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; homomeric complex is functional but exhibits low conductance with modified voltage dependence, and decreased agonist and antagonist affinity. Interacts with RIC3 (By similarity). Brain, spinal cord, and heart. The HA-stretch region of HTR3A seems to be responsible for the low conductance of HTR3A homomers compared to that of HTR3A/HTR3B heteromers. Belongs to the ligand-gated ion channel (TC 1.A.9) family. 5-hydroxytryptamine receptor (TC 1.A.9.2) subfamily. HTR3A sub-subfamily.