title: Early fluorescence signals detect transitions at mammalian serotonin transporters.
abstract: The mammalian serotonin transporters rSERT or hSERT were expressed in oocytes and labeled with sulforhodamine-MTS. The endogenous Cys-109 residue contributes most of the signal, and the labeled transporter shows normal function. The SERT fluorescence decreases in the presence of 5-HT and also depends on the inorganic substrates of SERT. The fluorescence also increases with membrane depolarization. During voltage-jump experiments, fluorescence relaxations show little inactivation or history dependence. The fluorescence signal has a voltage dependence similar to that of the prepriming step of the previously described voltage-dependent transient current. However, the fluorescence relaxations are the fastest voltage-dependent events yet studied at SERT; their time constants of approximately 8-30 ms are severalfold faster than the prepriming or inactivation phases of the transient currents. These fluorescence signals are interpreted within the framework of the gate-lumen-gate model. The signals may monitor initial events at the outer gate.
authors.affiliation: Division of Biology 156-29, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Henry A
authors.initials: HA
authors.lastname: Lester
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D004594:Electrophysiology; D005456:Fluorescent Dyes / Q000494:pharmacology; D050485:GABA Plasma Membrane Transport Proteins; D006801:Humans; D007477:Ions; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D026901:Membrane Transport Proteins; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009419:Nerve Tissue Proteins; D009865:Oocytes / Q000378:metabolism; D027361:Organic Anion Transporters; D051381:Rats; D012235:Rhodamines / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D050486:Serotonin Plasma Membrane Transport Proteins; D013997:Time Factors; D014981:Xenopus
chemical_list: D002352:Carrier Proteins; D005456:Fluorescent Dyes; D050485:GABA Plasma Membrane Transport Proteins; D007477:Ions; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D027361:Organic Anion Transporters; D012235:Rhodamines; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; C493232:Slc6a4 protein, rat; C022027:lissamine rhodamine B; D012701:Serotonin