Elsevier

Neuropharmacology

Volume 36, Issues 11–12, November–December 1997, Pages 1483-1488
Neuropharmacology

A novel kainate receptor ligand [3H]-(2S,4R)-4-methylglutamate: Pharmacological characterization in rabbit brain membranes

https://doi.org/10.1016/S0028-3908(97)00161-5Get rights and content

Abstract

Since kainate evokes large non-desensitizing currents at α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, kainate is of limited use in discriminating between AMPA and kainate receptors. Following recent reports that (2S,4R)-4-methylglutamate is a kainate receptor-selective agonist, we have radiolabelled and subsequently characterized the binding of [3H]-(2S,4R)-4-methylglutamate to rabbit whole-brain membranes. [3H]-(2S,4R)-4-methylglutamate binding was rapid, reversible and labelled two sites (KD1 = 3.67 ± 0.50 nM/Bmax1 = 0.54 ± 0.03 pmol/mg protein and KD2 = 281.66 ± 12.33 nM/ Bmax2 = 1.77 ± 0.09 pmol/mg protein). [3H]-(2S,4R)-4-methylglutamate binding was displaced by several non-NMDA receptor ligands: domoate > kainate ⪢ l-quisqualate ⩾ l-glutamate > 6-cyano-7-nitroquinoxaline-2, 3-dione (CNQX) ⪢ (S)-AMPA = (S)-5-fluorowillardiine > NMDA. Neither the metabotropic glutamate receptor agonists (1S,3R)-ACPD or l-AP4, together with the l-glutamate uptake inhibitor l-trans-2,4-PDC, influenced binding when tested at 100 μM. We conclude that [3H]-(2S,4R)-4-methylglutamate is a useful radioligand for labelling kainate receptors. It possesses high selectivity, and possesses a pharmacology similar to that for rat cloned low-affinity (Glu5 and 6) kainate receptor subunits.

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