Modifications of E290C by negatively charged MTS reagents increased the current. (A and B) MTSES and MTSPeS modifications of WT hK_v7.1 (left) and E290C (right) with 4 mM K⁺_e. MTSES and MTSPeS modifications increased the E290C current but had no appreciable effects on the WT current. (C and D) The current density–voltage relationships of WT and E290C before and after MTSES (C, n = 11) and MTSPeS (D, n = 12) modifications. The outward current density was significantly increased by MTSES and MTSPeS modifications in E290C (*, P < 0.05). The averaged current density from the last 50 ms of the test pulse was used.