Voltage-independent activation and deactivation kinetics of Kir4.1/Kir5.1 channels. ( A and C) Inside-out Kir4.1/Kir5.1 current traces elicited with the voltage-step protocols (see insets), which are described in the text and designed for activation (A) or deactivation (C) of currents. (B and D) Time constants of the activation (τ act; B) and deactivation (τ deact; D) of Kir4.1/Kir5.1 currents as a function of the test pulse potential. Time constants in black and red were obtained with single and double exponential functions, respectively. The dashed line denotes the zero-current level. Data are presented as mean ± SEM. n = 8 for activation and n = 6 for deactivation.