IK_V decays and blocking effect of isradipine. (A) IK_V records were obtained in response to 500-ms voltage pulses of 60–200-mV amplitude, with 20-mV increments. (B) IK_V from the same fiber as in A, but after exposure to 0.5 µM isradipine. (C) Voltage dependence of peak IK_V (closed circles) and peak gK_V (open circles) determined from the data in A (black circles, control conditions) and B (red circles, isradipine). The black solid lines are double Boltzmann fits to the control data with the following parameters: A = 4.44 mS/cm²; ε = 0.33; V1 = −3.2 mV; K1 = 6.2 mV; V2 = 44.7 mV; K2 = 17.4 mV. The red solid lines are double Boltzmann fits to the isradipine data with the following parameters: A = 2.68 mS/cm²; ε = 0.31; V1 = −1.8 mV; K1 = 7.0 mV; V2 = 36.7 mV; K2 = 14.8 mV. (D) Mean peak gK_V (pooled data) obtained under control conditions (black circles; same data as in Fig. 1 D) and in the presence of isradipine (red circles; n = 6). The red line is a double Boltzmann fit to the isradipine data with the following parameters (mean ± SD): A = 2.90 ± 0.7 mS/cm² (*); ε = 0.28 ± 0.09 (*); V1 = −1.7 ± 2.8 mV (*); K1 =7.6 ± 1.5 mV; V2 =40 ± 6 mV; K2 = 20.7 ± 3.5 mV. The * indicates statistical significance with respect to the control (P < 0.05). Error bars represent SEM.