Inward rectification of Kir4.1 and Kir4.1/Kir5.1 channels in whole-cell control conditions. (A and C) Macroscopic whole-cell Kir4.1/Kir5.1 (A) and Kir4.1 (C) currents in HEK-293 cells. Currents were evoked by using the voltage-step protocol shown in the inset at the center of the four panels. For clarity, currents at potentials −70, −50, −30, and −10 mV are not shown. The inset of A corresponds to the amplification of the first 50 ms of outward currents from this panel. The dashed line denotes the zero-current level. (B and D) Normalized I-V relationships for Kir4.1/Kir5.1 (B) and Kir4.1 (D) currents measured at the end of the test pulses and normalized to the amplitude of the current recorded at −120 mV. n = 9 (Kir4.1/Kir5.1) and n = 6 (Kir4.1).