Modifications of E290C by positively charged MTS reagents decreased the current. (A and B) MTSEA and MTSET modifications of WT hK_v7.1 (left) and E290C (right) with 4 mM K⁺_e. MTSEA and MTSET modifications decreased the E290C current but had no appreciable effects on the WT current. (C and D) The current density–voltage relationship of WT and E290C before and after MTSEA (C, n = 7) and MTSET (D, n = 9) modifications. The outward current density was significantly reduced by MTSEA and MTSET modifications (*, P < 0.05). The averaged current density from the last 50 ms of the test pulse was used.