The sequential replacement of myosin subunit isoforms during muscle type transformation induced by long term electrical stimulation.

Fiber type transformation was induced in fast skeletal muscles of the rabbit by chronic electrical stimulation of the motor nerve. The accompanying changes in myosin subunit composition were examined in order to establish the precise sequence of events during this transition. Replacement of the fast by the slow isoforms of the individual light and heavy chains of the native myosin did not occur synchronously. The resultant changes in the stoichiometry of the different classes of light chains are described in relation to possible mechanisms regulating the expression of the corresponding genes. The neonatal form of myosin could not be detected at any stage of transformation, suggesting that the changes in myosin synthesis do not recapitulate the developmental sequence.