Description:
The catecholamines norepinephrine and epinephrine are important regulators ofvertebrate physiology. Insects such as honeybees do not synthesize these neuroactive substances.Instead, they use the phenolamines tyramine and octopamine for similar physiological functions.These biogenic amines activate specific members of the large protein family of G protein-coupledreceptors (GPCRs). Based on molecular and pharmacological data, insect octopamine receptorswere classified as either - or -adrenergic-like octopamine receptors. Currently, one - and four-receptors have been molecularly and pharmacologically characterized in the honeybee. Recently,an 2-adrenergic-like octopamine receptor was identified in Drosophila melanogaster (DmOct2R).This receptor is activated by octopamine and other biogenic amines and causes a decrease inintracellular cAMP ([cAMP]i). Here, we show that the orthologous receptor of the honeybee(AmOct2R), phylogenetically groups in a clade closely related to human 2-adrenergic receptors.When heterologously expressed in an eukaryotic cell line, AmOct2R causes a decrease in [cAMP]i.The receptor displays a pronounced preference for octopamine over tyramine. In contrast toDmOct2R, the honeybee receptor is not activated by serotonin. Its activity can be blocked ecientlyby 5-carboxamidotryptamine and phentolamine. The functional characterization of AmOct2R nowadds a sixth member to this subfamily of monoaminergic receptors in the honeybee and is an importantstep towards understanding the actions of octopamine in honeybee behavior and physiology.