title: Unifying concept of serotonin transporter-associated currents.
abstract: Serotonin (5-HT) uptake by the human serotonin transporter (hSERT) is driven by ion gradients. The stoichiometry of transported 5-HT and ions is predicted to result in electroneutral charge movement. However, hSERT mediates a current when challenged with 5-HT. This discrepancy can be accounted for by an uncoupled ion flux. Here, we investigated the mechanistic basis of the uncoupled currents and its relation to the conformational cycle of hSERT. Our observations support the conclusion that the conducting state underlying the uncoupled ion flux is in equilibrium with an inward facing state of the transporter with K+ bound. We identified conditions associated with accumulation of the transporter in inward facing conformations. Manipulations that increased the abundance of inward facing states resulted in enhanced steady-state currents. We present a comprehensive kinetic model of the transport cycle, which recapitulates salient features of the recorded currents. This study provides a framework for exploring transporter-associated currents.
authors.affiliation: Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria.
authors.forename: Klaus
authors.initials: K
authors.lastname: Schicker
authors.affiliation: Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria.
authors.forename: Zeljko
authors.initials: Z
authors.lastname: Uzelac
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066.
authors.forename: Joan
authors.initials: J
authors.lastname: Gesmonde
authors.affiliation: Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria.
authors.forename: Simon
authors.initials: S
authors.lastname: Bulling
authors.affiliation: Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stockner
authors.affiliation: Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Freissmuth
authors.affiliation: Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Boehm
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066.
authors.forename: Gary
authors.initials: G
authors.lastname: Rudnick
authors.affiliation: Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria.
authors.forename: Harald H
authors.initials: HH
authors.lastname: Sitte
authors.affiliation: Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria. Electronic address: walter.sandtner@meduniwien.ac.at.
authors.forename: Walter
authors.initials: W
authors.lastname: Sandtner
mesh_terms: D000818:Animals; D004553:Electric Conductivity; D055724:Electrophysiological Phenomena / Q000187:drug effects; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism; D011487:Protein Conformation / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology; D050486:Serotonin Plasma Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D050486:Serotonin Plasma Membrane Transport Proteins; D012701:Serotonin; D011188:Potassium
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