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VOLTAGE AND IONIC REGULATION OF HUMAN SEROTONIN TRANSPORTER IN XENOPUS OOCYTES
Author(s) -
Li Cizhen,
Zhong Hua,
Wang Yiyin,
Wang Hongwei,
Yang Zhifang,
Zheng Yanqian,
Liu Kai,
Liu Yuanmou
Publication year - 2006
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.2006.04491.x
Subject(s) - xenopus , extracellular , egta , serotonin , endocrinology , chemistry , voltage clamp , sodium , serotonergic , medicine , synaptic cleft , calcium , neurotransmission , pharmacology , biophysics , biochemistry , membrane potential , biology , receptor , organic chemistry , gene
SUMMARY1 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, CaCl 2 (50 µmol/L) and inositol triphosphate (IP 3 ; 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 < 0.05, n = 7 each). Injection of IP 3 or CaCl 2 increased the hSERT currents by approximately 65% ( P < 0.05; n = 10 each) and the effect of IP 3 was abolished by preinjection of EGTA. 4 These results demonstrate that hSERT activity is not only voltage dependent, but is also affected by intracellular calcium and extracellular sodium and chloride.