5-HT 3 Rs are members of the Cys-loop family of ligand-gated ion channels which also includes nACh, GABA A , and glycine receptors. 4 These transmembrane proteins enable rapid synaptic transmission in the central and peripheral nervous system and are composed of five pseudosymmetrically arranged subunits surrounding a central ion-conducting pore. The neurotransmitter binding sites are located in the extracellular N-terminal domains at the interface of two adjacent ...