Antagonist properties of a phosphono isoxazole amino acid at glutamate R1-4 (R,S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid receptor subtypes.
The activity of the (R, S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptor antagonist, (R,S) -2-amino-3-[5-tert-butyl-3-(phosphonomethoxy)-4-isoxazolyl] propionic acid (ATPO), at recombinant ionotropic glutamate receptors (GluRs) was evaluated using electrophysiological techniques. Responses at homo- or heterooligomeric AMPA-preferring GluRs expressed in human embryonic kidney (HEK) 293 cells (GluR1-flip) or Xenopus laevis oocytes (GluR1-4-flop or GluR1-flop + GluR2) were potently inhibited by ATPO with apparent dissociation constants (Kb values) ranging from 3.9 to 26 microM. A Schild analysis for kainate (KA)-activated GluR1 receptors showed ATPO to have a KB of 8.2 microM and a slope of unity, indicating competitive inhibition. The antagonism by ATPO at GluR1 was of similar magnitude at holding potentials between -100 mV and +20 mV. In contrast, ATPO (<300 microM), does not inhibit responses to kainate at homomeric GluR6 or heterooligomeric GluR6/KA2 expressed in HEK 293 cells but activated GluR5 and GluR5/KA2 expressed in X. laevis oocytes. ATPO produced <15% inhibition at the maximal concentration (300 microM) of current responses through NR1A + NR2B receptors expressed in X. laevis oocytes. Thus, ATPO shows a unique pharmacological profile, being an antagonist at GluR1-4 and a weak partial agonist at GluR5 and GluR5/KA2.
Wahl
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P
Department of Molecular Pharmacology, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Maaloev, Denmark. pwa@novo.dk
Anker
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C
Traynelis
S F
SF
Egebjerg
J
J
Rasmussen
J S
JS
Krogsgaard-Larsen
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P
Madsen
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U
D000818:Animals; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007555:Isoxazoles / Q000494:pharmacology*; D063065:Organophosphonates / Q000494:pharmacology*; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors; D014982:Xenopus laevis
C111046:2-amino-3-(5-tert-butyl-3-(phosphonomethoxy)-4-isoxazolyl)propionic acid; D018691:Excitatory Amino Acid Antagonists; D007555:Isoxazoles; D063065:Organophosphonates; D018091:Receptors, AMPA; D011994:Recombinant Proteins