title: N-methyl-D-aspartate/glycine and quisqualate/kainate receptors expressed in Xenopus oocytes: antagonist pharmacology.
abstract: Quantitative pharmacological studies were done to determine the properties of excitatory amino acid receptors expressed in Xenopus oocytes injected with rat brain mRNA. Smooth currents with properties indicative of N-methyl-D-aspartate (NMDA) and quisqualate/kainate receptors were observed in mRNA-injected oocytes. Schild analysis of currents evoked by NMDA indicated that the EAA receptor antagonist D-2-amino-5-phosphonovalerate (D-APV) exerted a competitive block of the oocyte NMDA receptor, because the Schild regression was linear with a slope not significantly different from unity (1.03 +/- 0.025) up to 100 microM D-APV. The pA2 estimated for D-APV antagonism of NMDA currents (5.87 +/- 0.043) was nearly identical to that for D-APV as an L-aspartate antagonist (pA2 = 5.86 +/- 0.073, slope = 0.97 +/- 0.036), suggesting that these two agonists are selective for NMDA receptors in oocytes up to concentrations well above 1 mM. 6-Nitro-7-cyano-quinoxaline-2,3-dione (CNQX) reduced the maximum NMDA response significantly (70% reduction by 15 microM CNQX) but had no effect on the NMDA EC50. CNQX exerted a mixed competitive-noncompetitive block of the glycine site on NMDA receptors; 15 microM CNQX increased the glycine EC50 by 5-fold and reduced the maximum glycine response by 35%. In addition, CNQX exerted a potent and competitive antagonism of currents evoked by kainate. The Schild regression was linear up to 30 microM CNQX with a slope of 1.02 +/- 0.014 and a pA2 of 6.53 +/- 0.029. The block of kainate or NMDA currents by 2 microM CNQX was not voltage dependent. D-APV exerted a weak antagonism of kainate-evoked currents, with a pA2 of 3.39 +/- 0.044, but the slope of the Schild regression was slightly less than 1 (0.90 +/- 0.03). These data demonstrate a clear pharmacological distinction between receptors that mediate the kainate- and NMDA-induced currents and quantify the potency of CNQX and D-APV acting at NMDA/glycine and quisqualate/kainate receptors. The implications of these data for the identification of EAA receptors in oocytes and the classification of neuronal EAA receptors are discussed.
authors.affiliation: Department of Pharmacology, University of North Carolina, Chapel Hill 27599.
authors.forename: T A
authors.initials: TA
authors.lastname: Verdoorn
authors.forename: N W
authors.initials: NW
authors.lastname: Kleckner
authors.forename: R
authors.initials: R
authors.lastname: Dingledine
mesh_terms: D015763:2-Amino-5-phosphonovalerate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors; D007608:Kainic Acid / Q000037:antagonists & inhibitors; D016202:N-Methylaspartate; D009865:Oocytes / Q000187:drug effects; D011810:Quinoxalines / Q000494:pharmacology; D018091:Receptors, AMPA; D018009:Receptors, Glycine; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000032:analysis / Q000187:drug effects*; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D015763:2-Amino-5-phosphonovalerate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D001224:Aspartic Acid; D007608:Kainic Acid; D016202:N-Methylaspartate; D011810:Quinoxalines; D018091:Receptors, AMPA; D018009:Receptors, Glycine; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D014633:Valine