Spontaneous opening of the acetylcholine receptor channel in developing muscle cells from normal and dystrophic mice

Abstract

Single-channel activity was recorded from cell-attached patches on skeletal muscle cells isolated from wild-type mice and from mice carrying the dy or mdx mutations. Spontaneous openings of the nicotinic acetylcholine receptor channel (nAChR) were detected in virtually all recordings from either dy/dy or dy/+ myotubes, but only infrequently from wild-type or mdx myotubes. Spontaneous openings were also present in most recordings from undifferentiated myoblasts from all of the mouse strains studied. The biophysical properties of the spontaneous activity were similar to those of the embryonic form of the nAChR in the presence of acetylcholine (ACh). Examination of the single-channel currents evoked by low concentrations of ACh showed a reduced sensitivity to the agonist in the dystrophic dy and mdx myotubes, but not in wild-type myotubes. The results suggest that alterations in nAChR function are associated with the pathogenesis of muscular dystrophy in the dy mouse.

Autocrine activation of nicotinic acetylcholine receptors contributes to Ca2+ spikes in mouse myotubes during myogenesis

“…4). In accordance with previous reports (Jackson, 1984, 1986; Franco‐Obregón & Lansman, 1995), the biophysical and pharmacological properties of such openings partially resembled those of the embryonic muscle nAChR channels recorded in the presence of ACh in the pipette. Indeed, the single channel openings were characterized by a conductance of 27.79 ± 2.62 pS, and the open‐time histograms were best fitted with two exponentials: brief and long time constants were of 0.21 ± 0.02 ms (72.2% of all the events) and 1.78 ± 0.24 ms, respectively ( n = 8; data not shown).…”

“…As, in myotubes, the embryonic nAChR are evenly distributed on the membrane, it has been proposed that such a diffuse expression of the receptors might make the muscle cells particularly receptive to innervation and improve the likelihood of synaptic formation (Nakajima et al 1987; Brehm & Henderson, 1988; see also Lin et al 2001; Yang et al 2001; Misgeld et al 2002). Furthermore, it has been demonstrated that openings of the embryonic nAChR channels occur as spontaneous events in myotubes (Jackson, 1984, 1986; Franco‐Obregón & Lansman, 1995). Therefore, after cell fusion, the nAChRs could be important not only for their localization at the cell membrane level but also for their own activity.…”

Combination of agrin and laminin increase acetylcholine receptor clustering and enhance functional neuromuscular junction formation In vitro

“…However, this measure of innervation was confounded by the presence of minimal levels of acetylcholine mediated spontaneous contractions in uninnervated myotube cultures. Spontaneous myotube contractions are due to a combination of autocrine activation of AChR and spontaneous opening of AChR associated ion channels (Land et al, ; Sherman et al, ; Franco‐Obregon and Lansman, ; Sciancalepore et al, ). Myotubes alone can synthesize an acetylcholine like compound that acts in an autocrine fashion to promote spontaneous myotube contraction (Hamann et al, ; Bandi et al, ).…”

Enhanced homosynaptic LTD in cerebellar Purkinje cells of the dystrophic MDX mouse

“…It has long been known that the absence of dystrophin can cause a pathological functioning of membrane ion channels. 21 Haws and Lansman 22 reported that mdx granular cells contained a Ca 2þ permeable channel that was open at rest. This finding was supported by work from Steinhardt's group, 23 who used Ca 2þ -sensitive dyes to demonstrate that resting Ca 2þ was elevated in cultured mdx granular cells.…”