Modifications of E284C, D286C, and E295C by charged MTS reagents did not alter the current. (A and B) MTSES and MTSEA modifications of the three mutant channels. (C and D) The current density–voltage relationships of the three mutant channels before and after MTSES (C, n = 6, 5, and 5 for E284C, D286C, and E295C, respectively) and MTSEA (D, n = 5 for each mutant) modifications. The outward current density was not significantly altered by MTSES and MTSEA modification for all three mutants. The averaged current density from the last 50 ms of the test pulse was used.