Molecular cloning and pharmacological characterization of a Bombyx mori tyramine receptor selectively coupled to intracellular calcium mobilization.
Tyramine (TA) is a biogenic amine in invertebrates. cDNA encoding the TA receptor (TAR) BmTAR2 was cloned from the nerve tissue of the silkworm Bombyx mori. The receptor's functional and pharmacological properties were examined in BmTAR2-transfected HEK-293 cells. In [(3)H]TA binding assays, BmTAR2 showed considerably higher affinity for TA than for other biogenic amines, with an IC(50) value of 57.5 nM. Moreover, TA induced a dose-dependent increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) in cells, with an EC(50) value of 11.6 nM, whereas octopamine and dopamine increased [Ca(2+)](i) only at concentrations above 100 microM. A few antagonists were found to inhibit the TA-induced increases in [Ca(2+)](i); the rank order of potency was yohimbine > chlorpromazine > mianserin. TA showed no effect on intracellular cAMP concentration. The data indicate that BmTAR2 belongs to the second class of TARs, which are selectively coupled to intracellular Ca(2+) mobilization. RT-PCR analysis revealed that BmTAR2 was expressed predominantly in the nervous tissue of B. mori larvae, suggesting that TA has neurotransmitter and neuromodulatory roles that are mediated by BmTAR2.
Huang
Jia
J
Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane, Japan.
Ohta
Hiroto
H
Inoue
Noriko
N
Takao
Haruka
H
Kita
Tomo
T
Ozoe
Fumiyo
F
Ozoe
Yoshihisa
Y
D000818:Animals; D001692:Biological Transport; D012831:Bombyx / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D006801:Humans; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D017982:Receptors, Biogenic Amine / Q000235:genetics* / Q000378:metabolism*; D014439:Tyramine / Q000378:metabolism
D019476:Insect Proteins; D017982:Receptors, Biogenic Amine; C066175:tyramine receptor; D002118:Calcium; D014439:Tyramine