Molecular and pharmacological analysis of an octopamine receptor from American cockroach and fruit fly in response to plant essential oils

Octopamine receptors from American cockroach, Periplaneta americana (Pa oa1), and fruit fly, Drosophila melanogaster (OAMB), were cloned and permanently expressed in HEK-293 cells, and found to activate adenylate cyclase activity and increase [Ca2+]i levels through G-protein coupled receptor signaling pathways. Sequencing information (GenBank accession number AY333178) and functional data of Pa oa1 were recently published. Saturation binding analysis with 3H-yohimbine was performed with Pa oa(1) and OAMB expressed in COS-7 cells. The K(d) values were determined to be 28.4 and 43.0 nM, respectively. B(max) was determined to be 11.8 and 8.04 pmol receptor/mg protein, respectively. Competitive binding data using cell membranes expressing either OAMB or Pa oa1 demonstrated significantly decreased binding activity in binding assays performed in the presence of plant essential oils, eugenol, cinnamic alcohol, and trans-anethole. Eugenol decreased cAMP level in HEK-293 cells expressing Pa oa1, but trans-anethole increased cAMP in HEK-293 cells expressing OAMB. All three chemicals increased [Ca2+]i level in both cell models. Toxicity data against fruit flies and American cockroaches demonstrated species differences in response to treatment with tested plant essential oils. The toxicity of tested chemicals against wild type and octopamine mutant (iav) fly strains suggested that an octopamine receptor mediates the toxicity of cinnamic alcohol, eugenol, trans-antehole, and 2-phenethyl propionate against fruit flies. Collectively, the data suggest a correlation between cellular changes induced by tested plant essential oils and their toxicity against fruit fly and American cockroach.