title: Modulation of the Ca(2+) permeability of human endplate acetylcholine receptor-channel.
abstract: In slow-channel congenital myasthenic syndrome, point mutations of the endplate acetylcholine receptor (AChR) prolong channel openings, leading to excessive Ca(2+) entry with ensuing endplate degeneration and myasthenic symptoms. The Ca(2+) permeability of the human endplate AChR-channel is quite high, and is further increased by two slow-channel mutations in its ɛ subunit, worsening the pathological cascade. To gain further support to the hypothesis that the ɛ subunit plays a crucial role in controlling Ca(2+) permeability of endplate AChR-channel, in this work we measured the fractional Ca(2+) current (P(f), i.e., the percentage of the total current carried by Ca(2+) ions) of a panel of AChR carrying slow-channel mutations in the α, β and ɛ subunits detected in patients (α(N217K), α(S226Y), α(C418W), β(V266A), β(V266M), ɛ(I257F), ɛ(V265A) and ɛ(L269F)). We confirm that only mutations in the ɛ subunit altered Ca(2+) permeability of AChR-channels, with ɛ(L269F) increasing P(f) (10% vs. 7% of wild type AChR) and ɛ(I257F) decreasing it (to 4.6%). We also found that, for ɛ(L269F)-AChR, the Ca(2+) permeability and ACh-induced cell death can be normalized by clinically relevant concentrations of salbutamol or verapamil, providing the first evidence that the Ca(2+) permeability of AChR-channels can be modulated and this treatment may provide protection against excitotoxic insults.
authors.affiliation: Dipartimento di Fisiologia e Farmacologia, Sapienza Università di Roma, P.le A. Moro 5, I-00185 Roma, Italy.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Piccari
authors.forename: Cristina
authors.initials: C
authors.lastname: Deflorio
authors.forename: Rachele
authors.initials: R
authors.lastname: Bigi
authors.forename: Francesca
authors.initials: F
authors.lastname: Grassi
authors.forename: Sergio
authors.initials: S
authors.lastname: Fucile
mesh_terms: D000420:Albuterol / Q000494:pharmacology; D019943:Amino Acid Substitution; D000818:Animals; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D009045:Motor Endplate / Q000502:physiology*; D009154:Mutation; D020294:Myasthenic Syndromes, Congenital / Q000378:metabolism / Q000473:pathology; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011950:Receptors, Cholinergic / Q000235:genetics / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D021122:Protein Subunits; D011950:Receptors, Cholinergic; D014700:Verapamil; D000420:Albuterol; D002118:Calcium