title: Alpha-[3H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding to human cerebral cortical membranes: minimal changes in postmortem brains of chronic schizophrenics.
abstract: The binding of alpha-[3H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA), a selective ligand for the ion channel-linked quisqualate receptor, was evaluated in Triton X-100-treated membranes of human cerebral cortex. The presence of chaotropic ions produced divergent effects on specific [3H]AMPA binding: A twofold increase in the binding was observed with thiocyanide at 100 mM, although iodide (100 mM) and perchlorate (100 mM) reduced the binding. Chemical modifications of the sulfhydryl group with p-chloromercuriphenylsulfonic acid (PCMBS) produced threefold increases in specific [3H]-AMPA binding in the absence of KSCN as well as in the presence of KSCN. Treatment with dithiothreitol restored the enhanced specific [3H]AMPA binding by PCMBS to the basal level. Although specific [3H]AMPA binding in the absence of KSCN showed a single site (KD = 220 nM, Bmax = 235 fmol/mg of protein), curvilinear Scatchard plots of specific [3H]AMPA binding in the presence of 100 mM KSCN can be resolved into two binding sites with the following parameters: KD1 = 5.82 nM, Bmax1 = 247 fmol/mg of protein; KD2 = 214 nM, Bmax2 = 424 fmol/mg of protein. Quisqualate and AMPA were the most potent inhibitors of the [3H]AMPA binding in the presence of KSCN. Potent inhibitors of the binding included beta-N-oxalylamino-L-alanine (L-BOAA), cysteine-S-sulfate, L-glutamate, 6-cyano-7-nitroquinoxaline-2,3-dione, and 6,7-dinitroquinoxaline-2,3-dione. Kainate, L-homocysteine sulfinic acid, and L-homocysteic acid were active with an IC50 value of a micromolar concentration, whereas L-cysteic acid and L-cysteine sulfinic acid were weakly active.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Neuropsychiatry, Tokyo Medical and Dental University, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Kurumaji
authors.forename: M
authors.initials: M
authors.lastname: Ishimaru
authors.forename: M
authors.initials: M
authors.lastname: Toru
mesh_terms: D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000328:Adult; D000368:Aged; D001921:Brain / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D002908:Chronic Disease; D005260:Female; D006801:Humans; D007051:Ibotenic Acid / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D008566:Membranes / Q000378:metabolism; D008875:Middle Aged; D012016:Reference Values; D012559:Schizophrenia / Q000378:metabolism*; D014018:Tissue Distribution; D014316:Tritium; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid
chemical_list: D014316:Tritium; D007051:Ibotenic Acid; D002731:4-Chloromercuribenzenesulfonate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid