Pharmacological characterization of a Bombyx mori α‐adrenergic‐like octopamine receptor stably expressed in a mammalian cell line

Series of agonists and antagonists were examined for their actions on a Bombyx mori α‐adrenergic‐like octopamine receptor (OAR) stably expressed in HEK‐293 cells. The rank order of potency of the agonists was clonidine>naphazoline>tolazoline in Ca 2+ mobilization assays, and that of the antagonists was chlorpromazine>yohimbine. These findings suggest that the B. mori OAR is more closely related to the class‐1 OAR in the intact tissue than to the other classes. N ′‐(4‐Chloro‐ o ‐tolyl)‐ N ‐methylformamidine (DMCDM) and 2‐(2,6‐diethylphenylimino)imidazolidine (NC‐5) elevated the intracellular calcium concentration ([Ca 2+ ] i ) with EC 50 s of 92.8 µM and 15.2 nM, respectively. DMCDM and NC‐5 led to increases in intracellular cAMP concentration ([cAMP] i ) with EC 50 s of 234 nM and 125 nM, respectively. The difference in DMCDM potencies between the cAMP and Ca 2+ assays might be due to “functional selectivity.” The Ca 2+ and cAMP assay results for DMCDM suggest that the elevation of [cAMP] i , but not that of [Ca 2+ ] i , might account for the insecticidal effect of formamidine insecticides. © 2009 Wiley Periodicals, Inc.