Changes produced by chronic denervation in the temperature-dependent isometric contractile characteristics of rat fast and slow twitch skeletal muscles.

1. Influence of temperature (range 20-35 degrees C) on the isometric contractile properties of normal and chronically denervated fast-twitch extensor digitorum longus and slow-twitch soleus muscles of the rat have been studied in vitro. 2. The times to peak twitch tension of denervated muscles were longer than those of normal in both types of muscle. The denervated muscles were, however, identifiable as 'fast-twitch' or 'slow-twitch' throughout the entire temperature range. 3. The twitch tension/tetanic tension ratios of the denervated muscles at 35 degrees C were significantly higher than those of the normal muscles. 4. The twitch tension of the normal extensor digitorum longus muscles increased whereas that of the normal soleus muscles decreased with cooling from 35 to 20 degrees C. Such a qualitative difference did not exist between the denervated extensor digitorum longus and soleus muscles. The twitch tensions of both denervated muscles decreased with cooling. 5. Cooling to 20 degrees C resulted in a greater fall in tetanic tension in the denervated than in the normal muscles.