[Effect of stretching muscle fibers on the conformation of F-actin].

By means of polarized UV fluorescent microscopy the conformational changes of F-actin of "ghost" glycerinated muscle fibers during the stretching 30 per cent of the resting length was found. It was observed that F-actin of the stretched fibre responds by more marked changes in their structure to ATP, glutaraldehyde and glycerin as compared to F-actin of the unstretched fibre. It was assumed that the fibre stretching changes the spatial characteristics of actin helix and increases the rigidity of thin filaments. The changes of F-actin conformation seems to play an important role in the regulation of tension level which is developed by each cross-bridge.