Conduction velocities in single fibers of diseased human muscle

Focal sarcolemmal lesions, segmental degeneration, and fiber splitting are observed in Duchenne muscular dystrophy and have been proposed to be major contributory causes of dysfunction of this disease. The presence of these abnormalities should affect impulse conduction along the sarcolemma. To test this prediction, we measured conduction velocities of the action potential in normal and diseased human intercostal muscle fibers by means of intracellular microelectrodes. The resting potentials of fibers from patients with Duchenne dystrophy, Becker dystrophy, and motor neuron disease were partially depolarized, and conduction velocities in these fibers were slower than normal. When the membrane potential was artifically hyperpolarized, the conduction velocity in Becker dystrophy fibers was not significantly different from normal. However, conduction velocity values in Duchenne dystrophy or motor neuron disease fibers were significantly lower than normal regardless of the level of membrane hyperpolarization. These data are analyzed in light of the presence of morphologic lesions in the diseased muscle fibers.