Effects of denervation on the distribution of myosin isozymes in skeletal muscle fibers

Abstract

The pattern of distribution of myosin isozymes was examined with respect to the fiber population in the denervated rat diaphragm. Myosin was demonstrated by indirect immunofluorescence using antibodies against chicken myosin and by localization of ATPase activity. In the normal diaphragm, a heterogeneous fast-twitch muscle, the component fibers react with antibodies against fast or slow myosin, but usually not with both. By 8 weeks after removal of the nerve supply, all fibers reacted with antibodies specific for fast myosin, and many reacted with anti-slow myosin as well. This indicates either that multiple forms of myosin coexist within individual muscle fibers or that a unique myosin(s) is present which has determinants in common with both fast and slow isozymes. This pattern was observed for at least 24 weeks after denervation. At all stages, the localization of alkali-stable and acid-stable ATPase activity correlated well with the response to anti-fast and anti-slow myosin, respectively. We conclude that the normal adult neuromuscular relationship is required for the preferential distribution of fast and slow myosins into different populations of fibers. New myosin is nevertheless synthesized in the absence of the nervous system, and characteristics of both fast and slow isozymes are evident even after prolonged denervation.