title: Direct demonstration of the cross-bridge recovery stroke in muscle thick filaments in aqueous solution by using the hydration chamber.
abstract: Despite >50 years of research work since the discovery of sliding filament mechanism in muscle contraction, structural details of the coupling of cyclic cross-bridge movement to ATP hydrolysis are not yet fully understood. An example would be whether lever arm tilting on the myosin filament backbone will occur in the absence of actin. The most direct way to elucidate such movement is to record ATP-induced cross-bridge movement in hydrated thick filaments. Using the hydration chamber, with which biological specimens can be kept in an aqueous environment in an electron microscope, we have succeeded in recording ATP-induced cross-bridge movement in hydrated thick filaments consisting of rabbit skeletal muscle myosin, with gold position markers attached to the cross-bridges. The position of individual cross-bridges did not change appreciably with time in the absence of ATP, indicating stability of time-averaged cross-bridge mean position. On application of ATP, individual cross-bridges moved nearly parallel to the filament long axis. The amplitude of the ATP-induced cross-bridge movement showed a peak at 5-7.5 nm. At both sides of the filament bare region, across which the cross-bridge polarity was reversed, the cross-bridges were found to move away from, but not toward, the bare region. Application of ADP produced no appreciable cross-bridge movement. Because ATP reacts rapidly with the cross-bridges (M) to form complex (M x ADP x Pi) with an average lifetime >10 s, the observed cross-bridge movement is associated with reaction, M + ATP --> M x ADP x Pi. The cross-bridges were observed to return to their initial position after exhaustion of ATP. These results constitute direct demonstration of the cross-bridge recovery stroke.
authors.affiliation: Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173-8605, Japan. sugi@kyf.biglobe.ne.jp
authors.forename: Haruo
authors.initials: H
authors.lastname: Sugi
authors.forename: Hiroki
authors.initials: H
authors.lastname: Minoda
authors.forename: Yuhri
authors.initials: Y
authors.lastname: Inayoshi
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Yumoto
authors.forename: Takuya
authors.initials: T
authors.lastname: Miyakawa
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Miyauchi
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanokura
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Akimoto
authors.forename: Takakazu
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Shigeru
authors.initials: S
authors.lastname: Chaen
authors.forename: Seiryo
authors.initials: S
authors.lastname: Sugiura
mesh_terms: D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology / Q000648:ultrastructure*; D009218:Myosins / Q000378:metabolism* / Q000502:physiology; D011817:Rabbits
chemical_list: D000199:Actins; D000255:Adenosine Triphosphate; D009218:Myosins