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. It is a cation-specific, but otherwise relatively nonselective, ion channel. Forms a pentaheteromeric complex with HTR3A. Not functional as a homomeric complex. Presumably retained within the endoplasmic reticulum unless complexed with HTR3A. Expressed in the brain cortex, in the caudate nucleus, the hippocampus, the thalamus and the amygdala. Detected in the kidney and testis as well as in monocytes of the spleen, small and large intestine, uterus, prostate, ovary and placenta. N-glycosylation required for membrane localization. The HA-stretch region of HTR3B seems to confer increased conductance to HTR3A/HTR3B heteromers compared to that of HTR3A homomers. Belongs to the ligand-gated ion channel (TC 1.A.9) family. 5-hydroxytryptamine receptor (TC 1.A.9.2) subfamily. HTR3B sub-subfamily.