Probucol-induced hERG Channel Reduction can be Rescued by Matrine and Oxymatrinein vitro

Background: The human ether-a-go-go-related gene (hERG) potassium channel is the rapidly activating component of cardiac delayed rectifier potassium current (IKr), which is a crucial determinant of cardiac repolarization. The reduction of hERG current is commonly believed to cause Long QT Syndrome (LQTs). Probucol, a cholesterol-lowering drug, induces LQTs by inhibiting the expression of the hERG channel. Unfortunately, there is currently no effective therapeutic method to rescue probucol-induced LQTs. Methods: Patch-clamp recording techniques were used to detect the action potential duration (APD) and current of hERG. Western blot was performed to measure the expression levels of proteins. Results: In this study, we demonstrated that 1 μM matrine and oxymatrine could rescue the hERG current and hERG surface expression inhibited by probucol. In addition, matrine and oxymatrine significantly shortened the prolonged action potential duration induced by probucol in neonatal cardiac myocytes. We proposed a novel mechanism underlying the probucol induced decrease in the expression of transcription factor Specificity protein 1 (Sp1), which is an established transactivator of the hERG gene. We also demonstrated that matrine and oxymatrine were able to upregulate Sp1 expression which may be one of the possible mechanisms by which matrine and oxymatrine rescued probucol-induced hERG channel deficiency. Conclusion: Our current results demonstrate that matrine and oxymatrine could rescue probucol-induced hERG deficiency in vitro, which may lead to potentially effective therapeutic drugs for treating acquired LQT2 by probucol in the future.

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Loss of ATP-Sensitive Potassium Channel Surface Expression in Heart Failure Underlies Dysregulation of Action Potential Duration and Myocardial Vulnerability to Injury

PLoS ONE ◽

10.1371/journal.pone.0151337 ◽

2016 ◽

Vol 11 (3) ◽

pp. e0151337 ◽

Cited By ~ 3

Author(s):

Zhan Gao ◽

Ana Sierra ◽

Zhiyong Zhu ◽

Siva Rama Krishna Koganti ◽

Ekaterina Subbotina ◽

...

Keyword(s):

Heart Failure ◽

Action Potential ◽

Potassium Channel ◽

Action Potential Duration ◽

Surface Expression ◽

Channel Surface

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Lipopolysaccharide prolongs action potential duration in HL-1 mouse cardiomyocytes

AJP Cell Physiology ◽

10.1152/ajpcell.00173.2012 ◽

2012 ◽

Vol 303 (8) ◽

pp. C825-C833 ◽

Cited By ~ 5

Author(s):

Robert Wondergem ◽

Bridget M. Graves ◽

Chuanfu Li ◽

David L. Williams

Keyword(s):

Action Potential ◽

Action Potential Duration ◽

Salmonella Enteritidis ◽

Time Course ◽

Outward Current ◽

Cell Voltage ◽

Delayed Rectifier ◽

Maximal Effect ◽

Cellular Mechanisms ◽

Whole Cell

Sepsis has deleterious effects on cardiac function including reduced contractility. We have shown previously that lipopolysaccharides (LPS) directly affect HL-1 cardiac myocytes by inhibiting Ca2+ regulation and by impairing pacemaker “funny” current, If. We now explore further cellular mechanisms whereby LPS inhibits excitability in HL-1 cells. LPS (1 μg/ml) derived from Salmonella enteritidis decreased rate of firing of spontaneous action potentials in HL-1 cells, and it increased their pacemaker potential durations and decreased their rates of depolarization, all measured by whole cell current clamp. LPS also increased action potential durations and decreased their amplitude in cells paced at 1 Hz with 0.1 nA, and 20 min were necessary for maximal effect. LPS decreased the amplitude of a rapidly inactivating inward current attributed to Na+ and of an outward current attributed to K+; both were measured by whole cell voltage clamp. The K+ currents displayed a resurgent outward tail current, which is characteristic of the rapid delayed-rectifier K+ current, IKr. LPS accordingly reduced outward currents measured with pipette Cs+ substituted for K+ to isolate IKr. E-4031 (1 μM) markedly inhibited IKr in HL-1 cells and also increased action potential duration; however, the direct effects of E-4031 occurred minutes faster than the slow effects of LPS. We conclude that LPS increases action potential duration in HL-1 mouse cardiomyocytes by inhibition of IKr and decreases their rate of firing by inhibition of INa. This protracted time course points toward an intermediary metabolic event, which either decreases available mouse ether-a-go-go (mERG) and Na+ channels or potentiates their inactivation.

