Figure 2.

Characterization of IRKC. A, Extracellular application of Cs⁺ blocked IRKC in a concentration-dependent manner. B, The concentration–response curve for Cs⁺ blockade of IRKC (IC₅₀ of 0.12 mm; n = 4 for each data point). C, The IRK channels selectively conduct K⁺ ions. When K⁺ was replaced with Na⁺ in the bath, no Cs⁺-sensitive IRKC was observed. D, The ionic selectivity of IRKC was examined by testing the reversal potential (V_r). The V_r was –50 mV when the concentration of extra cellular K⁺ was 20 mm (n = 7). V_r changed to –75 and –100 mV when the concentration of K⁺ in the bath was shifted to 7 mm (n = 4) and 2.6 mm (n = 4), respectively. E, The V_r could be theoretically predicted with the Nernst equation. The observed V_r was consistent with the predicted value, indicating the high K⁺ selectivity of IRK channels. The slope of the line is 1.