T-system formation in cultured rat skeletal tissue.
By using a lanthanum-staining technique which enhances the visualization of the plasma membrane and its derivatives we have studied the formation of the T system in rat muscle cells differentiating in vitro. We have found that: (1) T-system formation normally occurs after myoblast fusion and is especially extensive in mature myotubes; myoblasts grown in calcium-deficient medium to prevent fusion show increased number of sarcolemmal caveolae but rare, short T tubules. (2) T-system formation in vitro differs from that displayed by rat muscle cells in vivo in that it precedes and is independent of junctional SR differentiation; the uncoordinated development of T tubules and junctional SR in vitro leads to the formation of 'inverted' triads and labyrinthine T-system networks. (3) Coated vesicles are frequently found either free in the cytoplasm or associated with growing T tubules in rat muscle cells differentiating in vitro. A role of coated vesicles in T-system formation is proposed.
D002454:Cell Differentiation; D002459:Cell Fusion; D002462:Cell Membrane / Q000648:ultrastructure; D002478:Cells, Cultured; D009132:Muscles / Q000648:ultrastructure*; D009210:Myofibrils / Q000648:ultrastructure; D009940:Organoids / Q000648:ultrastructure; D012508:Sarcolemma / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure