Distribution of connectin (titin), nebulin and alpha-actinin at myotendinous junctions of chicken pectoralis muscles: an immunofluorescence and immunoelectron microscopic study.

The distribution of connectin (titin), nebulin and alpha-actinin in the areas of myotendinous junctions of chicken pectoralis muscles was examined by immunocytochemical methods. Staining with antibodies against connectin (4C9, SM1 and P1200) and nebulin formed 'doublets' flanking nonterminal Z-bands; near the end of muscle fibres 'singlets' were seen within the terminal sarcomere on the side adjacent to the terminal Z-bands. The apical regions of muscle processes, where no myosin filaments are present although actin filaments exist, were reactive with anti-nebulin but not with anti-connectin. Antibodies against pectoralis (skeletal muscle type) alpha-actinin stained non terminal Z-bands and that against gizzard (smooth muscle type) the sarcolemma. Terminal Z-bands were unreactive with both of these antibodies. These findings indicate that, although terminal and nonterminal Z-bands differ in their molecular composition, connectin and nebulin filaments appear to link myosin and actin filaments, respectively, to both Z-band types.