5-hydroxytryptamine receptor 3B (5-HT3B)

The **5-hydroxytryptamine receptor 3B (5‑HT₃B)** is a protein that forms part of the type 3 serotonin receptor complex. Unlike most serotonin receptors—which are G protein-coupled—the type 3 family are ligand-gated ion channels belonging to the Cys-loop superfamily. The functional native human receptor is a pentameric assembly usually composed of both A and B subunits; homomeric A assemblies can form functional channels alone, but inclusion of B alters key properties such as single-channel conductance and calcium permeability. The presence or absence of the B subunit modulates physiological responses including rapid excitatory neurotransmission in both central and peripheral nervous systems. The gene encoding this subunit (**HTR3B**) is expressed broadly across tissues including brain regions involved in emesis control, mood regulation, pain perception, gastrointestinal function, kidney, liver—and shows isoform-specific expression patterns. Clinically important drugs such as ondansetron exert their antiemetic effect by antagonizing these receptors; genetic variation within HTR3B may influence individual drug response or disease risk profiles. Overall, while not directly forming a therapeutic target on its own—since it does not form functional homomeric channels—the **5‑HT₃B subunit is essential for defining pharmacological properties when co-expressed with A**, making it highly relevant for understanding serotonergic signaling modulation by drugs.

Other names

HTR3BSerotonin receptor 3B subunit5-HT3 receptor subunit B

Drugs targeting this molecule typically act as **antagonists**, blocking serotonin binding to the receptor complex and thereby inhibiting the associated cation influx that leads to neuronal excitation. This mechanism is central to their antiemetic effects.