Elsevier

European Journal of Pharmacology

Volume 737, 15 August 2014, Pages 202-209
European Journal of Pharmacology

Molecular and cellular pharmacology
Inhibition of HERG potassium channels by domiphen bromide and didecyl dimethylammonium bromide

https://doi.org/10.1016/j.ejphar.2014.05.002Get rights and content

Abstract

Domiphen bromide and didecyl dimethylammonium bromide were widely used environmental chemicals with potent activity on blockade of human ether-a-go-go related gene (HERG) channels. But the mechanism of their action is not clear. The kinetics of block of HERG channels by domiphen bromide and didecyl dimethylammonium bromide was studied in order to characterize the inhibition of HERG currents by these quaternary ammonium compounds (QACs). Domiphen bromide and didecyl dimethylammonium bromide inhibited HERG channel currents in a dose-dependent manner with IC50 values of 9 nM and 5 nM, respectively. Block of HERG channel by domiphen bromide and didecyl dimethylammonium bromide was voltage-dependent and use-dependent. Domiphen bromide and didecyl dimethylammonium bromide caused substantial negative shift of the activation curves, accelerated activated process, but had no effects on the deactivation and reactivation processes. The docking models implied that these two compounds bound to PAS domain of HERG channels and inhibited its function. Our data demonstrated that domiphen bromide and didecyl dimethylammonium bromide blocked the HERG channel with a preference for the activated channel state.

Introduction

Domiphen bromide (DB) and didecyl dimethylammonium bromide (DDB), two members of quaternary ammonium compounds (QACs), are widely used in clinical and industrial fields. Domiphen bromide is used in the treatment of acute infectious oral diseases (Scaglione et al., 1983). Didecyl dimethylammonium bromide is being used in various industrial fields including bio-chemical industries (Kuo and Yu, 2011a, Kuo and Yu, 2011b). The chloride form of DDB is authorized for use in food industries (Mechin et al., 1999). These two compounds, similar to the well-known voltage-gated potassium channel blocker tetraethylammonium (TEA), have four ethyl groups attached to a central nitrogen atom. Previous electrophysiological studies demonstrated that QA׳s binding site was located inside the channel pore, and it accessed this binding site through open potassium channel pore (Armstrong, 1969, Armstrong, 1971). Moreover, findings have been verified that TEA could be trapped inside the channel pore by closure of the activation gate. On the other hand, large QA compounds were reported to block K+ channels by a foot in the door mechanism (Armstrong, 1969, Armstrong, 1971). These two mechanisms may reflect that different compounds cause various alterations on HERG channels kinetics.

The human ether-a-go-go related gene (HERG) potassium channel, a member of voltage-gated potassium channels, plays a pivotal role in cardiac rhythm regulation, especially in the repolarization of the cardiac action potential. Drugs selectively inhibiting HERG channels may reduce the repolarizing cardiac potassium currents, causing the prolonged cardiac action potential and producing long QT syndromes. Thus, the HERG channel has been subjected to a routine test for compound cardiac toxicity in the drug development process. Recently, several QACs including benzethonium chloride, domiphen bromide, and tetra-n-octylammonium bromide have been found to block the HERG channel (Long et al., 2013, Xia et al., 2011). To further investigate the potential mechanisms for the efficacy of HERG inhibition of domiphen bromide and didecyl dimethylammonium bromide, two QACs, we performed detailed studies to explore the effects of domiphen bromide and didecyl dimethylammonium bromide on the use-dependence, voltage-dependence and state-dependence of HERG channels expressed in Chinese hamster ovary (CHO) cells.

Section snippets

Materials

The two quaternary ammonium compounds domiphen bromide and didecyl dimethylammonium bromide as well as other chemicals were purchased from Sigma (St. Louis, MO, USA).

Cell culture

HERG K+ channels stably transfected CHO cell line was purchased from ChanTest (Cleveland, OH, USA). The cells were cultured in 35 mm plastic dishes with culture medium of HAMS F-12 (Invitrogen, Carlsbad, CA, USA), supplemented with 1 mM L-glutamine and 10% fetal bovine serum (Hyclone, Logan, UT, USA) in a humidified, 5% CO2 incubator

Concentration-dependent effects on HERG tail currents

The voltage clamp protocol and the representative traces are shown in Fig. 1; fitting of the data with the Hill equation indicated that the calculated half-maximal inhibitory concentration (IC50) value for domiphen bromide block of peak tail IHERG was 9 nM with a Hill coefficient of 0.24 (Fig. 1A and C). The calculated IC50 value for didecyl dimethylammonium bromide block of peak tail IHERG was 5 nM with a Hill coefficient of 0.45 (Fig. 1B and C). In addition, the inhibitory effects of these two

Discussion

Quaternary ammonium compounds were a large family including numerous widely used environmental chemicals such as tetraethylammonium (TEA), tetra-n-octylammonium bromide, domiphen bromide, benzethonium chloride, etc. Tetra-n-octylammonium bromide and benzethonium chloride have been demonstrated to be highly effective blockers of HERG channels; these two compounds were reported as open HERG channel blockers (Long et al., 2013, Xia et al., 2011). In this study, we compared the kinetics of block of

Acknowledgments

This research was supported by Grants from the National Natural Science Foundation of China (81171037) and 973 Programme(2012CB966404).

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