Synthesis and release of an acetylcholine‐like compound by human myoblasts and myotubes.

Abstract

1. Exogenously applied acetylcholine (ACh) is a modulator of human myoblast 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 cells and proliferating myoblasts contained 15 and 0.5 fmol ACh‐lc, respectively. Cultured myotubes contained ACh‐lc as well. Also, ACh‐like immunoreactivity was detected in all myogenic cells. 3. Part of the ACh‐lc was synthesized by choline acetyltransferase (ChAT), as indicated by the reduction of ACh‐lc content when bromoACh was present in the culture medium, and by direct measurements of ChAT activity. Also, ChAT‐like immunoreactivity was observed in all myogenic cells. 4. Myoblasts and myotubes released ACh‐lc spontaneously by a partially Ca(2+)‐dependent mechanism. 5. The application by microperfusion of medium conditioned beforehand by myoblasts (thus presumably containing ACh‐lc) onto a voltage‐clamped myotube induced inward currents resembling ACh‐induced currents in their kinetics, reversal potential, and sensitivity to nicotinic antagonists. 6. In vitro, the spontaneously released ACh‐lc promoted myoblast fusion but only in the presence of an anticholinesterase. 7. Our observations indicate that human myogenic cells synthesize and release an ACh‐lc and thereby promote the fusion process that occurs in muscle during growth or regeneration.

T-type α1H Ca 2+ channels are involved in Ca 2+ signaling during terminal differentiation (fusion) of human myoblasts

“…However, an up-regulation of T-channel expression immediately after fusion cannot be excluded. Another explanation for the low percentage of fusion-competent myoblasts with high [Ca 2ϩ ] i is that myoblasts normally stimulate one another by autocrine mechanisms (31) and that this is less likely to occur in low density cultures. Finally, as we shall discuss below, it is also possible that the [Ca 2ϩ ] i oscillates in fusioncompetent myoblasts so that, at a given time, only a fraction of the cells can be detected with a high [Ca 2ϩ ] i .…”

“…A Ca 2ϩ -ATPase muscle-specific isoform is expressed at myotube formation in mouse C2 myoblasts (32). Another possible way of reducing Ca 2ϩ entry would be the activation of Ca Interestingly, an effect of the window T-current could be mediated by an acetylcholine-like compound that human myoblasts synthesize and release in a Ca 2ϩ dependent way (31). As acetylcholine has been shown to accelerate fusion (16), Ca 2ϩ entering through the window of the ␣1H T-channel of fusioncompetent myoblasts could trigger release of this compound and thereby favor differentiation of neighboring cells, or contribute to further increase [Ca 2ϩ ] i through muscle nicotinic acetylcholine receptors, which are permeable to Ca 2ϩ (33).…”

Immunohistochemical evidence suggests intrinsic regulatory activity of human eccrine sweat glands

“…Our results indicate that acetylcholine could be synthesised in myoepithelial cells. This is not entirely surprising because ChAT has been found in nonneuronal human tissues, namely ejaculated spermatozoa (Ibanez et al 1991), myoblasts and myotubes (Hamann et al 1995) and the chorion (Oda et al 1996). Myoepithelial cells subserve the rapid excretion of sweat on stimulation and\or ' provide mechanical support for the secretory coil wall against the increase in luminal hydrostatic pressure ' (Sato et al 1989), and the ChAT activity therein could contribute to regulation of contractile activity.…”

Basic and Clinical Aspects of Non-neuronal Acetylcholine: Overview of Non-neuronal Cholinergic Systems and Their Biological Significance

“…Later, Hamann et al (76) found that proliferating myoblasts contained a small amount of ACh-like compound and that this compound was synthesized by BrACh-sensitive ChAT in all myogenic cells. The ACh-like compound was spontaneously released from both myoblasts and myotubes in a partially Ca 2+ -dependent manner.…”