Carrier-mediated serotonin release induced by d-fenfluramine: Studies with human neuroblastoma cells transfected with a rat serotonin transporter

The NMB human neuronal cell line, transfected with a newly prepared plasmid expressing rat serotonin transporter (NMB-rSERT), shows specific [H-3]5-HT uptake which is blocked by citalopram and fenfluramine (F) stereoisomers with IC50 values (1 nM, 0.5 mu M (dF) and 5 mu M (1F), respectively) which are similar to those found in rat brain synaptosomes. d-Fenfluramine (0.5 and 10 mu M) also stimulates tritium release from NMB-rSERT cells preloaded with [H-3-]- 5-HT. The d-fenfluramine-induced [H-3-]5-HT release is blocked by 0.3 mu M citalopram and is dependent on the density of SERT expressed per cell, but is not affected by removal of Ca++ ions from the incubation medium. Manipulation of the Nat gradient across the plasma membrane (replacing 60 mM NaCl with an equimolar concentration of KCl or choline) also induced [H-3-]5-HT release from NMB-rSERT cells, which was inhibited by 0.3 mu M citalopram. These results, together with the finding that NMB-rSERT cells preloaded with 500 nM unlabelled 5-HT take up [H-3-]d-fenfluramine, make NMB-rSERT cells a valuable tool for studying the transporter-mediated exchange release induced by amphetamine derivatives. (C) 1997 Published by Elsevier Science Ltd.