Sensitivity of SERT mutants to MTSEA. HeLa cells expressing either pRSTag (SERT wild type), C109A, I172C, Res-FLAG, or Sens-myc were incubated with 0.25 mM MTSEA for 10 min and then were assayed for transport activity. Filled bars, control; open bars, MTSEA; gray bars, cocaine control for nonspecific activity.