Molecular alterations in the perijunctional region of frog skeletal muscle fibres following denervation.

The anatomical distribution of a frog skeletal muscle antigen was studied using immunofluorescence microscopy and a monoclonal antibody 3B6 that was produced against denervated skeletal muscle. In innervated muscles, the monoclonal antibody 3B6 stain was associated with the inner surface of the muscle plasma membrane at the endplate and myotendinous junction. After denervation, the monoclonal antibody 3B6 stain extended from the endplate laterally around the perimeter of muscle fibres and longitudinally well beyond the endplate for a total length of 600-1000 microns. The monoclonal antibody 3B6 stain thus forms a cylindrical structure centred on the endplate. This observation shows that denervation produces a non-homogeneous molecular change in skeletal muscle fibres: an antigen that is present in high concentrations at innervated endplates appears in restricted perijunctional regions of denervated muscle fibres. It further suggests that perijunctional regions of denervated muscle fibres differ from the remaining non-endplate regions in molecular composition and possibly also in function.