Functional Characterization of Dopamine and Neuropeptide G Protein-Coupled Receptors from the Silkworm Bombyx mori By Aequorin Bioluminescence-Based Calcium Assay

Biogenic amines and neuropeptides act as neurotransmitters, neuromodulators, and neurohormones in insects. Their receptors belong to the G protein-coupled receptor (GPCR) family and have potential as insect pest control targets. In the present study, three Bombyx mori dopamine (DA) receptors, BmDopR13, and the B. mori ecdysis-triggering hormone receptor (BmETHR) were examined for their ability to increase intracellular Ca2+ levels using an aequorin bioluminescence-based calcium assay. When BmDopR1-3 were expressed separately in HEK-293 cells, only BmDopR2 induced Ca2+-dependent luminescence in a DA concentration-dependent manner. BmDopR1 and BmDopR3 showed almost no response to DA. The typical agonist, 6,7-ADTN, and antagonist, flupenthixol, were highly effective for BmDopR2. Interestingly, the octopamine receptor agonist demethylchlordimeform was found to act on BmDopR2 as an antagonist, suggesting that BmDopR2 has a unique pharmacological profile. Functional analysis of BmETHR showed a BmETH dose-dependent Ca2+ response. The present aequorin assay system is convenient and simple; it should be also useful for screening a lead of insecticides or insectistatics targeting Ca2+ mobilization-related biogenic amine and neuropeptide GPCRs such as BmDopR2 and BmETHR.