Fig. 3. Concentration-dependence and reversibility of the blocking action of verapamil on hKv1.5 current. (A) Superimposed hKv1.5 currents during depolarizing voltage-steps to +30 mV in the absence and presence of increasing concentrations of verapamil from 0.1 to 10 mM applied in a cumulative manner. (B) The percent inhibition of hKv1.5 current measured at the end of test potential ((1 - I_Verapamil/I_Control) ´ 100) was plotted as a function of verapamil concentrations. The smooth curve through the data points represents a least-squares fit of Hill equation. (C) Time course of the changes in the late current amplitude of hKv1.5 current by exposure to 10 mM verapamil. Inset, superimposed hKv1.5 currents recorded at time points a, b and c.