The 5-HT3 Receptor
5-Hydroxytryptamine (5-HT), also known as serotonin, was initially identified as a potent vasoconstrictor present in blood serum (Rapport et al. 1947). It is now clear 5-HT has a multitude of functions including activation or inhibition of muscle, exocrine and endocrine glands, central and peripheral neurons, and cells of the hematopoietic and immune systems. 5-HT receptors were initially subdivided into D and M subtypes, based on their sensitivity to dibenyline or morphine (Gaddum and Picarelli 1957). Currently, 5-HT receptors are divided into seven major families (5-HT1-7) based on transduction and structural characteristics. All are G-protein-coupled receptors, except for the 5-HT3 receptor which is a ligand-gated ion channel (LGIC), and indeed, it is this receptor which is the original M receptor.
The 5-HT3receptor is a cation-selective member of the Cys-loop family of LGIC. The receptors are...