TY - JOUR T1 - A Novel Assay of G<sub>i/o</sub>-Linked G Protein-Coupled Receptor Coupling to Potassium Channels Provides New Insights into the Pharmacology of the Group III Metabotropic Glutamate Receptors JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1213 LP - 1224 DO - 10.1124/mol.107.041053 VL - 73 IS - 4 AU - Colleen M. Niswender AU - Kari A. Johnson AU - Qingwei Luo AU - Jennifer E. Ayala AU - Caroline Kim AU - P. Jeffrey Conn AU - C. David Weaver Y1 - 2008/04/01 UR - http://molpharm.aspetjournals.org/content/73/4/1213.abstract N2 - The group III metabotropic glutamate receptors (mGluRs) represent a family of presynaptically expressed G-protein-coupled receptors (GPCRs) with enormous therapeutic potential; however, robust cellular assays to study their function have been difficult to develop. We present here a new assay, compatible with traditional high-throughput screening platforms, to detect activity of pharmacological ligands interacting with Gi/o-coupled GPCRs, including the group III mGluRs 4, 7, and 8. The assay takes advantage of the ability of the Gβγ subunits of Gi and Go heterotrimers to interact with G-protein regulated inwardly rectifying potassium channels (GIRKs), and we show here that we are able to detect the activity of multiple types of pharmacophores including agonists, antagonists, and allosteric modulators of several distinct GPCRs. Using GIRK-mediated thallium flux, we perform a side-by-side comparison of the activity of a number of commercially available compounds, some of which have not been extensively evaluated because of the previous lack of robust assays at each of the three major group III mGluRs. It is noteworthy that several compounds previously considered to be general group III mGluR antagonists have very weak activity using this assay, suggesting the possibility that these compounds may not effectively inhibit these receptors in native systems. We anticipate that the GIRK-mediated thallium flux strategy will provide a novel tool to advance the study of Gi/o-coupled GPCR biology and promote ligand discovery and characterization. The American Society for Pharmacology and Experimental Therapeutics ER -