Electrophysiologic differences between normal and dystrophic avian muscle.

In the avian model of muscular dystrophy, electrophysiologic studies have shown alterations in the action potential characteristics of dystrophic muscle in vitro, supporting the notion that a membrane defect exists in avian dystrophy. As neurogenic and vascular etiologies have also been proposed, we examined the characteristics of action potentials recorded in a novel in vivo preparation of the extensor digitorum communis muscle in 8-week-old normal and dystrophic chickens. To facilitate intracellular recording, dantrolene sodium was used to attenuate the muscle twitch. Results showed that although the resting membrane potential, action potential amplitude and the action potential maximum rate of rise were similar in normal and dystrophic cells, the action potential duration at half the maximum amplitude was increased in dystrophic cells. This observation has not been previously reported for dystrophic avian muscle and suggests that a defect in the sarcolemmal potassium conductance is an early change in dystrophic avian muscle.