THE CHANGES IN THE STRUCTURAL ORGANIZATIO N OF RECONSTITUTED FILAMENTS OF MYOSIN FROM SKELETAL-MUSCLES OF HIBERNATING GROUND-SQUIRRELS CITELLUS-UNDULATUS DURING AROUSING

Electron microscopic observations of myosins, isolated from skeletal m uscles of ground squirrels at the different states (hybernation - M(hy b); winter activity - M(act); the beginning of arousal - M(begin); the end of arousal - M(end)) have revealed the differences in the structu re of their filaments. The filaments reconstituted from M(hyb), M(act) and M(end) (rectal temperature 27 degrees C) exhibit the ordered stru cture with the myosin heads arranged regularly (period of 14,3 nm) on the filament surface. The filaments of M(begin) (rectal temperature 12 degrees C) have irregular structure with random arrangement of the my osin head clusters alternating with regions of different length devoid of heads. To elucidate the molecular bases of the structural differen ces observed by us the solubility of the above myosins, the paracrysta l structure of corresponding light meromyosins as well as the composit ion and state of myosin light chains have been studied. M(begin) appea red to have the greatest solubility in comparison with the other ones. This points to the possible changes in myosin heavy chains during hyb ernation and arousal although no differences have been revealed in par acrystals of light meromyosins. The amount of light chains (LC3) decre ased up to 40% in M(hyb) in comparison with M(act) and then increased up to 60-70% in M(begin) within 1-1,5 hours of arousal. It is supposed that the rapid changes in isoforms of heavy and light chains in M(beg in) lead to disturbance of regular mode of filament assembly in vitro, and can result In the lowering of muscle contraction efficiency and i n the increasing of the heat release. The later can contribute to ther mogenesis of the animal during arousal.