Caffeine contractures in denervated slow-twitch and fast-twitch muscles of the rat.

Caffeine contractures (25 mM) and twitches were registered in vitro (34 degrees C) in normal and denervated soleus and extensor digitorum longus of the rat. Both muscles lost weight progressively after denervation although the loss of weight in soleus muscles was more manifest. Denervated extensor digitorum longus muscles showed an increase in the caffeine contracture tension (expressed in g/g muscle) whereas the response generated by denervated soleus muscles was smaller than the control values. The time to peak of the caffeine responses was shortened in both types of muscles after denervation. Twitches were larger and had a slower time course than in normal muscles, especially in the extensor digitorum longus muscles. These findings suggest that some changes in the excitation-contraction coupling could be responsible for the potentiation of the twitches in denervated muscles.