Heteromeric Kir4.1/Kir5.1 but not homomeric Kir4.1 channels inwardly rectify in inside-out configuration. (A–E) Representative macroscopic Kir4.1/Kir5.1 (A, C, and D) and Kir4.1 (E) currents recorded in the inside-out configuration when applying the triple-pulse voltage protocol depicted in the inset. The bath (intracellular) solution contained 5 mM (A and E), 1 mM (C), or 10 mM (D) EDTA. (B and F) Normalized I-V relationships for Kir4.1/Kir5.1 (B) and Kir4.1 (F) currents measured at the end of the test pulses and normalized to the amplitude of the current recorded at −140 mV. The dashed line denotes the zero-current level. n = 6–8 cells for each channel and EDTA condition.