Fig. 1.

Structural organization nicotinic acetylcholine receptors. (A) nAChRs are pentameric ligand-gated cationic channels. nAChR agonists, such as acetylcholine and nicotine, stabilize the receptor in the active confirmation associated with an open transmembrane pore permeable to calcium sodium (Na⁺), potassium (K⁺), and (Ca²⁺) ions. Prolonged stimulation of the receptor by agonists, such as nicotine, can drive the receptor into an inactive “desensitized” state. (B) Major stoichiometries of homopentameric or heteropentameric nAChRs expressed in the mammalian brain. The open white circles indicate that one of the adjacent subunits contained within the adjacent box are often incorporated into that nAChR subtype.