K. Zajc Kreft, S. Kreft, and Z. Grubiè Institute of Pathophysiology, Medical Faculty, Ljubljana, Slovenia

Acetylcholinesterase (AChE) mRNA in fast rat skeletal muscle is downregulated by both, electromechanical activity and denervation. One candidate mechanism that could explain decreased level of AChE mRNA in the denervated muscle is increased rate of its degradation. In order to test this possibility, total deproteinated RNA was isolated from rat m. SM and exposed to subcellular muscular fractions prepared from contralateral m.SM. After selected time intervals, we determined remaining AChE mRNA by nonradioactive Northern blot analysis. AChE mRNA remained at the same level during first 5 hours after denervation and abruptly fell after subsequent 13h. Further decrease in the transcript level proceeded at much slower rate. Longer transcript (3.5 kb) was more affected than the shorter (2.3 kb) one. The level of a-actin mRNA was also decreased in the denervated muscle, and the rate of its disappearance was similar to that of AChE mRNA, suggesting that AChE mRNA is not specifically affected under such conditions. Degradation of AChE mRNA was observed in all subcellular fractions studied. Postmitochondrial and postpolysomal fractions exibited higher rate than polysomal fraction. We find experimental approach demonstrated here suitable for studies of degradation capacities of the specific mRNAs in the adult skeletal muscles. Our preliminary results suggest, that fall of AChE mRNA after denervation at least partly results from increased degradation of transcripts under such conditions..