This is one of the several different receptors for 5-hydroxytryptamine (serotonin), a biogenic hormone that functions as a neurotransmitter, a hormone, and a mitogen. This receptor is a ligand-gated ion channel, which when activated causes fast, depolarizing responses in neurons. It is a cation-specific, but otherwise relatively nonselective, ion channel. Forms pentahomomeric complex as well as pentaheteromeric complex with HTR3B or HTR3C or HTR3D or HTR3E; homomeric complex is functional but exhibits low conductance with modified voltage dependence, and decreased agonist and antagonist affinity. Interacts with RIC3 (By similarity). Expressed in cortex, intestine and liver. Not expressed in muscle or spleen. Belongs to the ligand-gated ion channel (TC 1.A.9) family. 5-hydroxytryptamine receptor (TC 1.A.9.2) subfamily. HTR3A sub-subfamily.