SYNTHESIS AND RELEASE OF AN ACETYLCHOLINE-LIKE COMPOUND BY HUMAN MYOBLASTS AND MYOTUBES

1. Exogenously applied acetylcholine (ACh) is a modulator of human myo blast fusion. Using a chemiluminescent method, we examined whether an endogenous ACh-like compound (ACh-lc) was present in, and released by, pure human myogenic cells. 2. Single, freshly isolated satellite cell s and proliferating myoblasts contained 15 and 0.5 fmol ACh-lc, respec tively. Cultured myotubes contained ACh-lc as well. Also, ACh-like imm unoreactivity was detected in all myogenic cells. 3. Part of the ACh-l c was synthesized by choline acetyltransferase (ChAT), as indicated by the reduction of ACh-lc content when bromoACh was present in the cult ure medium, and by direct measurements of ChAT activity. Also, ChAT-li ke immunoreactivity mas observed in all myogenic cells. 4. Myoblasts a nd myotubes released ACh-lc spontaneously by a partially Ca2+-dependen t mechanism. 5. The application by microperfusion of medium conditione d beforehand by myoblasts (thus presumably containing ACh-lc) onto a v oltage-clamped myotube induced inward currents resembling ACh-induced currents in their kinetics, reversal potential, and sensitivity to nic otinic antagonists. 6. In vitro, the spontaneously released ACh-lc pro moted myoblast fusion but only in the presence of an anticholinesteras e. 7. Our observations indicate that human myogenic cells synthesize a nd release an ACh-lc and thereby promote the fusion process that occur s in muscle during growth or regeneration.