Effect of temperature on mechanical and myothermic properties of rabbit smooth muscle.

The mechanical performance and the heat production of 18 rabbit rectococcygeus muscles have been measured at 19 degrees C and 29 degrees C. The rate of energy liberation in a tetanus was 2.96 +/- 0.14 mW/g at 19 degrees C and 5.84 +/- 0.25 mW/g at 29 degrees C. At both temperatures there was a linear relationship between total (initial + recovery) heat production and the stress-time integral for stimulus durations up to 13 s. The slope of the relationship had a Q10 of 1.8. Recovery heat evolution, measured after mechanical relaxation was complete, was approximately exponential in character. The final time constant for recovery heat liberation was 63.1 +/- 5.5 s at 19 degrees C and 32.3 +/- 2.4 s at 29 degrees C. After-loaded isotonic force-velocity data were fitted with the hyperbolic version of Hill's characteristic equation (A. V. Hill. Trails and Trials in Physiology. London: Arnold, 1965). The a/Po ratio was practically temperature independent, but maximal shortening velocity and the constant b had Q10's of 2.5 and 2.7, respectively.