Methods for vapor detection and discrimination with mammalian odorant receptors expressed in heterologous cells

A method of identifying an odorant receptor ligand comprising the steps of:

• a) providing a biological sample comprising cells expressing at least one odorant receptor and exposing the biological sample to at least one test compound in a vapor/gaseous phase,
• wherein the one or more odorant receptors at least includes olfr145,
• wherein the biological sample further expresses at least one of the following:
• one or more proteins known to enhance cell surface localization of the odorant receptors selected from REEP1, RTP1 and RTP2,
• one or more odorant receptor binding proteins selected from Lcn3, Lcn4, Lcn10, Lcn11, OBP1a, OBP1b, and OBP2b, and
• one or more metabolic enzymes, wherein the one or more metabolic enzymes at least includes carboxyl esterase;
• b) measuring a signal that is proportional to activation of one of the odorant receptors in said biological sample, and
• c) comparing the measured level of activation of one of the odorant receptors determined in step b) to a reference activation level for the specific odorant receptor determined in the same conditions with a negative control where the biological sample has not been exposed to said at least one test compound in a vapor/gaseous phase.