Figure 3. The channels mediating the E-4031-sensitive current are selective for K⁺ over Na⁺.

Measurement of the reversal potential of the E-4031-sensitive current in 40 mM (A) and 150 mM (B) K⁺ external solution. The pulse protocol consisted of a 10 ms pulse to -120 mV followed by a 70 ms voltage ramp to 40 mV. Holding potential, -20 mV. The E-4031-sensitive current was obtained from the difference between the membrane currents recorded before and after application of 10 μM E-4031. C, reversal potentials measured in 16, 40 and 150 mM K⁺ external solution were corrected for the liquid junction potential and plotted versus external K⁺ concentration (means ±s.d., 3-4 experiments for each concentration). The straight line was calculated from the Nernst equation with a steepness of 58 mV for a 10-fold change in the external K⁺ concentration.