ACETYLCHOLINESTERASE ADAPTATION TO VOLUNTARY WHEEL RUNNING IS PROPORTIONAL TO THE VOLUME OF ACTIVITY IN FAST, BUT NOT SLOW, RAT HINDLIMB MUSCLES

Chronic enhancement of neuromuscular activity by forced exercise train ing programmes results in selective adaptation of the G(4) acetylcholi nesterase (AChE) molecular form in hindlimb fast muscles of the rat, w ith only minor and non-selective AChE changes in the soleus. In order to shed further light on the physiological significance of this G(4) a daptation to training, we turned to a voluntary exercise model. The im pact of 5 days and 4 weeks of voluntary wheel cage running on AChE mol ecular forms was examined in four hindlimb fast muscles and the slow-t witch soleus from two rat strains. Inbred Fisher and Sprague-Dawley ra ts, placed in live-in wheel cages, exercised spontaneously for distanc es which progressively increased up to an average of similar to 3 and 18 km/day, respectively, by the end of week 4. Fast muscles responded to this voluntary activity by massive G(4) increases (up to 420%) with almost no changes in A(12), so that by week 4 the tetramer became the main AChE component of these muscles. The additional G(4) was compose d primarily of amphiphilic molecules, suggesting a membrane-bound stat e. The G(4) content of fast muscles was highly correlated with the dis tance covered by the rats during the 5 days before they were killed (r = 0.850-0.879, P < 0.001 in three muscles). The soleus muscle, in tur n, responded to wheel cage activity by a marked selective reduction of its asymmetric forms-up to 45% for A(12). This A(12) decline, already maximal by day 5 of wheel cage running, showed no relationship with t he distance covered. The present results constitute strong new evidenc e suggesting that the role of AChE in neuromuscular transmission is no t limited solely to the rapid inactivation of just-released acetylchol ine.