Inhibition of the HERG channel by droperidol depends on channel gating and involves the S6 residue F656.
BACKGROUND
Droperidol has a central antiemetic action and is widely used in the fields of psychiatry, anesthesia, and emergency medicine. It has been associated with prolongation of the QT interval of the electrocardiogram, and it may also be associated with torsades de pointes and sudden death. Although QT prolongation is consistent with droperidol-induced increases in cardiac ventricular action potential duration, the cellular mechanism for these observations has not been clearly studied. The rapidly activating delayed rectifier potassium channel, IKr, is a primary site of action of drugs causing QT prolongation and is encoded by the human-ether-a-go-go-related gene (HERG). To determine the mechanism underlying these clinical findings, we investigated the effect of droperidol on human HERG potassium channels.


METHODS
Wild type and mutant HERG channels were heterologously expressed in human embryonic kidney 293 cells, and the current was recorded by using whole cell patch clamp technique (22-24 degrees C).


RESULTS
HERG tail currents following test pulses to 50 mV were inhibited by droperidol with an IC(50) of 77.3 +/- 9.6 nM (n = 8). The onset of block was fast and inhibition was completely reversible upon washout. Droperidol affected HERG channels mainly in their open and inactivated states. The effects were use-dependent with a stronger steady-state level of block at higher frequencies. The activation curve was slightly shifted towards more negative potentials (P < 0.05, n = 8) and the time course of inactivation was significantly decreased (P < 0.05, n = 8) by 100 nM droperidol. But there was no relevant effect on HERG channel deactivation. The potency for block of HERG channels by droperidol was significantly decreased with mutation of Phe-656 to Thr or mutation of Ser-631 to Ala, respectively. However, mutation of Phe-656 to Met or the double mutation F656M/S631A had no effect on channel sensitivity to block by droperidol.


CONCLUSIONS
Droperidol potently inhibits transfected HERG channels and this is the probable mechanism for QT prolongation. Channel blockade shows greatest affinity for the open and inactivated state. Aromatic residue at position 656 may participate in droperidol binding, and inactivation gating can induce a conformational state that optimizes droperidol binding to the channel.
Luo
Tao
T
Department of Anesthesiology, Renmin Hospital of Wuhan University, 99 Ziyang Road, Wuhan 430060, China. luotao_wh@yahoo.com
Luo
Ailin
A
Liu
Miu
M
Liu
Xianyi
X
D002460:Cell Line; D004329:Droperidol / Q000494:pharmacology*; D000072237:ERG1 Potassium Channel; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels / Q000037:antagonists & inhibitors* / Q000235:genetics; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007668:Kidney; D007700:Kinetics; D018408:Patch-Clamp Techniques; D014162:Transfection
D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D004329:Droperidol