title: An x-ray diffraction study on early structural changes in skeletal muscle contraction.
abstract: Structural changes in frog skeletal muscle were studied using x-ray diffraction with a time resolution of 0.53-1.02 ms after a single electrical stimulus at 8 degrees C. Tension began to drop at 6 ms (latency relaxation), reached a minimum at 8 ms, and then twitch tension developed. The intensity of the meridional reflection at 1/38.5 nm(-1), from troponin molecules on the thin filament, began to increase at 4-5 ms and reached a maximum at approximately 12 ms. The meridional reflections based on the myosin 43-nm repeat began to decrease when the tension began to develop. The peak position of the third-order myosin meridional reflection began to shift toward the higher angle at approximately 5 ms, reached a maximum shift (0.02%) at 10 ms, and then moved toward the lower angle. The intensity of the second actin layer line at 1/18 nm(-1) in the axial direction, which was measured at 12 degrees C, began to rise at 5 ms, whereas the latency relaxation started at 3.5 ms. These results suggest that 1), the Ca(2+)-induced structural changes in the thin filament and a structural change in the thick filament have already taken place during latency relaxation; and 2), the Ca(2+) regulation of the thin filament is highly cooperative.
authors.affiliation: Japan Synchrotron Radiation Research Institute, SPring-8, Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan. yagi@spring8.or.jp
authors.forename: Naoto
authors.initials: N
authors.lastname: Yagi
mesh_terms: D000199:Actins / Q000737:chemistry / Q000502:physiology; D000818:Animals; D002352:Carrier Proteins; D004558:Electric Stimulation; D006614:Hindlimb; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology*; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000502:physiology; D009038:Motion; D009124:Muscle Proteins / Q000737:chemistry / Q000502:physiology; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000502:physiology; D009218:Myosins / Q000737:chemistry* / Q000502:physiology; D011487:Protein Conformation; D011892:Rana catesbeiana / Q000502:physiology; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical; D013329:Structure-Activity Relationship; D013696:Temperature; D014336:Troponin / Q000737:chemistry* / Q000502:physiology; D014961:X-Ray Diffraction / Q000379:methods*; D000099163:Myosin Binding Protein C
chemical_list: D000199:Actins; D002352:Carrier Proteins; D020409:Molecular Motor Proteins; D009124:Muscle Proteins; D009218:Myosins; D014336:Troponin; D000099163:Myosin Binding Protein C