title: Discrimination between fast- and slow-twitch fibres of guinea pig skeletal muscle using the relative surface density of junctional transverse tubule membrane.
abstract: The black reaction of Golgi was used to infiltrate transverse (T) tubules in fast-twitch glycolytic (FW), fast-twitch oxidative-glycolytic (FR) and slow-twitch (S) type fibres in muscles of guinea pigs. Non-junctional (fT) and junctional (jT) segments of the T-tubule network are clearly demarcated by this technique. Digitized planimetry and direct measurements were used to determine the proportion of T-tubule network forming junctions with the sarcoplasmic reticulum (%LjT) and to estimate the surface density (surface area per fibre volume) of total and junctional T membrane. From these data, the volume density (number per fibre volume) of junctional feet was calculated. All three types of fibres have approximately equal surface density of T tubules, but the FW and FR fibres have a much higher proportion of jT. The calculated volume density of feet is twice as high in fast-twitch as in slow-twitch fibres.
authors.affiliation: Department of Anatomy, University of Pennsylvania, Philadelphia.
authors.forename: C
authors.initials: C
authors.lastname: Franzini-Armstrong
authors.forename: D G
authors.initials: DG
authors.lastname: Ferguson
authors.forename: C
authors.initials: C
authors.lastname: Champ
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D005260:Female; D006168:Guinea Pigs; D008433:Mathematics; D009119:Muscle Contraction; D009132:Muscles / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D009469:Neuromuscular Junction / Q000648:ultrastructure*; D012518:Sarcomeres / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure*