PARALYSIS OF RAT SKELETAL-MUSCLE EQUALLY AFFECTS CONTRACTILE PROPERTIES AS DOES PERMANENT DENERVATION

The effects of long lasting (4-5 weeks) nerve conduction block and den ervation were compared by investigating contractile, morphological and histochemical properties of slow (soleus) and fast (EDL) rat skeletal muscles. The block was based on improved perfusion techniques of the sciatic nerve with a tetrodotoxin (TTX) solution delivered at doses ad equate to obtain maximal effects in the muscles. The TTX-inactivated a xons retained normal histological and physiological properties such as the ability to evoke full contractile responses, to regenerate, and t o completely reinnervate muscle. In spite of their intact innervation or of their full reinnervation, the TTX-paralysed muscles underwent we ight loss, fibre atrophy and reduction in force output quantitatively indistinguishable from those following denervation. The same was true for all other contractile parameters tested, that is, twitch speed, tw itch to tetanus ratio, post-tetanic potentiation, endurance, and fibre type composition. The results indicate the fundamental role of activi ty as a regulatory signal for muscle contractile properties, while the y do not support the notion of a participation of chemical, activity-i ndependent factors in this regulation.