Stimulation-induced expression of slow muscle myosin in a fast muscle of the rat. Evidence of an unrestricted adaptive capacity.

Fast muscles of the rat hind limb were stimulated continuously at 10 or 20 Hz for periods of 55-61 days by means of an implantable neuromuscular stimulator. Gel electrophoresis clearly demonstrated the presence in stimulated muscles of slow myosin light and heavy chains, although fast isoforms were still present in all cases. Thus, contrary to previous reports, induction of slow myosin isoforms does occur in this, as in other, mammalian species. The time course of the response to stimulation appears to be more extended than that seen in the rabbit.