Figure 6.

5-HT and DA added extracellularly cause efflux of preloaded [³H]5-HT but little or no efflux of preloaded [³H]DA. COS-7 cells transfected with hSERT WT were preloaded with [³H]5-HT (A) or [³H]DA (B) for 45 min at room temperature followed by washes every 5 min for 45 min to give similar concentration of intracellular substrate. Cells were then incubated with PBS alone or with PBS containing 20 μm 5-HT or 2 mm DA. At specified time points, half of the supernatant was collected and prepared for scintillation counting. Released substrate is expressed as the radioactivity in the complete supernatant fraction as a percentage of the radioactivity present in the cells before efflux was initiated. The mean and SEM of six wells are plotted for efflux. Significance levels are indicated for control versus 5-HT or DA by the two-tailed t test (***p < 0.001).