Figure 3. Drug sensitivity of Kv1.5 Na⁺ currents and envelope of tails test.

A, effect of 50 μM 4-AP, showing reversibility of action. B, lack of effect of 0.5 mM DIDS on Na⁺ currents. In both A and B cells were held at -80 mV and pulsed to +60 mV at 0.1 Hz. Pipette and bath solutions contained 130 mM ${\text{N }}_{\text{i}}^{+}$/5 mM ${\text{N }}_{\text{o}}^{+}$. C, mean data for actions of 1 mM 4-AP and 0.5 mM DIDS vs. control, n = 4–6. 4-AP data are significantly different from controls (*P < 0.001). D, superimposed currents during depolarization, and subsequent tail currents. Solutions contained symmetrical 135 mM ${\text{N }}_{\text{i}}^{+}$/${\text{N }}_{\text{o}}^{+}$. Pulse protocol (top): initial 10 ms depolarization from -80 to +80 mV incremented by 100 ms for each subsequent pulse. E, as for D with initial pulse duration of 10 ms, with 10 ms increment. Note that the amplitude of the fast tail current on repolarization (I_tail) was scaled to the preceding outward current amplitude at the end of the pulse (I_step). Dotted lines denote zero current level. F, the I_tail/I_step ratio as a function of pulse duration. Data represent means ±s.e.m. (n = 9).