title: Characterization of melatonin binding sites in the brain and retina of the frog Rana perezi.
abstract: The aim of this study was to characterize 2-[125I]iodomelatonin binding sites in the neural retina and central nervous system (telencephalon, diencephalon, and optic tectum) of the anuran amphibian Rana perezi. Saturation and kinetic studies and pharmacological characterization revealed the existence of a unique melatonin-binding site that belongs to the Mel 1 receptor subtype. The affinity of this site is similar in all tissues studied (Kd, 10.5-12.8 pM), but the density varied from diencephalon and optic tectum, which exhibit the highest density, to telencephalon with the lowest. Neural retina showed an intermediate receptor density. This melatonin-binding site fulfills the requirements of a real hormone receptor; the binding is saturable, reversible, and inhibited by different melatonin agonists and antagonists. The affinity order of ligands is: 2-phenyl-melatonin = 2-I-melatonin > 6-Cl-melatonin = melatoninz >> luzindole. Additionally, specific binding is decreased by non-hydrolysable GTP analogue, sodium, and by pretreatment of membranes with pertussis toxin. All these results suggest the existence of a widely distributed and pharmacologically homogeneous melatonin receptor of the subfamily Mel 1 in the nervous system of Rana perezi coupled to a Gi/o protein.
authors.affiliation: Departamento de Fisiología (Fisiología Animal II), Facultad de Biología, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: Esther
authors.initials: E
authors.lastname: Isorna
authors.forename: Ana
authors.initials: A
authors.lastname: Guijarro
authors.forename: María Jesús
authors.initials: MJ
authors.lastname: Delgado
authors.forename: Mercedes
authors.initials: M
authors.lastname: Alonso-Bedate
authors.forename: Angel L
authors.initials: AL
authors.lastname: Alonso-Gómez
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004027:Diencephalon / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008550:Melatonin / Q000031:analogs & derivatives* / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D011869:Radioligand Assay; D011898:Ranidae; D044094:Receptors, Melatonin / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism; D013477:Superior Colliculi / Q000378:metabolism; D013687:Telencephalon / Q000378:metabolism; D013764:Tetrahydronaphthalenes / Q000378:metabolism; D014363:Tryptamines / Q000378:metabolism
chemical_list: C100536:2-phenylmelatonin; C114459:4-phenyl-2-propionamidotetraline; D044094:Receptors, Melatonin; D013764:Tetrahydronaphthalenes; D014363:Tryptamines; C057154:luzindole; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C024100:6-chloromelatonin; C044556:2-iodomelatonin; D012964:Sodium; D037342:Pertussis Toxin; D008274:Magnesium; D008550:Melatonin