[Changes in structural organization of reorganized myosin filaments from skeletal muscles of the winter-hibernating suslik Citellus undulatus during awakening].

Electron microscopic observations of myosins, isolated from skeletal muscles of ground squirrels at the different states (hybernation-Mhyb; winter activity--M(act); the beginning of arousal-M(begin); the end of arousal-M(end)) have revealed the differences in the structure of their filaments. The filaments reconstituted from Mhyb, M(act) and M(end) (rectal temperature 27 degrees C) exhibit the ordered structure 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 myosin head clusters alternating with regions of different length devoid of heads. To elucidate the molecular bases of the structural differences observed by us the solubility of the above myosins, the paracrystal structure of corresponding light meromyosins as well as the composition and state of myosin light chains have been studied. M(begin) appeared to have the greatest solubility in comparison with the other ones. This points to the possible changes in myosin heavy chains during hybernation and arousal although no differences have been revealed in paracrystals of light meromyosins. The amount of light chains (LC3) decreased up to 40% in Mhyb in comparison with Mact and then increased up to 60-70% in Mbegin within 1-1.5 hours of arousal. It is supposed that the rapid changes in isoforms of heavy and light chains in Mbegin lead to disturbance of regular mode of filament assembly in vitro, and can result in the lowering of muscle contraction efficiency and in the increasing of the heat release. The later can contribute to thermogenesis of the animal during arousal.