The ends of muscle fibers form many longitudinal projections which are further divided into numerous processes and attach to the collagen fibrils of tendons to form myotendinous junctions (MTJs). Immunocytochemical and electron microscopic observations on pectoralis muscles of the chicken revealed the presence of an elastic filamentous protein, connectin (titin), within the terminal sarcomere on the side adjacent to the terminal Z bands, and the absence of connectin and myosin and the presence of actin at the apical sarcoplasmic region of MTJ processes between the terminal Z band and the MTJ sarcolemma. Intermediate voltage electron microscopy showed that T tubules in the terminal sarcomere were absent at the level of the A-I junction on the MTJ side in the rat vastus intermedius, and at the level of the terminal Z band or under the MTJ subsarcolemmal densities in the chicken pectoralis.
Shimada, Y.; Atsuta, F.; Sonoda, M.; Shiozaki, M.; and Maruyama, K.
"Distribution of Connectin (Titin) and Transverse Tubules at Myotendinous Junctions,"
Scanning Microscopy: Vol. 7
, Article 17.
Available at: https://digitalcommons.usu.edu/microscopy/vol7/iss1/17