Fig. 8.

Kinetic analysis of [³H]5-HT uptake. Initial rates of [³H]5-HT uptake in presence of increasing extravesicular concentrations of total 5-HT over range of 150–800 nM were determined. Brush-border membrane vesicles were preloaded with 300 mM mannitol, 10 mM Tris-HEPES, pH 7.4, and 0.1 mM MgSO₄. Uptake was measured at 10 s by diluting vesicles in medium containing 100 mM NaCl or K-gluconate; 100 mM mannitol; 10 mM Tris-HEPES, pH 7.4; 0.1 mM MgSO₄; [³H]5-HT; and varying concentrations of unlabeled 5-HT. Results are means ± SE of NaCl-sensitive component of total 5-HT uptake and are representative of 3 separate membrane preparations.