Chronic denervation of rat diaphragm: selective maintenance of adult fast myosin heavy chains.

After long-term denervation in mixed rat muscles there is a selective loss of slow myosin. The bidimensional electrophoretic pattern of light chains and the results of preliminary studies on heavy chains have left open the question of whether the nature of the residual fast-like myosin is of the immature or adult type. We have further investigated chronically denervated myosin by (1) electrophoresis in nondissociating conditions; (2) acidic electrophoresis of the heavy chains; and (3) proteolytic mapping of the heavy chains. These techniques clearly distinguish adult myosins from those present in immature muscles. Using these criteria, myosin from the chronically denervated diaphragm is of an adult type, even though the presence of trace amounts of embryonic myosin cannot be excluded. The contractile properties also indicate that chronically denervated hemidiaphragm is more similar to an adult fast muscle than to an immature muscle. The selective maintenance after long-term denervation of fast myosin in adult muscle provides good evidence of the independence of the genetic expression of myosin from a direct neural chemotrophic control.