Figure 8.

Absence of cooperative interactions between subunits during DA but not 5-HT transport. A, B, COS-7 cells transiently transfected with variable ratios of MTS-insensitive hSERT Y95F/C109A and MTS-sensitive hSERT Y95F/C109A/I172C were treated with 0.25 mm MTSEA for 10 min, washed, and assayed for uptake of either 150 nm [³H]5-HT (A) or 300 nm [³H]DA (B) for 10 min. C, D, COS-7 cells transiently transfected with variable ratios of hSERT Y95F and transport-inactive hSERT Y95F/D98G were assayed for uptake of either 150 nm [³H]5-HT (C) or 300 nm [³H]DA (D) for 10 min. All steps were performed at room temperature. Shown is the average and SEM of six independent experiments, each performed in triplicate. Values from each experiment were normalized to the activity of MTSEA-treated 100% hSERT Y95F/C109A (A, B) or 100% Y95F (C, D). The dotted line shows the activity expected if the activity of a multimer is proportional to the fraction of noninactivated protomers.