Mechanical stimulation increases expression of acetylcholinesterase in cultured myotubes

We tested the hypothesis that acetylcholinesterase (AChE) expression in 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 did not affect AChE expression at early time points, it led to a significant increase (42%; P < 0.05) in total AChE activity at 24 h. This increase reflected a general elevation in the activity of all AChE molecular forms as opposed to a preferential increase in a specific form. Tetrodotoxin (TTX) treatment did not prevent the increase in AChE expression, whereas nifedipine partially blocked it. These changes in enzyme 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 activation and trophic factors, passive mechanical forces modulate expression of AChE in skeletal muscle cells. Because TTX did not prevent the increase in AChE expression, it appears that the effects of mechanical stimulation are independent of electrical activity, which further indicates the use of an alternate signaling pathway.