3 μCi/mmol) and [3H]DA ([3H]dihydroxyphenylethylamine, [3H]dopamine; 46 μCi/mmol) were purchased from PerkinElmer, Boston, MA. [3H]1-Methyl-4-phenylpyridinium

([3H]MPP+; 85 μCi/mmol) was supplied by American Radiolabeled Libraries Chemicals (St. Louis, MO). FRAX597 chemical structure Paroxetine was from Santa Cruz Biotechnology, mazindole, serotonin, levamisole, cocaine, aminorex, nisoxetine, D-amphetamine, and monensin were purchased from Sigma–Aldrich Co. The samples used in this study were obtained from drug users participating voluntarily and anonymously in the ‘checkit!’ drug prevention program. Three to ten milligrams of substance were scraped into a tapered 2 ml test vial and weighed with an analytical balance. The substance was dissolved in 1 mL of methanol and vortex mixed for 1 min. The solution was centrifuged for 3 min at 10,000g in an Eppendorf centrifuge. Ten microliters of the supernatant were diluted with 0.4 mL of internal standard solution (trazodone 50 μg/mL dissolved in 10 mM aqueous ammonium formate buffer), 2 μl of the solution was analysed

with reversed phase HPLC and LC/mass spectrometry coupling as described in a previous study ( Rosenauer et Capmatinib concentration al. 2013). The generation of HEK293 cell lines expressing the human isoforms of SERT, NET, or DAT (HEK-SERT, HEK-DAT, or HEK-NET, respectively) was described earlier (Scholze et al., 2002). HEK293 cells stably expressing either neurotransmitter transporter were seeded onto poly-d-lysine-coated 96-well

plates (40,000 cells/well), 24 h prior to the experiment. For inhibition experiments, the specific activity of the tritiated substrate was kept constant: [3H]DA, 0.1 μM; [3H]MPP+, 0.015 μM; [3H]5-HT, 0.1 μM. Assay conditions were used as outlined earlier ( Sucic et al., 2010). In brief, the cells were washed twice with Krebs–Ringer–HEPES buffer (KHB; composition: 25 mM HEPES·NaOH, pH 7.4, 120 mM NaCl, 5 mM KCl, 1.2 mM CaCl2, and 1.2 mM the MgSO4 supplemented with 5 mM d-glucose). Then, the diluted reference and sample compounds were added and incubated for 5 min to allow for equilibration with the transporters. Subsequently, the tritiated substrates were added and the reaction was stopped after 1 min (SERT and DAT) and 3 min (NET), respectively. Cells were lysed with 1% SDS and the released radioactivity was quantified by liquid scintillation counting. All determinations were performed in duplicate or triplicate. For release studies, HEK-SERT, HEK-NET, or HEK-DAT cells were grown overnight on round glass coverslips (5-mm diameter, 40,000 cells per coverslip) placed in a 96-well plate and preloaded with 0.4 μM [3H]dopamine, 0.1 μM [3H]MPP+, or 0.4 μM [3H]5-HT for 20 min at 37 °C in a final volume of 0.1 mL/well. Coverslips were then transferred to small superfusion chambers (0.2 ml) and superfused with KHB (25 °C, 0.7 ml × min−1) as described (Scholze et al., 2002).