Ionotropic receptor with a probable role in the modulation of auditory stimuli. Agonist binding induces a conformation change that leads to the opening of an ion-conducting channel across the plasma membrane (PubMed:11752216, PubMed:25282151). The channel is permeable to a range of divalent cations including calcium, the influx of which may activate a potassium current which hyperpolarizes the cell membrane (PubMed:11752216, PubMed:25282151). In the ear, this may lead to a reduction in basilar membrane motion, altering the activity of auditory nerve fibers and reducing the range of dynamic hearing. This may protect against acoustic trauma. May also regulate keratinocyte adhesion (PubMed:11021840). Can form homo- or heterooligomeric channels in conjunction with CHRNA10 (PubMed:11752216). The native outer hair cell receptor may be composed of CHRNA9-CHRNA10 heterooligomers. Interacts with the alpha-conotoxon RgIA (PubMed:22774872). Expressed in cochlea, keratinocytes, pituitary gland, B-cells and T-cells. N-glycosylated. The heterooligomeric receptor composed of CHRNA9 and CHRNA10 has an atypical pharmacological profile, binding several non-nicotinic ligands including strychnine (a glycine receptor antagonist) and atropine (a muscarinic acetylcholine receptor antagonist). Belongs to the ligand-gated ion channel (TC 1.A.9) family. Acetylcholine receptor (TC 1.A.9.1) subfamily. Alpha-9/CHRNA9 sub-subfamily.