The E290C mutant channel yielded measurable current with less sensitivity to K⁺_e compared with WT hK_v7.1. (A) Current density–voltage relationships of the whole-cell currents from WT hK_v7.1 and E290C mutant channel (n = 13). The averaged current density from the last 50 ms of the test pulse was used. The outward current density of E290C was significantly smaller than that of WT channels (*, P < 0.05). Representative current traces of E290C are shown in the inset on the right. (B) Steady-state voltage-dependent activation of WT and E290C channels. The tail currents immediately after stepping to −30 mV were normalized to the largest tail current and plotted against the preceding prepulse voltages. The midpoint of activation (V_1/2 in mV) and the slope factors (k) of the activation curves obtained from WT and E290C channels are −20.4 ± 1.9 and 9.2 ± 1.1 for WT hK_v7.1 (n = 11) and −13.3 ± 0.8 and 11 ± 1.2 for E290C (n = 9), respectively. (C) Representative current traces (left) of E290C with varied K⁺_e. The ratios of the steady state to the peak current density at 40 mV are shown on the right. The ratios are significantly larger than that of WT channels (*, P < 0.05). (D) The relationship between the relative magnitude of the E290C current and K⁺_e. The experimental data (○, n = 7) were approaching the predicted current magnitude (■) by the GHK equation. This is in contrast to the WT hK_v7.1 channels (□), which were at odds with predicted values by the GHK equation.