P2X receptors in GtoPdb v.2023.1

P2X receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on P2X Receptors [49, 146]) have a trimeric topology [118, 128, 144, 197] with two putative TM domains per P2X subunit, gating primarily Na+, K+ and Ca2+, exceptionally Cl-. The Nomenclature Subcommittee has recommended that for P2X receptors, structural criteria should be the initial basis for nomenclature where possible. X-ray crystallography indicates that functional P2X receptors are trimeric and three agonist molecules are required to bind to a single trimeric assembly in order to activate it [118, 144, 95, 103, 177]. Native receptors may occur as either homotrimers (e.g. P2X1 in smooth muscle) or heterotrimers (e.g. P2X2:P2X3 in the nodose ganglion [280], P2X1:P2X5 in mouse cortical astrocytes [162], and P2X2:P2X5 in mouse dorsal root ganglion, spinal cord and mid pons [53, 234]. P2X2, P2X4 and P2X7 receptor activation can lead to influx of large cationic molecules, such as NMDG+, Yo-Pro, ethidium or propidium iodide [211]. The permeability of the P2X7 receptor is modulated by the amount of cholesterol in the plasma membrane [193]. The hemi-channel pannexin-1 was initially implicated in the action of P2X7 [212], but not P2X2, receptors [41], but this interpretation is probably misleading [215]. Convincing evidence now supports the view that the activated P2X7 receptor is immediately permeable to large cationic molecules, but influx proceeds at a much slower pace than that of the small cations Na+, K+, and Ca2+ [66].