Nerve crush induced changes in molecular forms of acetylcholinesterase in soleus and extensor digitorum muscles

The molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) extracted from the fast twitch extensor digitorum longus (EDL) and slow twitch soleus (SOL) muscles, were separated by velocity sedimentation after sciatic nerve crush. Three molecular forms were routinely separated from EDL and four from SOL muscle. In the EDL, the 4S and 10S represented the greatest amounts of AChE, and in the SOL the 12S and 16S were the major constituent forms of the enzyme. Total AChE activity in EDL and SOL muscles rapidly decreased after nerve crush. During reinnervation (2 weeks postcrush), total AChE activity in the EDL gradually recovered, whereas the SOL exhibited a 2.5-fold transient increase above control. Immediately after denervation, decreases in the three AChE forms from the EDL (4, 10, and 16S) were evident, whereas the SOL exhibited both rapid increases (4 and 10S) and decreases (12S and 16S). In both muscles the 4S form reappeared before the 16S and 10S molecular forms, suggesting that the light form, 4S, may be a precursor of the heavier molecules. Transient increases during reinnervation occurred in the 16S AChE form in both muscles; however, they were approximately five times greater in the SOL than in the EDL. In the SOL all other molecular forms showed similar increases, whereas none was seen in the EDL. Possible mechanisms are differences in synthesis and catabolism, and in release of molecular forms from these muscles.