Effects of the histamine H(1) receptor antagonist hydroxyzine on hERG K(+) channels and cardiac action potential duration.

AIM: To investigate the effects of hydroxyzine on human ether-a-go-go-related gene (hERG) channels to determine the electrolphysiological basis for its proarrhythmic effects.
METHODS: hERG channels were expressed in Xenopus oocytes and HEK293 cells, and the effects of hydroxyzine on the channels were examined using two-microelectrode voltage-clamp and patch-clamp techniques, respectively. The effects of hydroxyzine on action potential duration were examined in guinea pig ventricular myocytes using current clamp.
RESULTS: Hydroxyzine (0.2 and 2 μmol/L) significantly increased the action potential duration at 90% repolarization (APD(90)) in both concentration- and time-dependent manners. Hydroxyzine (0.03-3 μmol/L) blocked both the steady-state and tail hERG currents. The block was voltage-dependent, and the values of IC(50) for blocking the steady-state and tail currents at +20 mV was 0.18±0.02 μmol/L and 0.16±0.01 μmol/L, respectively, in HEK293 cells. Hydroxyzine (5 μmol/L) affected both the activated and the inactivated states of the channels, but not the closed state. The S6 domain mutation Y652A attenuated the blocking of hERG current by ~6-fold.
CONCLUSION: The results suggest that hydroxyzine could block hERG channels and prolong APD. The tyrosine at position 652 in the channel may be responsible for the proarrhythmic effects of hydroxyzine.