Electrophysiological Characterization Of A Small Molecular Activator On Human Ether-a-go-go-related Gene(hERG) Potassium Channel

Arrhythmia is a heart disease with high morbidity and mortality.Long QT syndrome(LQTS)is an arrhythmia which caused by obstruction to the smooth permeation of K+ ions through the h ERG channel.The inhibition of h ERG channel function either by gene mutation or pharmacological factors could lead to prolongation of the repolarization process and the QT interval.Excessive prolongation of the action potential at low heart rates could eventually lead to fibrillation and tachycardia of the ventricles in the heart and even sudden death.Pharmacological treatments are far from optimal for LQ TS,and meanwhile drug-induced LQTS through inhibition of h ERG is a major impediment in delivering safe drugs to the market.Until now,many drugs which were withdrawed from the market or given strict limitation for use due to their cardiotoxicities.Not only does it cause huge economic losses to pharmaceutical companies but enormous waste of resources for society.Human ether-a-go-go-related gene(h ERG)encodes the K+ channel that carries the rapid component of the delayed rectifier current in the human heart and plays a significant role in action potential repolarization.Reduced potassium ion outflow and delayed myocardial repolarization are associated with inhibition of h ERG channel function elicited by gene mutations or pharmacological agents on h ERG channel.The inhibition of h ERG channel could produce QT prolongation and increase risk for torsades des pointes(Td P)-triggered sudden cardiac death.Studies on animal experiments indicated that h ERG activators could accelerate the myocardial repolarization through increasing K+ outflow.It suggests that pharmacologicaly targeting and activating h ERG could be an improvement on present strategies.In this study,using patch-clamp electrophysiology,we described two new potent a nd efficacious h ERG channel activator named HW-0168(N-(2-(tert-butyl)phenyl)-6-(4-chlorophenyl)-4-(trifluoromethyl)nicotinamide)and HW-011(N-(4-benzylphenyl)-3-nitrobenzamide).Objective: To elucidate the antiarrhythmic effects of the novel small molecule compounds HW-0168 and HW-011 activating the h ERG potassium channel.Methods: The whole cell patch clamp experiment was used to evaluate the electrophysiological properties of HW-0168 and HW-011 on h ERG potassium channels,and the effects of chemical substances on rat cardiac electrical signals were observed by an experimental method using multi-channel cardiac electrophysiological mapping.Results: 1.The h ERG channel current has a unique dynamics characteristic characterized by rapid voltage-dependent inactivation and slow deactivation.1?M HW-0168 can increase the magnitude of h ERG current in voltage-dependent.2.we confirmed that HW-0168 generated a hyperpolarizing shift in the voltage-de pendence of channel activation and depolarizing shift in the voltage-dependence of channel inactivation.It suggested that the drug might influence the extent of channel activation and inactivation.3.The primary mechanism of HW-0168 to enhance h ERG channel activity is by dramatically slowed current inactivation.4.HW-0168 had no effect on h ERG channel deactivation.5.HW-0168 shortened the action potential duration(APD)of guinea pig myocytes.6.HW-011(1 ?M)enhanced the magnitude of h ERG current in a voltage-dependent manner.7.HW-0168 enhanced the magnitude of h ERG current in a voltage-dependent manner.When the concentration lower than 2 ?M,the enhanced effect with dose-responsed.when the concentration greater than 2 ?M,the enhanced effect will be diminished even to be inhibited.8.The selectivity of the compound to other important ion channels of the heart was evaluated.Nav1.5 inhibited by HW-011(1 ?M)approximately 20% and Cav1.2 inhibited by HW-011(1 ?M)approximately 25%.9.Multi-channel cardiac electrophysiological mapping yield similar results compared to traditional ECG recording methods.This method is reliable and can be used to determine cardiac function parameters of two compounds.Conclusions: The primary mechanism of HW-0168 to enhance h ERG channel activity is by dramatically slowed current inactivation enhanced the magnitude of h ERG current.HW-011 enhanced the magnitude of h ERG current in a voltage-dependent manner.In conclusion,we identified two novel h ERG channel activator that might be a useful tool to further understand the mechanism of h ERG channel and even the long-QT syndrome.