title: 2', 3'-O-(2,4,6,trinitrophenyl)-ATP and A-317491 are competitive antagonists at a slowly desensitizing chimeric human P2X3 receptor.
abstract: (1) Rapid desensitization of ligand-gated ion channel receptors can alter the apparent activity of receptor modulators, as well as make detection of fast-channel activation difficult. Investigation of the antagonist pharmacology of ATP-sensitive homomeric P2X3 receptors is limited by agonist-evoked fast-desensitization kinetics. (2) In the present studies, chimeric receptors were created using the coding sequence for the N-terminus and the first transmembrane domain of either the nondesensitizing human P2X2a or fast-desensitizing P2X3 receptor joined to the sequence encoding the extracellular loop, second transmembrane domain, and C-terminus of the other receptor (designated P2X2-3 and P2X3-2, respectively). These clones were stably transfected into 1321N1 astrocytoma cells for biophysical and pharmacological experiments using both electrophysiological and calcium-imaging methods. (3) Chimeric P2X2-3 and P2X3-2 receptors were inwardly rectifying and agonist responses showed desensitization properties similar to the wild-type human P2X2a and P2X3 receptors, respectively. (4) The P2X2-3 chimera displayed an agonist pharmacological profile similar to the P2X3 wild-type receptor being activated by low concentrations of both ATP and alpha,beta-meATP. In contrast, the P2X3-2 chimera had markedly reduced sensitivity to both agonists. (5) The P2X3 receptor antagonists TNP-ATP and A-317491 were shown to be potent, competitive antagonists of the P2X2-3 chimera (Ki=2.2 and 52.1 nm, respectively), supporting the hypothesis that rapid receptor desensitization can mask the competitive antagonism of wild-type homomeric P2X3 receptors.
authors.affiliation: Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, USA.
authors.forename: Torben R
authors.initials: TR
authors.lastname: Neelands
authors.forename: Edward C
authors.initials: EC
authors.lastname: Burgard
authors.forename: Marie E
authors.initials: ME
authors.lastname: Uchic
authors.forename: Heath A
authors.initials: HA
authors.lastname: McDonald
authors.forename: Wende
authors.initials: W
authors.lastname: Niforatos
authors.forename: Connie R
authors.initials: CR
authors.lastname: Faltynek
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Lynch
authors.forename: Michael F
authors.initials: MF
authors.lastname: Jarvis
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006801:Humans; D010636:Phenols / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011083:Polycyclic Compounds / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058477:Receptors, Purinergic P2X3
chemical_list: C470346:A-317491; C546407:P2RX3 protein, human; D010636:Phenols; D011083:Polycyclic Compounds; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058477:Receptors, Purinergic P2X3; C045674:2',3'-O-(2,4,6-trinitro-cyclohexadienylidine)adenosine 5'-triphosphate; D000255:Adenosine Triphosphate