaction is promoted by regulatory proteins troponin and tropomyosin, which is the basis for endothermic force generation. The six state cross-bridge model with two apparent rate constants is capable of explaining the temperature dependence of isometric tension and tension transients induced by temperature jump experiments. This model was previously proposed to account for the tension transients induced by sinusoidal length changes [Kawai and Halvorson (1991) Biophys J 59: 329-342]. The series compliance model is suitable for explaining the temperature effect on the stiffness data as the function of temperature, leading to the conclusion that the series compliance accounts for 40 +/- 5% of the total compliance in activated psoas fibres at 20degreesC. These results are consistent with the hypothesis that tension per cross-bridge remains the same at different temperatures, and that it is the population shift that gives rise to the characteristic temperature effect on isometric tension.