title: AmTAR2: Functional characterization of a honeybee tyramine receptor stimulating adenylyl cyclase activity.
abstract: The biogenic monoamines norepinephrine and epinephrine regulate important physiological functions in vertebrates. Insects such as honeybees do not synthesize these neuroactive substances. Instead, they employ octopamine and tyramine for comparable physiological functions. These biogenic amines activate specific guanine nucleotide-binding (G) protein-coupled receptors (GPCRs). Based on pharmacological data obtained on heterologously expressed receptors, α- and β-adrenergic-like octopamine receptors are better activated by octopamine than by tyramine. Conversely, GPCRs forming the type 1 tyramine receptor clade (synonymous to octopamine/tyramine receptors) are better activated by tyramine than by octopamine. More recently, receptors were characterized which are almost exclusively activated by tyramine, thus forming an independent type 2 tyramine receptor clade. Functionally, type 1 tyramine receptors inhibit adenylyl cyclase activity, leading to a decrease in intracellular cAMP concentration ([cAMP]i). Type 2 tyramine receptors can mediate Ca2+signals or both Ca2+signals and effects on [cAMP]i. We here provide evidence that the honeybee tyramine receptor 2 (AmTAR2), when heterologously expressed in flpTM cells, exclusively causes an increase in [cAMP]i. The receptor displays a pronounced preference for tyramine over octopamine. Its activity can be blocked by a series of established antagonists, of which mianserin and yohimbine are most efficient. The functional characterization of two tyramine receptors from the honeybee, AmTAR1 (previously named AmTYR1) and AmTAR2, which respond to tyramine by changing cAMP levels in opposite direction, is an important step towards understanding the actions of tyramine in honeybee behavior and physiology, particularly in comparison to the effects of octopamine.
authors.affiliation: Institute of Biochemistry and Biology, University of Potsdam, Potsdam, Germany.
authors.forename: Tina
authors.initials: T
authors.lastname: Reim
authors.affiliation: Institute of Complex Systems, ICS-4, Forschungszentrum Jülich, Jülich, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Balfanz
authors.affiliation: Institute of Complex Systems, ICS-4, Forschungszentrum Jülich, Jülich, Germany.
authors.forename: Arnd
authors.initials: A
authors.lastname: Baumann
authors.affiliation: Zoological Institute, University of Cologne, Cologne, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Blenau
authors.affiliation: Institute of Biochemistry and Biology, University of Potsdam, Potsdam, Germany; Behavioral Physiology and Sociobiology (Zoology II), Biocenter, University of Würzburg, Würzburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Thamm
authors.affiliation: Institute of Biochemistry and Biology, University of Potsdam, Potsdam, Germany; Behavioral Physiology and Sociobiology (Zoology II), Biocenter, University of Würzburg, Würzburg, Germany. Electronic address: ricarda.scheiner@uni-wuerzburg.de.
authors.forename: Ricarda
authors.initials: R
authors.lastname: Scheiner
mesh_terms: D000262:Adenylyl Cyclases / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001516:Bees / Q000235:genetics* / Q000378:metabolism; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D009655:Octopamine / Q000378:metabolism; D010802:Phylogeny; D017982:Receptors, Biogenic Amine / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D015398:Signal Transduction
chemical_list: D019476:Insect Proteins; D017982:Receptors, Biogenic Amine; C066175:tyramine receptor; D009655:Octopamine; D000262:Adenylyl Cyclases
keywords: Behavior; Biogenic amines; Cellular signaling; GPCR; Honeybee; Second messenger