title: Size and shape of transverse tubule openings in frog twitch muscle fibers.
abstract: The openings of transverse tubules in frog twitch fibers are described. The tubules open to the extracellular space by a narrow neck, with an inner diameter of 20 nm. The most peripheral portion of the tubules is tortuous and has a variable diameter. The similarity in size of the openings of T tubules and caveolae and the meandering path of the tubules are sufficient to account for the paucity of observed openings.
mesh_terms: D000818:Animals; D005110:Extracellular Space / Q000648:ultrastructure; D008854:Microscopy, Electron; D009132:Muscles / Q000294:innervation / Q000637:transplantation / Q000648:ultrastructure*; D011894:Rana pipiens / Q000033:anatomy & histology*; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure*; D014182:Transplantation, Autologous; D014630:Vagus Nerve / Q000502:physiology