Exogenous PIP₂ largely reduces the inward rectification of Kir4.1/Kir5.1 channels. (A and B) Representative Kir4.1/Kir5.1 current traces elicited by the voltage protocol shown at the bottom of A, in control conditions (A) and in the presence of 10 µM PIP₂ (B). (C) Normalized I-V relationships for currents measured at the end of the test pulses, before and after PIP₂ perfusion (n = 7). Currents were normalized to that obtained at −140 mV. For comparison, an ohmic behavior is depicted by a dashed line. (D) Superimposed Kir4.1/Kir5.1 current recordings in the presence of 10 µM PIP₂ and after adding 10 µM SPM (similar results were obtained in four more cells). Currents were elicited to −140 mV for 2 s previous to a depolarizing pulse (2 s) to +100 mV (holding potential = 0 mV). The horizontal dashed lines denote the zero-current level.