Effects of temperature on tension, tension‐dependent heat, and activation heat in twitches of frog skeletal muscle.

Abstract

The effects of temperature on muscle energy liberation (heat plus work production) and isometric twitch force production were measured at rest length (l0) and at long muscle lengths (.apprx. 1.35 l0) where twitch force was greatly depressed. Force production and energy liberation at l0 declined progressively as muscle temperature was elevated from 0.degree. to 20.degree. C. Force production decreased to a greater extent than did energy liberation. A plot of energy liberation vs. twitch force suggested that a fraction of the l0 energy liberation was produced independently of temperature. The energy liberated at long muscle lengths, the activation heat, was independently of muscle temperature. The activation heat is interpreted as reflecting the energy dissipated during Ca2+ cycling and suggests that, under the conditions of these experiments, the amount of Ca2+ released with stimulation is independent of muscle temperature and subsequent muscle force production. Skeletal muscle energy liberation is dependent on muscle force production and the energy liberation associated with Ca2+ cycling is essentially independent of muscle length in the range l0-1.35 l0.