LIGAND-BINDING PROFILE OF THE RAT METABOTROPIC GLUTAMATE-RECEPTOR MGLUR3 EXPRESSED IN A TRANSFECTED CELL-LINE

A cDNA clone encoding the rat metabotropic glutamate receptor mGluR3 w as stably transfected into human embryonic kidney 293 cells. Receptor- expressing cell lines were characterized by centrifugation binding ass ays using [H-3]glutamate as radioligand. The rank order of affinity wa s amate>(1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) >L(+)-2-amino-3-phosphonopropionic acid (L-AP3)>quisqualic acid>L(+)-2 -amino-4-phosphonobutyric acid (L-AP4)>ibotenic acid. The active enant iomers of several phenylglycines displayed K-i values of 300 to 400 mu M. The nonactive enantiomers and the standard ionotropic glutamate re ceptor ligands N-methyl-D-aspartic acid (NMDA), lpha-amino-3-hydroxy-5 -methyl-4-isoxazolepropionic acid (AMPA) and kainic acid only weakly d isplaced [H-3]glutamate. In this cell line, L-glutamate and (2S,3S,4S) -alpha-(Carboxycyclopropyl)-glycine (L-CCG-I) reduced cAMP levels in a dose-dependent manner. The sensitivity of this system and its easy ap plicability make it feasible to envisage ligand binding assays on cell lines expressing cloned receptors as useful screening tools to discov er and characterize new and specific agonists and antagonists.