Heterogeneity of antidepressant binding sites on the recombinant rat serotonin transporter SERT1.
Antidepressant drugs block the uptake of serotonin into serotonergic nerve terminals and blood platelets. Here, binding of the tricyclic antidepressant [3H]imipramine to the recombinant rat serotonin transporter SERT1 expressed in human embryonic kidney cells was found to be nonhomogeneous. Scatchard analysis and competition experiments revealed the existence of two distinct antidepressant binding sites. At site 1, [3H]imipramine binding was strictly sodium-dependent with an apparent KD of approximately 10 nM. In contrast, [3H]imipramine binding to site 2 occurred also in the absence of sodium and exhibited a lower affinity. Binding of the nontricyclic antidepressant [3H]citalopram was observed only at site 2. The natural substrate of this carrier, serotonin, competitively inhibited antidepressant binding at both sites; however, its affinity to site 2 was approximately 5-fold lower. These data provide a molecular explanation for the distinct pharmacological actions of different antidepressants.
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Abteilung Neurochemie, Max-Planck-Institut für Hirnforschung, Frankfurt, Germany.
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D000818:Animals; D000928:Antidepressive Agents / Q000378:metabolism*; D000929:Antidepressive Agents, Tricyclic / Q000378:metabolism; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D015283:Citalopram / Q000378:metabolism*; D006801:Humans; D007099:Imipramine / Q000378:metabolism*; D008024:Ligands; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D011485:Protein Binding; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins; D012964:Sodium / Q000378:metabolism
D000928:Antidepressive Agents; D000929:Antidepressive Agents, Tricyclic; D002352:Carrier Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; C493232:Slc6a4 protein, rat; D015283:Citalopram; D012701:Serotonin; D012964:Sodium; D007099:Imipramine