Figure 4.
Effects of varying concentrations of 4-AP on adult mouse ventricular K+ currents. Outward K+ currents were recorded as described in Fig. 1 during 4.5-s depolarizing voltage steps to −20 to +60 mV from a holding potential of −70 mV; records from three cells exposed to different concentrations (10 μM, 0.5 mM, and 5 mM) of 4-AP are presented. In each example, control currents (A, D, and G) were recorded before application of 4-AP; cells were the exposed to (10 μM, 0.5 mM, or 5 mM) 4-AP, and when the effect (of 4-AP) reached steady state, the currents in the presence of 10 μM (B), 0.5 mM (E), and 5 mM (H) 4-AP were recorded. In B, E, and H, the currents in the presence of 4-AP are plotted as solid lines, and the control records (A, D, and G, respectively) are replotted as points to facilitate comparison. The waveforms of the 10 μM (C), 0.5 mM (F), and 5 mM (I) 4-AP–sensitive currents were obtained by off-line digital subtraction of the currents in the presence of 4-AP from the controls. For each 4-AP concentration, similar results were obtained in experiments on four cells. Scale bars, 2 nA and 500 ms.