Direct radiolabeling by [H-3]quisqualic acid of group I metabotropic glutamate receptor in rat brain synaptic membranes

[H-3]Quisqualic acid (QA) was synthesized and used to label metabotropic gl utamate receptor (mGluR) in rat brain synaptic membranes in the presence of three different ionotropic glutamate receptor agonists at respective satur ating concentrations. Of several mGluR agonists tested, group I agonists we re more potent in displacing [H-3]QA binding than group II and group III ag onists in the presence of the three ionotropic agonists. [H-3]QA binding wa s markedly inhibited by guanine nucleotide analogues in a concentration-dep endent manner at a concentration range of 10 nM to 1 mM. Scatchard analysis revealed that [H-3]QA binding consisted of a single component with a K-d o f 50.9+/-5.3 nM and a B-max of 431.6+/-18.3 fmol/mg protein. These results suggest that [H-3]QA indeed labels group I mGluR functionally coupled to GT P binding protein in rat brain synaptic membranes when determined under the experimental conditions employed. (C) 2000 Elsevier Science B.V. All right s reserved.