Serotonin receptor subtype 3A (5-HT3A)

The **serotonin receptor subtype 3A (5-HT3A)** is a ligand-gated ion channel that forms the central functional unit of the 5-HT3 receptor, the only serotonin receptor subtype in humans that is not G protein-coupled but rather a member of the Cys-loop superfamily of ion channels[1][2][4][6]. The receptor is encoded by the **HTR3A gene** and forms homopentameric channels capable of mediating fast excitatory neurotransmission upon activation by serotonin. 5-HT3A is widely expressed in both the central and peripheral nervous systems, including on sensory neurons involved in pain signaling and in the enteric nervous system. It is a major target for antiemetic drugs used in chemotherapy-induced nausea and vomiting, as well as for agents addressing irritable bowel syndrome[1][3][5][8]. Functional and structural studies have shown 5-HT3A forms homopentamers, or can combine with other subunits (such as 5-HT3B) to form heteropentamers, altering channel properties[1][6][8]. 5-HT3A-mediated channels enable rapid cation (Na⁺, K⁺, Ca²⁺) influx, directly depolarizing neurons. Because of its role in nausea, emesis, pain, and gastrointestinal physiology, it is an important therapeutic target. Genetic variants can affect drug responses, and inhibitors (setrons) are key in cancer supportive care but may pose specific safety risks (notably cardiac)[1][4][8].

Other names

5-HT3A receptor5-hydroxytryptamine receptor 3AHTR3A5-HT3 (when referring to the dominant homomeric form)

Competitive antagonism (setrons: block 5-HT3A and prevent serotonin-induced cation influx) - Negative allosteric modulation (some ligands)