The<unk>  differs markedly in structure and mechanism from the other<unk>  subtypes, which are all G-protein-coupled. A functional channel may be composed of five identical<unk> -HT3A subunits (homopentameric) or a mixture of<unk> -HT3A and one of the other four<unk> -HT3B,<unk> -HT3C,<unk> -HT3D, or<unk> -HT3E subunits (heteropentameric). It appears that only the<unk> -HT3A subunits form functional homopentameric channels. All other subunit subtypes must heteropentamerize with<unk> -HT3A subunits to form functional channels. Additionally, there has not currently been any pharmacological difference found between the heteromeric<unk> -HT3AC,<unk> -HT3AD,<unk> -HT3AE, and the homomeric<unk> . N-terminal glycosylation of<unk>  subunits is critical for subunit assembly and plasma membrane trafficking. Figure 2. The subunits are assembled as a pentamer (right) and each subunit has four transmembrane domains (left). The subunits surround a central ion channel in a pseudo-symmetric manner (Fig.1). Each subunit comprises an extracellular N-terminal domain which comprises the orthosteric ligand-binding site; a transmembrane domain consisting of four interconnected alpha helices (M1-M4), with the extracellular M2-M3 loop involved in the gating mechanism; a large cytoplasmic domain between M3 and M4 involved in<unk>  trafficking and regulation; and a short extracellular C-terminus (Fig.1). Whereas extracellular domain is the site of action of agonists and competitive antagonists, the transmembrane domain contains the central ion pore,<unk>  gate, and principle selectivity filter that allows ions to cross the cell membrane.
5-HT3 receptor
Muscarinic acetylcholine receptor M4
Baroreceptor
Trace amine-associated receptor
Prolactin-releasing peptide receptor
SK channel
Hydroxycarboxylic acid receptor 2
Norepinephrine transporter