Voltage dependence of hydroxyzine-induced blockade of hERG channels expressed in Xenopus oocytes. (A) Current traces from a cell depolarized to −20 mV (left panel), +10 mV (middle panel), or +40 mV (right panel) before and after application of 5 μmol/L hydroxyzine, showing increased blockade of hERG current at more positive potentials. The protocol consisted of 4 s depolarizing steps to −20 mV, +10 mV, or +40 mV from a holding potential of −70 mV, followed by repolarization to −60 mV. (B) Hydroxyzine-induced hERG current inhibition at various voltages. At each depolarizing voltage step (-20, +10, or +40 mV), the tail currents in the presence of 5 μmol/L hydroxyzine were normalized to the tail current obtained in the absence of drug. n=4.