title: 2-[125I]iodomelatonin binding sites in the bovine hippocampus are not sensitive to guanine nucleotides.
abstract: The discrete distribution and pharmacological characteristics of melatonin binding sites in the bovine hippocampus were determined. Autoradiography revealed the presence of melatonin binding sites in the stratum lacunosum-molecularis of the hippocampus (CA1), stratum molecularis of the subiculum and in the enthorhinal cortex. Analysis of the kinetic parameters demonstrated that the binding was stable and reversible, represented by a single class high affinity binding sites (Kd 40 pM, Bmax = 3.9 fmol/mg protein). However, 2-iodomelatonin and 2-bromomelatonin inhibited 2-[125I]iodomelatonin binding in a biphasic manner. The presence of 4 mM CaCl2 did not cause changes in the affinity constant values. Finally, experiments performed with GTP gamma S revealed that binding affinity was not decreased even with high concentrations of the nucleotide. These findings show that 2-[125I]iodomelatonin binding sites in the bovine parahippocampal-hippocampal region possess some binding features not common to melatonin receptors described so far; moreover they seem not to be linked to a regulatory G-protein.
mesh_terms: D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D005260:Female; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects*; D007700:Kinetics; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D006150:Guanine Nucleotides; C044556:2-iodomelatonin; D008550:Melatonin