Editing Acetylcholine receptor (section)

===nAChR===
{{Main|Nicotinic acetylcholine receptor}}
The nAChRs are [[ligand-gated ion channel]]s, and, like other members of the "[[cys-loop]]" ligand-gated ion channel superfamily, are composed of five [[protein subunit]]s symmetrically arranged like staves around a barrel. The subunit composition is highly variable across different tissues. Each subunit contains four regions which span the membrane and consist of approximately 20 amino acids.  Region II which sits closest to the pore lumen, forms the pore lining.{{cn|date=April 2025}}

Binding of acetylcholine to the N termini of each of the two alpha subunits results in the 15° rotation of all M2 helices.<ref name="pmid15165732">{{cite journal | author = Doyle DA | title = Structural changes during ion channel gating | journal = Trends Neurosci. | volume = 27 | issue = 6 | pages = 298–302 | year = 2004 | pmid = 15165732 | doi = 10.1016/j.tins.2004.04.004 | s2cid = 36451231 }}</ref> The cytoplasm side of the nAChR receptor has rings of high negative charge that determine the specific cation specificity of the receptor and remove the hydration shell often formed by ions in aqueous solution. In the intermediate region of the receptor, within the pore lumen, [[valine]] and [[leucine]] residues (Val 255 and Leu 251) define a hydrophobic region through which the dehydrated ion must pass.<ref name="pmid12827192">{{cite journal |vauthors=Miyazawa A, Fujiyoshi Y, Unwin N | title = Structure and gating mechanism of the acetylcholine receptor pore | journal = Nature | volume = 423 | issue = 6943 | pages = 949–55 | year = 2003 | pmid = 12827192 | doi = 10.1038/nature01748 | bibcode = 2003Natur.423..949M | s2cid = 205209809 }}</ref>

The nAChR is found at the [[Postsynaptic density|edges of junctional folds]] at the [[neuromuscular junction]] on the postsynaptic side; it is activated by [[acetylcholine]] release across the synapse. The diffusion of Na<sup>+</sup> and K<sup>+</sup> across the receptor causes depolarization, the end-plate potential, that opens [[voltage-gated sodium channel]]s, which allows for firing of the [[action potential]] and potentially muscular contraction.{{cn|date=April 2025}}