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Polarized localization of voltage-gated Na+ channels is regulated by concerted FGF13 and FGF14 action

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1521194113 ◽

2016 ◽

Vol 113 (19) ◽

pp. E2665-E2674 ◽

Cited By ~ 33

Author(s):

Juan Lorenzo Pablo ◽

Chaojian Wang ◽

Matthew M. Presby ◽

Geoffrey S. Pitt

Keyword(s):

Action Potential ◽

Hippocampal Neurons ◽

Single Point ◽

Point Mutations ◽

Surface Expression ◽

Voltage Gated ◽

Voltage Gated Sodium Channels ◽

Action Potential Initiation ◽

Potential Initiation

Clustering of voltage-gated sodium channels (VGSCs) within the neuronal axon initial segment (AIS) is critical for efficient action potential initiation. Although initially inserted into both somatodendritic and axonal membranes, VGSCs are concentrated within the axon through mechanisms that include preferential axonal targeting and selective somatodendritic endocytosis. How the endocytic machinery specifically targets somatic VGSCs is unknown. Here, using knockdown strategies, we show that noncanonical FGF13 binds directly to VGSCs in hippocampal neurons to limit their somatodendritic surface expression, although exerting little effect on VGSCs within the AIS. In contrast, homologous FGF14, which is highly concentrated in the proximal axon, binds directly to VGSCs to promote their axonal localization. Single-point mutations in FGF13 or FGF14 abrogating VGSC interaction in vitro cannot support these specific functions in neurons. Thus, our data show how the concerted actions of FGF13 and FGF14 regulate the polarized localization of VGSCs that supports efficient action potential initiation.

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Pharmacological block of the slow component of the outward delayed rectifier current (I Ks ) fails to lengthen rabbit ventricular muscle QTc and action potential duration

British Journal of Pharmacology ◽

10.1038/sj.bjp.0703777 ◽

2001 ◽

Vol 132 (1) ◽

pp. 101-110 ◽

Cited By ~ 78

Author(s):

Csaba Lengyel ◽

Norbert Iost ◽

László Virág ◽

András Varró ◽

David A Lathrop ◽

...

Keyword(s):

Action Potential ◽

Action Potential Duration ◽

Slow Component ◽

Delayed Rectifier ◽

Ventricular Muscle ◽

Delayed Rectifier Current ◽

Rabbit Ventricular Muscle

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High Glucose Represses hERG K+ Channel Expression through Trafficking Inhibition

Cellular Physiology and Biochemistry ◽

10.1159/000430353 ◽

2015 ◽

Vol 37 (1) ◽

pp. 284-296 ◽

Cited By ~ 10

Author(s):

Yuan-Qi Shi ◽

Meng Yan ◽

Li-Rong Liu ◽

Xiao Zhang ◽

Xue Wang ◽

...

Keyword(s):

Western Blot ◽

High Glucose ◽

Qt Prolongation ◽

Herg Channel ◽

K Channel ◽

Delayed Rectifier ◽

Patch Clamp Technique ◽

Down Regulation ◽

Channel Trafficking ◽

Herg Current

Background/Aims: Abnormal QT prolongation is the most prominent cardiac electrical disturbance in patients with diabetes mellitus (DM). It is well known that the human ether-ago-go-related gene (hERG) controls the rapid delayed rectifier K+ current (IKr) in cardiac cells. The expression of the hERG channel is severely down-regulated in diabetic hearts, and this down-regulation is a critical contributor to the slowing of repolarization and QT prolongation. However, the intracellular mechanisms underlying the diabetes-induced hERG deficiency remain unknown. Methods: The expression of the hERG channel was assessed via western blot analysis, and the hERG current was detected with a patch-clamp technique. Results: The results of our study revealed that the expression of the hERG protein and the hERG current were substantially decreased in high-glucose-treated hERG-HEK cells. Moreover, we demonstrated that the high-glucose-mediated damage to the hERG channel depended on the down-regulation of protein levels but not the alteration of channel kinetics. These discoveries indicated that high glucose likely disrupted hERG channel trafficking. From the western blot and immunoprecipitation analyses, we found that high glucose induced trafficking inhibition through an effect on the expression of Hsp90 and its interaction with hERG. Furthermore, the high-glucose-induced inhibition of hERG channel trafficking could activate the unfolded protein response (UPR) by up-regulating the expression levels of activating transcription factor-6 (ATF-6) and the ER chaperone protein calnexin. In addition, we demonstrated that 100 nM insulin up-regulated the expression of the hERG channel and rescued the hERG channel repression caused by high glucose. Conclusion: The results of our study provide the first evidence of a high-glucose-induced hERG channel deficiency resulting from the inhibition of channel trafficking. Furthermore, insulin promotes the expression of the hERG channel and ameliorates the high-glucose-induced inhibition of the hERG channel.

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Electrophysiological characterization of the hERG R56Q LQTS variant and targeted rescue by the activator RPR260243

The Journal of General Physiology ◽

10.1085/jgp.202112923 ◽

2021 ◽

Vol 153 (10) ◽

Author(s):

Jacob M. Kemp ◽

Dominic G. Whittaker ◽

Ravichandra Venkateshappa ◽

ZhaoKai Pang ◽

Raj Johal ◽

...

