title: D-aspartate and NMDA, but not L-aspartate, block AMPA receptors in rat hippocampal neurons.
abstract: 1 The amino acid, D-aspartate, exists in the mammalian brain and is an agonist at the N-methyl-D-aspartate (NMDA) subtype of ionotropic glutamate receptors. Here, for the first time, we studied the actions of D-aspartate on alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate receptors (AMPARs) in acutely isolated rat hippocampal neurons. 2 In the presence of the NMDA receptor channel blocker, MK801, D-aspartate inhibited kainate-induced AMPAR current in hippocampal neurons. The inhibitory action of D-aspartate on kainate-induced AMPAR current was concentration-dependent and was voltage-independent in the tested voltage range (-80 to +60 mV). 3 The estimated EC50 of the L-glutamate-induced AMPAR current was increased in the presence of D-aspartate, while the estimated maximum L-glutamate-induced AMPAR current was not changed. D-aspartate concentration-dependently shifted the dose-response curve of kainate to the right. Schild plot analysis indicated that D-aspartate acts competitively to block AMPARs. The K(b) for D-aspartate was estimated to be 0.93 mM. 4 D-aspartate also blocked L-glutamate-induced current in Xenopus laevis oocytes that expressed recombinant homomeric AMPARs. 5 NMDA possessed similar inhibitory action on AMPARs. However, L-aspartate had little inhibitory action on AMPARs. 6 D-Aspartate, but not L-aspartate, was found to reduce the amplitude of miniature excitatory postsynaptic current in cultured hippocampal neurons. 7 Our data are consistent with a model in which D-aspartate directly competes with kainate and L-glutamate in binding to the agonist binding site of AMPARs. The prevalence of D-aspartate in the brain suggests a possible role of D-aspartate in modulating AMPAR-mediated fast excitatory synaptic transmission.
authors.affiliation: Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada N6A 5C1.
authors.forename: Xiang-Qun
authors.initials: XQ
authors.lastname: Gong
authors.forename: Anne
authors.initials: A
authors.lastname: Frandsen
authors.forename: Wei-Yang
authors.initials: WY
authors.lastname: Lu
authors.forename: Yudi
authors.initials: Y
authors.lastname: Wan
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Zabek
authors.forename: Darryl S
authors.initials: DS
authors.lastname: Pickering
authors.forename: Donglin
authors.initials: D
authors.lastname: Bai
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D026603:D-Aspartic Acid / Q000737:chemistry / Q000494:pharmacology*; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D007608:Kainic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008845:Microinjections; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D018075:RNA, Complementary / Q000008:administration & dosage / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D013237:Stereoisomerism; D014982:Xenopus laevis; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
chemical_list: D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018075:RNA, Complementary; D018091:Receptors, AMPA; D026603:D-Aspartic Acid; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D007608:Kainic Acid