Quantitative ultrastructural changes in satellite cells of rats immobilized after soleus muscle denervation

Quantitative ultrastructural evaluation of satellite cells (SCs) of rats immobilized for 7, 14, and 36 days after soleus muscle denervation was performed. Alterations in SCs of experimental animals concerned mainly the decrease in the size of cells and their nuclei, in the volume fractions of the nucleus and nucleolus, as well as in the number of ribosome-like structures. They suggest that immobilization which proceeded denervation caused a decline in cell activity. An increase in the volume fraction and number of endosome/lysosome-like structures, suggesting elevated processes of degradation was also observed. The changes occurred mainly in the period between 7 and 14 days after muscle denervation and immobilization. In all groups of experimental animals an increase in number of caveolae-like structures on both, inner (muscle fiber-facing) and outer (basal lamina-facing) sides of SCs was found. Thus, it is likely that SCs of denervated and immobilized rats are affected by signal molecules released by muscle fibers and/or other cell types present in muscle. A tendency in changes in SCs, observed in the present study, was similar to those which we noticed previously in denervated soleus muscle. However, immobilization after denervation aggravated some of the ultrastructural alterations or the changes appeared earlier.