title: Allosteric modulation of [3H]dizocilpine binding to N-methyl-D-aspartate receptor by an endogenous Na+, K+-ATPase inhibitor: dependence on receptor activation.
abstract: An endogenous Na(+), K(+)-ATPase inhibitor, termed endobain E, has been isolated from rat brain and proved to decrease [3H]dizocilpine binding to cerebral cortex N-methyl-D-aspartate (NMDA) receptor, an effect independent of sodium pump activity. The purpose of this study was to disclose the mechanism of [3H]dizocilpine binding reduction by endobain E by performing saturation, kinetic and competitive assays. In saturation binding assays, endobain E increased K(d) without modifying B(max) value. To determine whether competitive or allosteric interaction was involved, kinetics of [3H]dizocilpine binding to cerebral cortex membranes was studied. Endobain E increased [3H]dizocilpine dissociation rate constant and induced an initial fast phase, without modifying association rate constant, indicating an allosteric interaction. In competitive [3H]dizocilpine binding assays, no additive effect was observed with endobain E plus competitive antagonists for glutamate or glycine sites (2-amino-5-phosphonopentanoic acid (AP-5) and 7-chlorokynurenic acid, respectively), indicating that coagonist site blockade interferes with endobain E effect. However, the higher glutamate and glycine concentration, the greater its effect. Endobain E binding reduction was partially additive with that induced by ketamine or Mg(2+) (receptor-associated channel blockers). Results suggest that the greater the channel activation by glutamate and glycine, the greater endobain E allosteric effect. Furthermore, as ketamine and Mg(2+) interfere with endobain E effect, this factor most likely binds to the inner surface of the NMDA associated channel.
authors.affiliation: Instituto de Biología Celular y Neurociencias "Prof. E. De Robertis", Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Analía
authors.initials: A
authors.lastname: Reinés
authors.forename: Clara
authors.initials: C
authors.lastname: Peña
authors.forename: Georgina
authors.initials: G
authors.lastname: Rodríguez de Lores Arnaiz
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects; D002614:Chelating Agents / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D018698:Glutamic Acid / Q000493:pharmacokinetics; D005998:Glycine / Q000493:pharmacokinetics; D007649:Ketamine / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D010042:Ouabain / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism*; D012044:Regression Analysis; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013997:Time Factors; D014316:Tritium / Q000493:pharmacokinetics
chemical_list: D002614:Chelating Agents; D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; C119205:endobain E; D014316:Tritium; D018698:Glutamic Acid; D004533:Egtazic Acid; D010042:Ouabain; D007649:Ketamine; D016291:Dizocilpine Maleate; D004492:Edetic Acid; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D005998:Glycine