The ion channel of the nicotinic acetylcholine receptor is formed by the homologous helices M II of the receptor subunits

AbstractA binding site for the channel-blocking noncompetitive antagonist [3H]triphenylmethylphosphonium ([3H]TPMP+) was localized in the α-, β- and δ-chains of the nicotinic acetylcholine receptor (AChR) from Torpedo marmorata electric tissue. The photolabel was found in homologous positions of the highly conserved sequence helix II, α 248, β 254, and δ 262. The site of the photoreaction appears to not be affected by the functional state of the receptor. [3H]TPMP+ was found in position δ 262 independent of whether photolabeling was performed with the receptor in its resting, desensitized or antagonist state. A model of the AChR ion channel is proposed, according to which the channel is formed by the five helices II contributed by the five receptor subunits