Fig. 1.

Basic structure of neuronal nAChRs. (A) A nAChR is composed of five subunits. Each subunit contains four transmembrane domains (M1–M4). An amine functional group is located at the end of the M1 transmembrane domain, whereas a carboxyl group is located at the end of the M4 transmembrane domain (insert). When an agonist (e.g., acetylcholine, nicotine) binds an orthosteric site, extracellular sodium and calcium enter the cell. (B) Diagram of the pentameric structure of neuronal nAChRs, which can be heteromeric (e.g., α4β2, α4α5β2) or homomeric (e.g., α7) in composition.