Stimulation of denervated rat soleus muscle with fast and slow activity patterns induces different expression of...

The relative amount and distribution of acetylcholinesterase (AChE) molecular forms were studied in slow soleus and (less extensively) in fast extensor digitorum longus (EDL) muscles of the rat before and after denervation and direct stimulation. Normal EDL muscles showed higher total and specific AChE activity than normal soleus muscles and contained essentially three different molecular AChE forms (G1, G4, and A12) as opposed to six forms (G1, G2, G4, A4, A8, and A12) in the soleus. Denervation reduced AChE activity in both muscles. In the soleus direct stimulation starting 2 to 3 weeks after denervation increased the specific AChE activity markedly. The increase started 12 to 24 hr after the onset of stimulation, reached 3 to 5 times normal values after 2 to 7 days, and then declined gradually toward normal values over the next 2 weeks. Furthermore, the effect on the different molecular forms depended strongly on the stimulus pattern. Thus, intermittent 100 Hz stimulation (fast pattern) induced essentially the three forms typical of the normal EDL, whereas continuous 10 Hz stimulation induced the six forms characteristic of normal soleus muscles but with some differences in their relative proportions. In the EDL, 2 days of continuous 10 Hz stimulation (the only duration and pattern examined) failed to induce a similar increase in AChE activity.