Characterization of Melatonin Receptors in the Rat Area postrema: Modulation of Affinity with Cations and Guanine Nucleotides
作者:
Jarmo T. Laitinen,
Gabriella Flügge,
Juan M. Saavedra,
期刊:
Neuroendocrinology
(Karger Available online 1990)
卷期:
Volume 51,
issue 6
页码: 619-624
ISSN:0028-3835
年代: 1990
DOI:10.1159/000125401
出版商: S. Karger AG
关键词: Affinity;Agonist binding;Circumventricular organs;G-proteins;2-[125I]iodomelatonin
数据来源: Karger
摘要:
We have localized and characterized the binding of the melatonin agonist, 2-[125I]iodomelatonin, in the rat area postrema (AP), by using quantitative autoradiography in vitro. At equilibrium conditions, Scatchard analysis revealed saturable high-affinity binding to a single class of sites (Ka 45.9 ± (SE) 6.0 pM and Bmax 30.8 ± 4.6 fmol/mg protein, n = 4 experiments with a total of 18 rats). Melatonin and 6-hydroxymelatonin were potent displacers of 2-[125I]iodomelatonin binding in the AP (IC50 20 and 500 pM, respectively) while N-acetylserotonin exhibited only a modest potency (IC50 25 nM). Micromolar concentrations of guanine nucleotides dose-dependently and specifically inhibited agonist binding at 22 ° C. Saturation studies revealed that this was due to a decrease in binding affinity. Divalent cations (4 mM CaCl2 or 2 mM MgCl2) had no detectable effect on the affinity of the binding site, whereas physiological concentrations of NaCl significantly decreased the binding affinity. These results demonstrate specific high-affinity binding sites for 2-[125I]iodomelatonin in the rat AP and suggest coupling of these putative receptors to guanosine nucleotide binding regulatory protein(
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