title: Binding of the new radioligand (S)-[3H]AMPA to rat brain synaptic membranes: effects of a series of structural analogues of the non-NMDA receptor agonist willardiine.
abstract: This study examined the binding of (S)-[3H]AMPA, the radiolabelled active isomer of AMPA, to rat brain synaptic membranes. Under non-chaotropic conditions specific binding of 10 nM (S)-[3H]AMPA represented 33 +/- 2% of the total; this increased to 74 +/- 1% in the presence of 100 mM KSCN. (S)-[3H]AMPA binding was inhibited by non-NMDA receptor agonists and the antagonists NBQX and CNQX, with the following rank order of potency: NBQX > (S)-AMPA > or = quisqualate > CNQX > L-glutamate > domoate > or = kainate > (R)-AMPA. NMDA, and the metabotropic glutamate receptor agonist (1S,3R)-ACPD, up to 100 microM, did not inhibit (S)-[3H]AMPA binding. A number of willardiine analogues all effectively inhibited (S)-[3H]AMPA binding with the rank order of potency: (S)-5-fluorowillardiine > (S)-5-nitrowillardiine > (S)-5-trifluoromethylwillardiine > (S)-5-bromowillardiine approximately (S)-5-chlorowillardiine > (S)-5-cyanowillardiine > (S)-willardiine > (S)-5-iodowillardiine > (S)-6-methylwillardiine > (S)-5-methylwillardiine. This rank order closely reflects data from equilibrium measurements made, under voltage clamp, on cultured hippocampal neurons. In contrast the respective (R)-enantiomers and the racemate mixtures of (R,S)-3, 5 and 6-isowillardiine were relatively inactive. Similar IC50 values and thus rank orders of potency for the willardiines were observed in the presence of 100 mM KSCN.
authors.affiliation: Department of Pharmacology, University of Bristol, Langford, U.K.
authors.forename: L M
authors.initials: LM
authors.lastname: Hawkins
authors.forename: K M
authors.initials: KM
authors.lastname: Beaver
authors.forename: D E
authors.initials: DE
authors.lastname: Jane
authors.forename: P M
authors.initials: PM
authors.lastname: Taylor
authors.forename: D C
authors.initials: DC
authors.lastname: Sunter
authors.forename: P J
authors.initials: PJ
authors.lastname: Roberts
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000409:Alanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000648:ultrastructure; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D011744:Pyrimidinones; D011810:Quinoxalines / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000187:drug effects; D013237:Stereoisomerism; D013570:Synaptic Membranes / Q000378:metabolism*; D014316:Tritium; D014498:Uracil; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000378:metabolism*
chemical_list: C000591839:5-nitrowillardiine; D011744:Pyrimidinones; D011810:Quinoxalines; D018091:Receptors, AMPA; D003515:Cycloleucine; D014316:Tritium; C036361:1-amino-1,3-dicarboxycyclopentane; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C002872:willardiine; D014498:Uracil; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D000409:Alanine