Enhancement of agonist binding to 5-HT1A receptors in rat brain membranes by millimolar Mn2+.
Manganese in millimolar concentration caused increase in specific binding of [(3)H]8-OH-DPAT to rat hippocampal membranes up to 44% in comparison with experiments in the presence of Mg(2+), while no significant differences were found in rat cortical membranes. Similar increase in high-affinity agonist binding sites by Mn(2+) was found in displacement curves of 8-OH-DPAT, where antagonist [(3)H]WAY100635 was used as reporter ligand. The removal of bivalent ions with EDTA caused full loss of high-affinity binding of agonists, but not for antagonists. Therefore it was hypothesized, that the effect of Mn(2+)- and Mg(2+)-ions was modulated through their action on different G-proteins. Results showed that efficient coupling of G-protein and 5-HT(1A) receptors is crucial to modify Mg(2+) and Mn(2+) effects, whereas Mn(2+) is more potent stabilizer of agonist high-affinity binding, especially when GTPgammaS is present. Using Sf9 cells as model system, we have shown that G(i1) proteins are required to modulate Mn(2+)-dependent high-affinity agonist binding to 5-HT(1A) receptors, but further studies are necessary to find the cofactors of Mn(2+) modulation to signal transduction.
Institute of Chemistry, University of Tartu, Jakobi 2, Tartu, Estonia.
Sven
S
Parkel
Johnny
J
Näsman
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D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D008345:Manganese / Q000008:administration & dosage*; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D044282:Receptor, Serotonin, 5-HT1A / Q000378:metabolism*; D017366:Serotonin Receptor Agonists / Q000378:metabolism*
D017366:Serotonin Receptor Agonists; D044282:Receptor, Serotonin, 5-HT1A; D008345:Manganese