Electrophysiology of Duchenne dystrophy myotubes in tissue culture

Single myotubes from cultures of 6 patients with Duchenne muscular dystrophy and 6 patients whose biopsy specimens lacked histological abnormality were studied with intracellular physiological recording. Average resting membrane potentials were 47.8 +/- 2.3 mV and 47.0 +/- 1.5 mV for the control and Duchenne cultures, respectively. Action potentials elicited at a standard resting potential of -80 mV were 97.3 +/- 4.0 mV and 98.6 +/- 8.2 mV for the two groups. Maximum rate of rise of action potentials was 154.2 +/- 25.2 V/sec for control and 143.1 +/- 37.1 V/sec for Duchenne myotubes. Action potentials mediated by an influx of calcium ions were seen only when the myotubes from both groups were bathed in high concentrations of calcium and 4-aminopyridine (20 mM and 1 mM, respectively). Thus, the plasma membrane of Duchenne dystrophy myotubes does not have active electrical properties that differ from those in controls. Previous reports of low resting membrane potentials in biopsies studied acutely may reflect secondary changes in degenerating fibers.