Reloading of atrophied rat soleus muscle induces tenascin-C expression around damaged muscle fibers.

The hypothesis was tested that mechanical loading, induced by hindlimb suspension and subsequent reloading, affects expression of the basement membrane components tenascin-C and fibronectin in the belly portion of rat soleus muscle. One day of reloading, but not the previous 14 days of hindlimb suspension, led to ectopic accumulation of tenascin-C and an increase of fibronectin in the endomysium of a proportion (8 and 15%) of muscle fibers. Large increases of tenascin-C (40-fold) and fibronectin (7-fold) mRNA within 1 day of reloading indicates the involvement of pretranslational mechanisms in tenascin-C and fibronectin accumulation. The endomysial accumulation of tenascin-C was maintained up to 14 days of reloading and was strongly associated with centrally nucleated fibers. The observations demonstrate that an unaccustomed increase of rat soleus muscle loading causes modification of the basement membrane of damaged muscle fibers through ectopic endomysial expression of tenascin-C.