Keyword(s):

Action Potential ◽

Refractory Period ◽

Herg Channel ◽

Type I ◽

Early Repolarization ◽

Diastolic Interval ◽

Therapeutic Opportunity ◽

Herg Current ◽

Electrophysiological Characterization ◽

Resurgent Current

Human Ether-à-go-go (hERG) channels contribute to cardiac repolarization, and inherited variants or drug block are associated with long QT syndrome type 2 (LQTS2) and arrhythmia. Therefore, hERG activator compounds present a therapeutic opportunity for targeted treatment of LQTS. However, a limiting concern is over-activation of hERG resurgent current during the action potential and abbreviated repolarization. Activators that slow deactivation gating (type I), such as RPR260243, may enhance repolarizing hERG current during the refractory period, thus ameliorating arrhythmogenicity with reduced early repolarization risk. Here, we show that, at physiological temperature, RPR260243 enhances hERG channel repolarizing currents conducted in the refractory period in response to premature depolarizations. This occurs with little effect on the resurgent hERG current during the action potential. The effects of RPR260243 were particularly evident in LQTS2-associated R56Q mutant channels, whereby RPR260243 restored WT-like repolarizing drive in the early refractory period and diastolic interval, combating attenuated protective currents. In silico kinetic modeling of channel gating predicted little effect of the R56Q mutation on hERG current conducted during the action potential and a reduced repolarizing protection against afterdepolarizations in the refractory period and diastolic interval, particularly at higher pacing rates. These simulations predicted partial rescue from the arrhythmic effects of R56Q by RPR260243 without risk of early repolarization. Our findings demonstrate that the pathogenicity of some hERG variants may result from reduced repolarizing protection during the refractory period and diastolic interval with limited effect on action potential duration, and that the hERG channel activator RPR260243 may provide targeted antiarrhythmic potential in these cases.

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Biophysical Properties and Responses to Neurotransmitters of Petrosal and Geniculate Ganglion Neurons Innervating the Tongue

Journal of Neurophysiology ◽

10.1152/jn.2000.84.3.1404 ◽

2000 ◽

Vol 84 (3) ◽

pp. 1404-1413 ◽

Cited By ~ 28

Author(s):

Tomoshige Koga ◽

Robert M. Bradley

Keyword(s):

Action Potential ◽

Action Potentials ◽

Membrane Properties ◽

Patch Clamp Recording ◽

Potential Decay ◽

Ganglion Neurons ◽

Fast Rise ◽

Posterior Tongue ◽

Passive Membrane Properties

The properties of afferent sensory neurons supplying taste receptors on the tongue were examined in vitro. Neurons in the geniculate (GG) and petrosal ganglia (PG) supplying the tongue were fluorescently labeled, acutely dissociated, and then analyzed using patch-clamp recording. Measurement of the dissociated neurons revealed that PG neurons were significantly larger than GG neurons. The active and passive membrane properties of these ganglion neurons were examined and compared with each other. There were significant differences between the properties of neurons in the PG and GG ganglia. The mean membrane time constant, spike threshold, action potential half-width, and action potential decay time of GG neurons was significantly less than those of PG neurons. Neurons in the PG had action potentials that had a fast rise and fall time (sharp action potentials) as well as action potentials with a deflection or hump on the falling phase (humped action potentials), whereas action potentials of GG neurons were all sharp. There were also significant differences in the response of PG and GG neurons to the application of acetylcholine (ACh), serotonin (5HT), substance P (SP), and GABA. Whereas PG neurons responded to ACh, 5HT, SP, and GABA, GG neurons only responded to SP and GABA. In addition, the properties of GG neurons were more homogeneous than those of the PG because all the GG neurons had sharp spikes and when responses to neurotransmitters occurred, either all or most of the neurons responded. These differences between neurons of the GG and PG may relate to the type of receptor innervated. PG ganglion neurons innervate a number of receptor types on the posterior tongue and have more heterogeneous properties, while GG neurons predominantly innervate taste buds and have more homogeneous properties.

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Modulatory effects of 5-hydroxytryptamine on voltage-activated currents in cultured antennal lobe neurones of the sphinx moth Manduca sexta.

Journal of Experimental Biology ◽

10.1242/jeb.198.3.613 ◽

1995 ◽

Vol 198 (3) ◽

pp. 613-627 ◽

Cited By ~ 2

Author(s):

A R Mercer ◽

J H Hayashi ◽

J G Hildebrand

Keyword(s):

Manduca Sexta ◽

Adult Development ◽

Antennal Lobe ◽

Ionic Currents ◽

Delayed Rectifier ◽

Patch Clamp Recording ◽

Whole Cell Patch Clamp ◽

K Current ◽

Reversible Reduction

The modulatory effects of 5-hydroxytryptamine (5-HT or serotonin) on voltage-gated currents in central olfactory neurones of the moth Manduca sexta have been examined in vitro using whole-cell patch-clamp recording techniques. Central olfactory neurones were dissociated from the antennal lobes of animals at stage 5 of the 18 stages of metamorphic adult development. The modulatory actions of 5-HT on voltage-activated ionic currents were examined in a subset of morphologically identifiable antennal lobe neurones maintained for 2 weeks in primary cell culture. 5-HT caused reversible reduction of both a rapidly activating A-type K+ current and a relatively slowly activating K+ current resembling a delayed rectifier-type conductance. 5-HT also reduced the magnitude of voltage-activated Ca2+ influx in these cells. The functional significance of 5-HT-modulation of central neurones is discussed.

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