title: Differential sensitivity to cations of the melatonin receptors in the rat area postrema and suprachiasmatic nuclei.
abstract: We studied the effects of cations on the binding of the melatonin (MT) agonist, 125I-MT, to MT receptors in the rat area postrema (AP) and suprachiasmatic nuclei (SCN), by using quantitative autoradiography in vitro. Ca2+ promoted agonist binding in the SCN but was without effect in the AP. Na+ induced a dose-dependent loss of agonist binding in both areas. This effect was more drastic in the SCN and also in the absence of divalent cations. The presence of 0.1-4.0 mM Ca2+ or Mg2+ partially and nonselectively reversed this Na(+)-elicited inhibition. The data agree with known cationic effects on agonist binding to other G protein-coupled receptors and deepen our understanding of the mammalian MT receptor.
authors.affiliation: Section on Pharmacology, National Institute of Mental Health, Bethesda, Maryland 20892.
authors.forename: J T
authors.initials: JT
authors.lastname: Laitinen
authors.forename: J M
authors.initials: JM
authors.lastname: Saavedra
mesh_terms: D000818:Animals; D001345:Autoradiography; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D002552:Cerebral Ventricles / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D007457:Iodine Radioisotopes; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats; D011919:Rats, Inbred Strains; D044094:Receptors, Melatonin; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D013493:Suprachiasmatic Nucleus / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D007457:Iodine Radioisotopes; D044094:Receptors, Melatonin; D017981:Receptors, Neurotransmitter; D012965:Sodium Chloride; D008274:Magnesium; D008550:Melatonin; D002794:Choline; D002118:Calcium