Odorant responsiveness of a mouse olfactory receptor, mOR-EG, was investigated in various heterologous cells using a variety of detection methods. Odorant-induced Ca2+ response was observed in HEK293 cells that coexpressed mOR-EG and the promiscuous G protein, Galpha15. Without Galpha15, a robust increase in cAMP level was observed upon odorant-stimulation in various mammalian cells. A luciferase reporter gene assay using zif268 promoter was adopted to amplify the cAMP signals. In Xenopus laeVis oocytes, odorant-stimulated currents were recorded when mOR-EG cRNA was co-injected with either Galpha15 or cAMP-dependent channel. These results suggest that odorant responsiveness can be monitored via a signaling pathway mediated by endogenous Galphas or transfected Galpha15 in heterologous cell systems. Various functional assays for a heterologously expressed olfactory receptor reported in this study, are potentially useful for high-throughput ligand screening and functional analyses of hundreds of olfactory receptors. (C) 2003 Elsevier Science (USA). All rights reserved.