Inducible expression and pharmacological characterization of the mouse metabotropic glutamate 5b receptor.

The metabotropic glutamate receptor subtype 5 (mGlu5) and glutamatergic neurotransmission are associated with the pathophysiology of disorders such as anxiety, depression or chronic pain. Human and rat mGlu5 receptors have been cloned and characterized previously. We now describe the cloning of the mouse mGlu5b receptor gene from adult mouse brain and its expression using an ecdysone-inducible system. This subtype has an extra 96 bp sequence which is inserted to the cytoplasmic tail and is identical to the insert present in human and rat mGlu5b. Mouse mGlu5b receptor expression was induced in HEK-293EcR cells by incubation with ponasterone A, an analogue of the insect hormone ecdysone. A fluorometric calcium transient assay system was used to characterize the basic pharmacologic profile of an isolated stable cell line. Quisqualic acid was the most potent receptor agonist (EC(50) approximately 7 nM) although the cells also responded to l-glutamic acid and the Group I-selective receptor agonist, 3,5-dihydroxyphenylglycine (3,5-DHPG). The calcium transients stimulated by these agonists were potently inhibited by reference allosteric mGlu5 antagonists - 2-methyl-6-(phenylethynyl)pyridine (MPEP), 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) and 3-methoxy-5-(pyridine-2-ylethynyl)pyridine (methoxy-PEPy) (IC(50) ranges: 0.8-66 nM). The availability of this mouse mGlu5b receptor-expressing cell line will facilitate in vitro characterization of mGlu5 receptor-selective agonists or antagonists prior to in vivo pharmacologic testing.