title: S1P-receptors in PC12 and transfected HEK293 cells: molecular targets of hypotensive imidazoline I(1) receptor ligands.
abstract: The present study aimed at elucidating the molecular identity of the proposed "I(1)-imidazoline receptors", i.e. non-adrenoceptor recognition sites via which the centrally acting imidazolines clonidine and moxonidine mediate a major part of their effects. In radioligand binding experiments with [(3)H]clonidine and [(3)H]lysophosphatidic acid on intact, alpha(2)-adrenoceptor-deficient PC12 cells, moxonidine, clonidine, lysophosphatidic acid and sphingosine-1-phosphate (S1P) competed for the specific binding sites of both radioligands with similar affinities. RNA interference with the rat S1P(1)-, S1P(2)- or S1P(3)-receptor abolished specific [(3)H]lysophosphatidic acid binding. [(3)H]Clonidine binding was markedly decreased by siRNA targeting S1P(1)- and S1P(3)-receptors but not by siRNA against S1P(2)-receptors. Finally, in HEK293 cells transiently expressing human S1P(3)-receptors, sphingosine-1-phosphate, clonidine and moxonidine induced increases in intracellular calcium concentration, moxonidine being more potent than clonidine; this is in agreement with the known properties of the "I(1)-imidazoline receptors". The present results indicate that the "I(1)-imidazoline receptors" mediating effects of clonidine and moxonidine in PC12 and the transfected HEK293 cells belong to the S1P-receptor family; in particular, the data obtained in PC12 cells suggest that the I(1) imidazoline receptors represent a mixture of S1P(1)- and S1P(3)-receptors and/or hetero-dimers of both.
authors.affiliation: University of Bonn, Institute of Pharmacology and Toxicology, Reuterstr. 2b, D-53113 Bonn, Germany. molderings@uni-bonn.de
authors.forename: Gerhard J
authors.initials: GJ
authors.lastname: Molderings
authors.forename: Heinz
authors.initials: H
authors.lastname: Bönisch
authors.forename: Michael
authors.initials: M
authors.lastname: Brüss
authors.forename: Christiana
authors.initials: C
authors.lastname: Wolf
authors.forename: Ivar
authors.initials: I
authors.lastname: von Kügelgen
authors.forename: Manfred
authors.initials: M
authors.lastname: Göthert
mesh_terms: D000818:Animals; D000959:Antihypertensive Agents / Q000378:metabolism; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics; D003000:Clonidine / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics; D006801:Humans; D007022:Hypotension / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism; D007093:Imidazoles / Q000378:metabolism; D054755:Imidazoline Receptors / Q000819:agonists* / Q000378:metabolism*; D008024:Ligands; D008246:Lysophospholipids / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D016716:PC12 Cells; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D011869:Radioligand Assay; D051381:Rats; D011940:Receptor Aggregation / Q000187:drug effects / Q000235:genetics; D049349:Receptors, Lysosphingolipid / Q000187:drug effects* / Q000235:genetics*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism; D014162:Transfection
chemical_list: D000959:Antihypertensive Agents; D007093:Imidazoles; D054755:Imidazoline Receptors; D008024:Ligands; D008246:Lysophospholipids; D020033:Protein Isoforms; D049349:Receptors, Lysosphingolipid; C410887:imidazoline I1 receptors; C060506:sphingosine 1-phosphate; C043482:moxonidine; D003000:Clonidine; D013110:Sphingosine; C032881:lysophosphatidic acid