Effects of actinomycin D on contractile properties of denervated rat skeletal muscle.

We studied the mechanical and electrical properties in the extensor digitorum longus muscle of Wistar rats in vitro 4 days after denervation. In a group of animals, actinomycin D was injected intravenously at the time of denervation. The prolongation of contraction and relaxation time, and the increase in twitch tension observed in denervated muscles were prevented by the drug. Other denervatory changes such as the elimination of cooling potentiation, posttetanic potentiation, staircase phenomenon, and shortening of caffeine contracture were also inhibited or partially reverted by actinomycin D. In addition, some electrical denervatory changes such as the decrease of resting membrane potential and slowing of maximum rate of fall of the action potential were partially abolished by actinomycin D. These results support the hypothesis that a new synthesis of proteins is related to denervation changes.