A [S-35] GTP-GAMMA-S BINDING ASSESSMENT OF METABOTROPIC GLUTAMATE-RECEPTOR STANDARDS IN CHINESE-HAMSTER OVARY CELL-LINES EXPRESSING THE HUMAN METABOTROPIC RECEPTOR SUBTYPE-2 AND SUBTYPE-4

The activities of metabotropic glutamate receptor (mGluR) standards we re evaluated in the [S-35]GTP gamma S binding assay and in the forskol in (FSK)-enhanced cyclic AMP assay using Chinese hamster ovary (CHO) c ells or homogenates which expressed the human mGluR (hmGluR) subtypes 2 and 4. Though distinct rank orders of activities were determined for the agonists between the cell lines expressing individual hmGluRs, si milar rank orders of agonist activities were determined for the standa rds between assays. O-phospho-L-serine (L-SOP) and (S)-2-amino-2-methy l-4-phosphonobulanoic acid (MAP4) antagonized agonist EC90 responses i n the cell Lines expressing the hmGluR 2 and 4 subtypes, respectively. In addition to its antagonist effect, L-SOP increased the baseline le vel of cAMP when tested in the absence of agonist. In spite of this an omalous effect, L-SOP was found to be a competitive antagonist in the cAMP assay as well as in the [S-35]GTP gamma S binding assay with a pA (2) value of 5.2 in both assays. MAP4 was a competitive antagonist of L(+)-2-amino-4-phosphonobutyric acid (L-AP4)-induced responses in the CHO cell line expressing hmGluR4 with pA(2) values of 4.4 and 4.5 dete rmined in the [S-35]GTP gamma S binding and cAMP assays, respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.