Effect of exogenous SPM on inside-out Kir4.1/Kir5.1 and Kir4.1 currents. (A) Kir4.1/Kir5.1 currents before (control) and after perfusing 1 µM SPM in the bath. Currents were recorded in the inside-out configuration applying the same triple-pulse voltage protocol as for Fig. 2. (B) Normalized I-V relationships for Kir4.1/Kir5.1 in the absence (control) and presence of 1 µM SPM. Currents were measured at the end of the test pulses and normalized to the amplitude of the current recorded at −140 mV in control conditions. (C) Superimposed Kir4.1/Kir5.1 current traces from A illustrating control currents (black traces) and their respective SPM-induced block (red traces) at +40, +60, +80, and +100 mV. (D) Time constants (τ_slow [τ_s] and τ_fast [τ_f]) of Kir4.1/Kir5.1 currents as shown in C, in control conditions and in the presence of 1 µM SPM. (E and F) Current recordings (E) and normalized I-V relationships (F) for Kir4.1 in control and after 1 µM SPM, obtained as described for A and B, respectively. The dashed line denotes the zero-current level. Data are presented as mean ± SEM. n = 5 for Kir4.1/Kir5.1 and n = 11 for Kir4.1. *, P = 0.047; +, P = 0.032; x, P = 0.029.