Blocking of inactivated hERG channels by hydroxyzine in Xenopus oocytes. (A) Inhibition of inactivated channels by 5 μmol/L hydroxyzine. hERG channels were inactivated by an initial voltage-step to +80 mV, followed by channel opening at 0 mV. (B) The corresponding relative block during the 0 mV step is shown. Maximum inhibition was achieved in the inactivated state during the first step, and no additional time-dependent inhibition occurred upon channel opening during the second voltage step.