Expression and pharmacological characterization of mouse metabotropic glutamate receptor subtype 5b

Metabotropic glutamate receptors (mGluRs) mediate many neuronal processes and represent attractive targets for pharmacologic intervention in various disease states. The Group I mGluR5 subtype and glutamatergic neurotransmission have been postulated to be involved in the pathophysiology of such CNS disorders as anxiety, depression, substance abuse or chronic pain. The mouse mGluR5b gene was cloned from mouse brain cDNA and expressed using an ecdysone‐inducible system. mGluR5b has an extra 96 bp sequence inserted in its cytoplasmic tail. mGluR5b cDNA was transfected into HEK‐293EcR cells pre‐expressing an ecdysone receptor. Receptor expression was induced with 10 μM ponasterone A (analogue of ecdysone) under conditions intended to avoid receptor desensitization. A FLIPR 384 ‐based calcium transient assay system was used to characterize the basic pharmacologic profile of a selected cell line. Quisqualic acid was the most potent agonist (EC 50 6.6 nM) with cells also responding to the endogenous ligand, L‐glutamic acid, as well as another Group I‐selective agonist, 3,5‐DHPG. Similarly, calcium transient stimulation by all three agonists was potently inhibited by reference mGluR5 antagonists – MPEP, MTEP and methoxy‐PEPy (IC 50 ’s <0.1 – 36 nM). The availability of this mouse mGluR5b‐expressing cell line will facilitate in vitro characterization of therapeutic agents prior to in vivo testing.