MECHANICAL STIMULATION INCREASES EXPRESSION OF ACETYLCHOLINESTERASE IN CULTURED MYOTUBES

We tested the hypothesis that acetylcholinesterase (AChE) expression i n skeletal muscle cells is increased by passive mechanical stimulation . To this end, primary cultures of myotubes were subjected to repeated cycles of stretch-relaxation for 5 min, 30 min, 3 h, and 24 h, using the Flexercell FX-2000 strain unit. Although mechanical stimulation di d not affect AChE expression at early time points, it led to a signifi cant increase (42%; P < 0.05) in total AChE activity at 24 h. This inc rease reflected a general elevation in the activity of all AChE molecu lar forms as opposed to a preferential increase in a specific form. Te trodotoxin (TTX) treatment did not prevent the increase in AChE: expre ssion, whereas nifedipine partially blocked it. These changes in enzym e expression were accompanied by increases in the levels of AChE mRNA, suggesting the involvement of pretranslational regulatory mechanisms. Together, these results illustrate that, in addition to neural activa tion and trophic factors, passive mechanical forces modulate expressio n of AChE in skeletal muscle cells. Because TTX did not prevent the in crease in AChE expression, it appears that the effects of mechanical s timulation are independent of electrical activity, which further indic ates the use of an alternate signaling pathway.