title: Sarcomere-length dependence of lattice volume and radial mass transfer of myosin cross-bridges in rat papillary muscle.
abstract: We examined the sarcomere length-dependence of the spacing of the hexagonal lattice of the myofilaments and the mass transfer of myosin cross-bridges during contraction of right ventricular papillary muscle of the rat. The lattice spacing and mass transfer were measured by using X-ray diffraction, and the sarcomere length was monitored by laser diffraction at the same time. Although the lattice spacing and the sarcomere length were inversely related, their relationship was not exactly isovolumic. The cell volume decreased by about 15% when the sarcomere length was shortened from 2.3 micro m to 1.8 micro m. Twitch tension increased with sarcomere length (the Frank-Starling law). At the peak tension, the ratio of the intensity of the (1,0) equatorial reflection to that of the (1,1) reflection was smaller when the tension was greater, showing that the larger tension at a longer sarcomere length accompanies a larger amount of mass transfer of cross-bridges from the thick to the thin filament. The result suggests that the Frank-Starling law is due to an increase in the number of myosin heads attached to actin, not in the average force produced by each head.
authors.affiliation: SPring-8/JASRI, 1-1-1 Kouto, Mikazuki, Sayo, 679-5198, Hyogo, Japan. yagi@spring8.or.jp
authors.forename: Naoto
authors.initials: N
authors.lastname: Yagi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Okuyama
authors.forename: Hiroko
authors.initials: H
authors.lastname: Toyota
authors.forename: Junichi
authors.initials: J
authors.lastname: Araki
authors.forename: Juichiro
authors.initials: J
authors.lastname: Shimizu
authors.forename: Gentaro
authors.initials: G
authors.lastname: Iribe
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Nakamura
authors.forename: Satoshi
authors.initials: S
authors.lastname: Mohri
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Tsujioka
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Suga
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Kajiya
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D018613:Microscopy, Confocal; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000648:ultrastructure*; D009218:Myosins / Q000502:physiology*; D010210:Papillary Muscles / Q000502:physiology / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D012518:Sarcomeres / Q000502:physiology* / Q000648:ultrastructure*; D014961:X-Ray Diffraction
chemical_list: D009218:Myosins