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Open AccessArticle

X-ray Diffraction Studies on the Structural Origin of Dynamic Tension Recovery Following Ramp-Shaped Releases in High-Ca Rigor Muscle Fibers

1
Department of Physioloogy, Teikyo University School of Medicine, Tokyo 173-8605, Japan
2
Department of Molecular Physiology, Jikei University School of Medicine, Tokyo 105-0003, Japan
3
Department of Sports Medicine, Teikyo Heisei University, Chibaken 290-0193, Japan
4
SPring-8, Hyogoken 675-5198, Japan
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2020, 21(4), 1244; https://doi.org/10.3390/ijms21041244
Received: 17 January 2020 / Revised: 1 February 2020 / Accepted: 9 February 2020 / Published: 13 February 2020
(This article belongs to the Special Issue Motile Function of Myosins in Cells and Tissues)
It is generally believed that during muscle contraction, myosin heads (M) extending from myosin filament attaches to actin filaments (A) to perform power stroke, associated with the reaction, A-M-ADP-Pi → A-M + ADP + Pi, so that myosin heads pass through the state of A-M, i.e., rigor A-M complex. We have, however, recently found that: (1) an antibody to myosin head, completely covering actin-binding sites in myosin head, has no effect on Ca2+-activated tension in skinned muscle fibers; (2) skinned fibers exhibit distinct tension recovery following ramp-shaped releases (amplitude, 0.5% of Lo; complete in 5 ms); and (3) EDTA, chelating Mg ions, eliminate the tension recovery in low-Ca rigor fibers but not in high-Ca rigor fibers. These results suggest that A-M-ADP myosin heads in high-Ca rigor fibers have dynamic properties to produce the tension recovery following ramp-shaped releases, and that myosin heads do not pass through rigor A-M complex configuration during muscle contraction. To obtain information about the structural changes in A-M-ADP myosin heads during the tension recovery, we performed X-ray diffraction studies on high-Ca rigor skinned fibers subjected to ramp-shaped releases. X-ray diffraction patterns of the fibers were recorded before and after application of ramp-shaped releases. The results obtained indicate that during the initial drop in rigor tension coincident with the applied release, rigor myosin heads take up applied displacement by tilting from oblique to perpendicular configuration to myofilaments, and after the release myosin heads appear to rotate around the helical structure of actin filaments to produce the tension recovery. View Full-Text
Keywords: muscle contraction; rigor muscle fiber; myosin head tilting; X-ray diffraction; myofilament lattice muscle contraction; rigor muscle fiber; myosin head tilting; X-ray diffraction; myofilament lattice
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Sugi, H.; Yamaguchi, M.; Ohno, T.; Okuyama, H.; Yagi, N. X-ray Diffraction Studies on the Structural Origin of Dynamic Tension Recovery Following Ramp-Shaped Releases in High-Ca Rigor Muscle Fibers. Int. J. Mol. Sci. 2020, 21, 1244.

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