Synaptic localization of a 66-kDa soluble protein from skeletal muscle: evidence for its developmental and neural...

Soluble proteins from normal, adult denervated, and developing rat muscles were studied in order to identify common molecular species undergoing developmental regulation and nerve dependence. Significant increases in 66- and 30-kDa proteins were found as a consequence of 14 days of denervation. Subsequent reinnervation restores normal adult levels. During development, high levels of the 66-kDa protein were found in neonatal muscles but slowly decreased concomitant with the following postnatal maturation period; the adult levels were reached at Postnatal Day (P) 21. From the immunocytochemical studies it is deduced that both proteins were concentrated mainly at the end-plate region in adult normal muscle. Following denervation, the proteins were found distributed over the entire cell. For the 66-kDa protein, a similar pattern of extensive distribution was seen in immature muscle. Although no data for functional implications for these proteins are available at present, the properties described here make them of interest in understanding nerve-muscle interactions.