VOLTAGE AND IONIC REGULATION OF HUMAN SEROTONIN TRANSPORTER IN XENOPUS OOCYTES

SUMMARY 1 The serotoninergic system is known to be involved in the control of multiple behavioural and physiological functions. The serotonin (5‐hydroxtryptamine; 5‐HT) transporter (SERT), which controls the synaptic 5‐HT concentration through re‐uptake of this neurotransmitter into presynaptic terminals, has been a primary therapeutic target for various psychiatric and peripheral disorders. The aim of the present study was to identify the regulatory mechanism(s) of the human SERT (hSERT) in heterologously expressed oocytes. 2 The hSERT cRNA was transcribed in vitro and injected into Xenopus oocytes. The 5‐HT‐induced transporter currents were measured by voltage clamp. The effects of extracellular sodium or chloride were studied by replacement perfusion with tetramethylammonium‐chloride (96 mmol/L) or sodium acetate (96 mmol/L). In addition, to alter the internal calcium concentration, CaCl2 (50 µmol/L) and inositol triphosphate (IP3; 50 µmol/L), with or without EGTA (2.5 mmol/L), were injected into oocytes. The specificity of 5‐HT‐sensitive currents was determined by the use of the SERT antagonist desipramine and niflumic acid to block background chloride currents. 3 The hSERT‐expressing oocytes displayed voltage‐dependent, 5‐HT‐induced currents that increased at negative potentials. Replacing extracellular sodium or chloride significantly decreased the hSERT currents by 89 and 45%, respectively (P