Functional and pharmacological characterization of a beta-adrenergic-like octopamine receptor from the silkworm Bombyx mori.
A cDNA encoding a seven-transmembrane receptor was cloned from the nervous tissues of silkworm (Bombyx mori) larvae. Sequence analysis indicated that the gene is an ortholog of CG6989, which encodes a Drosophila beta-adrenergic-like octopamine (OA) receptor (DmOct beta 2R). As very little information is available regarding this class of receptors, we generated a cell line that stably expressed the gene in HEK-293 cells and we then performed functional and pharmacological studies of this receptor. [(3)H]OA-binding assays using membrane preparations of this cell line showed that the receptor possesses a higher affinity for OA than for tyramine (TA) or dopamine (DA). The cell line elicited a bell-shaped, OA concentration-dependent increase in intracellular cAMP levels, with a maximum at 100 nM. (R)-OA was more potent than (S)-OA. TA and DA had weak or marginal effects on cAMP production. The OA receptor agonist demethylchlordimeform elicited a similar biphasic response, although the maximum response was attained at a concentration as low as 1 nM. The rank order of potency of other agonists was as follows: naphazoline > tolazoline, clonidine. Among the antagonists tested, only chlorpromazine significantly attenuated the OA-induced increase in cAMP levels. No increase in intracellular Ca(2+) levels was observed with OA at concentrations up to 100 microM. These findings indicate that the cloned receptor is a beta-adrenergic-like OA receptor with unique functional and pharmacological properties.
Chen
Xi
X
Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan.
Ohta
Hiroto
H
Ozoe
Fumiyo
F
Miyazawa
Kazuya
K
Huang
Jia
J
Ozoe
Yoshihisa
Y
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D012831:Bombyx / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry; D006801:Humans; D019476:Insect Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D008969:Molecular Sequence Data; D009655:Octopamine / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D017982:Receptors, Biogenic Amine / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D016415:Sequence Alignment
D018076:DNA, Complementary; D019476:Insect Proteins; D011943:Receptors, Adrenergic, beta; D017982:Receptors, Biogenic Amine; C027604:norsynephrine receptor; D009655:Octopamine