Effect of fibrillation on the secretion of acetylcholinesterase from cultured embryonic rat myotubes.

We have measured acetylcholinesterase (AChE) turnover and secretion in spontaneously fibrillating rat myotubes and in cultures in which fibrillation was blocked with tetrodotoxin. The rate at which AChE appeared in the medium was 4 times greater in fibrillating than in non-fibrillating cultures. In a 2-h interval, 32% of the AChE in fibrillating myotubes and 26% of the AChE in non-fibrillating myotubes turned over. In this interval, secreted AChE accounted for 28% and 16% of the AChE turnover that occurred in fibrillating and non-fibrillating myotubes, respectively.