[High time resolution x-ray study of the dynamics of a single muscle contraction]

A method of the diffraction cinema which enables to study the time-course of structural changes during twitch contraction is described. The method is based on using synchrotron radiation, position-sensitive counter and small-angle focusing X-ray camera. Only 0.1 s is required to record a good muscle X-ray diagram: meridional diagram contains all layer-lines beginning with the 429 A; the equatorial diagram contains 5 reflections including very weak alpha-reflection. The method allows to record 64 sequent diffraction patterns with different duration (1--2000 ms). The experiment is handled by a computer. Some tens of the films of isometric twitch contraction with time resolution of 3--20 ms have been obtained. During isometric contraction considerable changes in the intensity of both meridional and equatorial reflections were found. The changes were interpreted as indicating movement of cross-bridges toward the thin filaments. During the latent phase there are no visible changes in the intensity of the reflections; the result indicates that during this phase there are no structural changes in position and configuration of cross-bridges.