Effect of mechanical load on acetylcholinesterase mRNA levels in the slow soleus muscle of the rat

The influence of mechanical load on the levels of acetylcholinesterase (ACh E) mRNA was studied in order to examine to which extent different loading c onditions may be responsible for differences in AChE regulation between the soleus, which is an antigravity muscle, and the fast EDL muscle. Forty-eig ht female rats were randomly assigned to three groups: a group with hindlim b suspension producing soleus muscle unloading, a group with ablation of sy nergistic gastrocnemius muscle causing overload of the soleus muscle, and t he control group. The soleus muscles were isolated after 8 days of treatmen t. AChE mRNA levels were analyzed by Northern blots and evaluated densitome trically. The values were normalized with beta-actin mRNA level, and then a value of 100% was assigned to the mRNA level in the control EDL muscle. Mu scle unloading did not produce a significant increase of the AChE transcrip t levels, but the levels were rather variable. However, a statistically sig nificant increase of AChE mRNA levels was observed in overloaded soleus mus cles. These results corroborate the hypothesis that the slow and fast patte rns of activity appear more important then muscle loading for the differenc es in regulation of AChE mRNA levels in fast and slow muscles.