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

1. The effects of temperature on muscle energy liberation (heat plus work production) and isometric twitch force production were measured at rest length (l o) and at long muscle lengths (approx. 1.35 l o) where twitch force was greatly depressed. 2. Force production and energy liberation at l o declined progressively as muscle temperature was elevated from 0 to 20 degrees 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 l o energy liberation was produced independent of temperature. 3. The energy liberated at long muscle lengths, the activation heat, was independent of muscle temperature. The activation heat is interpreted as reflecting the energy dissipated during Ca2+ cycling and thus 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. 4. Analysis of the results also supports the conclusions that skeletal muscle energy liberation is dependent on muscle force production and that the energy liberation associated with Ca2+ cycling is essentially independent of muscle length in the range of l o--1.35 l o.