Abstract des Autors

Using several electrophoretic techniques, this study examined the effects of 3 weeks hindlimb suspension on the patterns of isomyosins, myosin heavy chain (HC) isoforms and myosin light chain (LC) isoforms in the soleus muscle of the rat. The suspended soleus showed a shift in the HC isoform distribution with a marked increase in fast HC isoforms and a commensurate decrease in HC-I. In addition, the change in the fast HC isoforms consisted of the expression of HC-IId and HC-IIb absent in the normal soleus. In contrast to HC isoforms, suspension did not lead to appreciable changes in LC isoform distribution. Analyses of electrophoresis under nondenaturing conditions demonstrated that the normal soleus expressing HC-I and HC-IIa isoforms contained two isomyosins. Although, of the two isomyosins observed in the normal soleus, the faster migrating band most likely represented the HC-IIa-based one (FMas), its mobility was not identical with that of the HC-IIa-based isomyosin (FMaf) found in fast-twitch muscles, migrating in the order FMaf>FMas. FMas was designated as intermediate isomyosin (IM). Some of the suspended soleus contained slow isomyosin (SM) and IM whereas the others comprised FM3 and/or FM2 as well as SM and IM. In spite of the expression of HC-IIb and HC-IId in the suspended soleus, FM3 and FM2 observed in these muscles exhibited distinct mobilities from either HC-IId-based or HC-IIb-based isomyosins comprised in fast-twitch muscles. These results suggest that some of newly expressed HC-IId and/or HC-IIb isoforms in the suspended soleus are associated with not only fast but also slow LC isoforms and function as a constitutive element of the myosin molecule. Verf.-Referat