[X-ray diffraction studies of muscles]

A brief account of the modern state of X-ray diffraction studies of muscles is presented. Recently many investigaters payed particular attention to concrete changes taking place in structural-executive (protofibrillar) apparatus of muscles at the change of their state. The drawback of these works is the necessity of interpreting the data on the basis of model ideas having definite variability. Our studies here presented differe by the approach to the problem and to a certain extent by the methods applied. Our main task was to study the dynamics of structural changes in muscles while the latter perform their working function. Special attention was payed to the studies of muscles at different shortening eithor on living or fixed samples. The effect of some conventional fixators on structural parameters evaluated by X-ray analysis was studied for the first time. A means of stroboscopic accumulation of X-ray diffraction patterns for periodic fast processes was developed. One of our main tasks was to find the range of applicability sliding mechanism hypothesis for describing muscle shortening. It was observed that the sliding mechanism held true for the desscription of the structure of muscles shortened in a physiological range. X-ray diffraction patterns were obtained which were different for the shortenings according to the sliding mechanism and those with A-disc shortening and during supercontraction. The limits of the sliding model were evaluated by some of these characteristics for muscle of different composition and properties. The problem of the forces realizing muscle shortening is discussed, some of the author's studies being taken into account. Muscle should be assessed as a complex heteromorph biological object and as a complex liquid crystalline system to create the models of its molecular structure and to elucidate the precise mechanism of its functional activity.