Ionic and ligand effects on activation. HeLa cells expressing the Q111C mutant (A and C) or the N112C mutant (B and D) were treated with MTSEA or MTSET, respectively, at the indicated concentrations for 10 min in the presence of NaCl (control), NMDG-Cl or Na-isethionate, or in the presence of 2 μM 5-HTor cocaine (C and D), and then washed and assayed for 5-HT influx. The figure shows results of a typical experiment that was replicated at least six times with similar results.