[Differentiational profiles of skeletal muscle internal membrane systems directly related to excitation-contraction...

The arrangements of internal membrane systems (transverse (T) tubules, sarcoplasmic reticulum (SR) and T-SR junction (triad)) are matched to contractile profiles in adult muscle fibers. The developmental profiles of the these internal membrane systems directly related to the excitation-contraction (EC) coupling were investigated in the chicken anterior (ALD, slow) and posterior (PLD, fast) latissimus dorsi muscles in ovo (14 to 21 days incubation: E 14-E 21) and after hatching (1 to 30 days after hatching: D 1-D 30). These internal membrane systems were visualized using confocal and electron microscopes. ALD and PLD have similar contraction time in early developmental stage (E 14-E 16), however, PLD suddenly becomes faster at E 17-E 18. Following the differentiation of faster contraction properties (E 18-E 19), density of triads increased significantly in PLD. Early development of T-tubules, on the other hand, is quite similar in both ALD and PLD. Peripherally located, longitudinally oriented T tubules, and the first T networks crossing the fiber center appear earlier in ALD (E 14-E 16) than PLD, but have similar dispositions. The final fiber type specific disposition of T-tubules is established after hatching, and three major components of the E-C coupling pathway are in place as soon as myofibrils develop.