Effects of deafferentation on the size and myosin phenotype of muscle fibers on stretching of the rat soleus muscle in conditions of gravitational unloading.

The aim of the present work was to assess the contributions of the reflex and local components to preventing decreases in the size and changes in the ratio of fibers containing the slow and fast isoforms of myosin heavy chains during chronic stretching of a postural muscle in rats in conditions of gravitational unloading. A unilateral surgical deafferentation method was used. The results demonstrated that deafferentation of the hindlimb had no effect on preventing reductions in muscle fiber size in conditions of chronic muscle stretching in conditions of gravitational unloading. The results obtained from these experiments did not support the hypothesis that the predominant contribution to preventing the development of atrophic changes comes from activation of muscle afferents in chronic stretching of the unloaded muscle. Deafferentation of both suspended animals and those with normal motor activity led to increases in the proportion of soleus muscle fibers containing the slow isoforms of myosin heavy chain.

[Effect of deafferentation on the size and myosin phenotype of muscle fibers during stretching of rat m. soleus and gravitational unloading]. / Vliianie deafferentatsii na razmery i miozinovyi fenotip myshechnykh volokon pri rastiazhenii m.soleus krysy na fone gravitatsionnoi razgruzki.

The study was purposed to evaluate the contribution of the reflectory and local components during the chronic stretch of the postural muscle to the attenuation of the unloading-induced fiber size reduction and changes in the myosin heavy chain (MHC) profile. The surgical unilateral deafferentation (dorsal rhizotomy) was used. It was shown that unilateral deafferentation didn't influence on the amelioration of unloading-induced fiber size reduction in chronically stretched soleus muscle. Thus, the results obtained in the present study don't confirm the hypothesis, supposing the predominant contribution of the muscle afferent activation to the attenuation of unloading-induced fiber atrophy. Deafferentation of unloaded as well as control rats leads to the increase of the percentage of fibers expressing slow MYC isoforms.