STRUCTURAL CHANGES OF CROSS-BRIDGES ON TRANSITION FROM ISOMETRIC TO SHORTENING STATE IN FROG SKELETAL MUSCLE

¹ JASRI, SPring-8
² Spring 8-JASRI

^* To whom correspondence should be addressed. E-mail: yagi{at}spring8.or.jp.

Submitted on April 20, 2006
Revised on June 1, 2006
Accepted on 23 August 2006

	Abstract

Structural changes in the myosin cross-bridges were studied by small-angle x-ray diffraction at a time resolution of 0.53 msec. A frog sartorius muscle, which was electrically stimulated to induce isometric contraction, was released by about 1 % in 1 ms, and then its length was decreased to allow steady shortening with tension of about 30 % of the isometric level. Intensity of all reflections reached a constant level in 5-8 msec. Intensity of the 7.2-nm meridional reflection and the (1,0) sampling spot of the 14.5-nm layer line increased after the initial release but returned to the isometric level during steady shortening. The 21.5-nm meridional reflection showed fast and slow components of intensity increase. The intensity of the 10.3-nm layer line, which arises from myosin heads attached to actin, decreased to a steady level in 2 msec, while other reflections took longer, 5-20 msec. The results show that myosin heads adapt quickly to an altered level of tension and there is a distinct structural state just after a quick release.

Key Words: cross-bridges, muscle contraction, skeletal muscle, synchrotron radiation, x-ray diffraction

This article has been cited by other articles:

				N. A. Koubassova, S. Y. Bershitsky, M. A. Ferenczi, and A. K. Tsaturyan Direct Modeling of X-Ray Diffraction Pattern from Contracting Skeletal Muscle Biophys. J., September 15, 2008; 95(6): 2880 - 2894. [Abstract] [Full Text] [PDF]