ACTIVITY OF MU-CALPAIN AND M-CALPAIN IN REGENERATING FAST AND SLOW-TWITCH SKELETAL-MUSCLES

Calpains - non-lysosomal intracellular calcium-activated neutral prote inases, form a family consisting of several distinct members. Two of t he isoenzymes: mu (calpain I) and m (calpain II) responded differently to the injury during complete regeneration of Extensor digitorum long us (EDL) muscle and partial regeneration of Soleus muscle. In the crus hed EDL the level of m-calpain on the 3rd and 7th day of regeneration was higher than in non-operated muscles, whereas the activity of this calpain in injured Soleus decreased. The level of mu-calpain in EDL os cillated irregularly during regeneration whereas in Soleus of both inj ured and contralateral muscles its level rapidly rose. Our results sup port the hypothesis that m-calpain is involved in the process of fusio n of myogenic cells whereas mu-calpain plays a significant but indirec t role in muscle regeneration.