Characterization of an allosteric citalopram-binding site at the serotonin transporter

J Neurochem. 2005 Jan;92(1):21-8. doi: 10.1111/j.1471-4159.2004.02835.x.

Abstract

The serotonin transporter (SERT), which belongs to a family of sodium/chloride-dependent transporters, is the major pharmacological target in the treatment of several clinical disorders, including depression and anxiety. In the present study we show that the dissociation rate, of [3H]S-citalopram from human SERT, is retarded by the presence of serotonin, as well as by several antidepressants, when present in the dissociation buffer. Dissociation of [3H]S-citalopram from SERT is most potently inhibited by S-citalopram followed by R-citalopram, sertraline, serotonin and paroxetine. EC50 values for S- and R-citalopram are 3.6 +/- 0.4 microm and 19.4 +/- 2.3 microm, respectively. Fluoxetine, venlafaxine and duloxetine have no significant effect on the dissociation of [3H]S-citalopram. Allosteric modulation of dissociation is independent of temperature, or the presence of Na+ in the dissociation buffer. Dissociation of [3H]S-citalopram from a complex with the SERT double-mutant, N208Q/N217Q, which has been suggested to be unable to self-assemble into oligomeric complexes, is retarded to an extent similar to that found with the wild-type, raising the possibility that the allosteric mechanism is mediated within a single subunit. A species-scanning mutagenesis study comparing human and bovine SERT revealed that Met180, Tyr495 and Ser513 are important residues in mediating the allosteric effect, as well as contributing to high-affinity binding at the primary site.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allosteric Site / physiology*
  • Animals
  • Cattle
  • Cell Line
  • Citalopram / metabolism*
  • Dose-Response Relationship, Drug
  • Humans
  • Membrane Glycoproteins / metabolism*
  • Membrane Transport Proteins / metabolism*
  • Nerve Tissue Proteins / metabolism*
  • Serotonin / metabolism*
  • Serotonin Agents / metabolism
  • Serotonin Plasma Membrane Transport Proteins

Substances

  • Membrane Glycoproteins
  • Membrane Transport Proteins
  • Nerve Tissue Proteins
  • SLC6A4 protein, human
  • Serotonin Agents
  • Serotonin Plasma Membrane Transport Proteins
  • Citalopram
  • Serotonin