Size and shape of transverse tubule openings in frog twitch muscle fibers.
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.
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