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Journal ArticleDOI

hERG1a and hERG1b potassium channel subunits directly interact and preferentially form heteromeric channels

29 Dec 2017-Journal of Biological Chemistry (American Society for Biochemistry and Molecular Biology)-Vol. 292, Iss: 52, pp 21548-21557
TL;DR: HERG1b preferentially forms heteromeric ion channels with hERG1a at the plasma membrane, and multiple lines of evidence indicated a physical interaction between hERG 1a and hERG2b, consistent with them forming heteromerics channels.
About: This article is published in Journal of Biological Chemistry.The article was published on 2017-12-29 and is currently open access. It has received 19 citations till now. The article focuses on the topics: Ion channel & Potassium channel.
Citations
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Journal ArticleDOI
TL;DR: In an effort to encapsulate the breadth over which fluorescent biosensors have expanded, this work endeavored to assemble a comprehensive list of published engineered bios Sensors, and discusses many of the molecular designs utilized in their development.
Abstract: Cellular signaling networks are the foundation which determines the fate and function of cells as they respond to various cues and stimuli. The discovery of fluorescent proteins over 25 years ago enabled the development of a diverse array of genetically encodable fluorescent biosensors that are capable of measuring the spatiotemporal dynamics of signal transduction pathways in live cells. In an effort to encapsulate the breadth over which fluorescent biosensors have expanded, we endeavored to assemble a comprehensive list of published engineered biosensors, and we discuss many of the molecular designs utilized in their development. Then, we review how the high temporal and spatial resolution afforded by fluorescent biosensors has aided our understanding of the spatiotemporal regulation of signaling networks at the cellular and subcellular level. Finally, we highlight some emerging areas of research in both biosensor design and applications that are on the forefront of biosensor development.

313 citations

Journal ArticleDOI
TL;DR: This primer reviews the clinical implications of a drug's identified proarrhythmic liability, the issues associated with these safety‐related withdrawals, and the actions taken by the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) and by regulatory agencies in terms of changing drug development practices and introducing new nonclinical and clinical tests to asses proarrhalic liability.
Abstract: Multiple marketing withdrawals due to proarrhythmic concerns occurred in the United States, Canada, and the United Kingdom in the late 1980s to early 2000s. This primer reviews the clinical implications of a drug's identified proarrhythmic liability, the issues associated with these safety-related withdrawals, and the actions taken by the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) and by regulatory agencies in terms of changing drug development practices and introducing new nonclinical and clinical tests to asses proarrhythmic liability. ICH Guidelines S7B and E14 were released in 2005. Since then, they have been adopted by many regional regulatory authorities and have guided nonclinical and clinical proarrhythmic cardiac safety assessments during drug development. While this regulatory paradigm has been successful in preventing drugs with unanticipated potential for inducing the rare but potentially fatal polymorphic ventricular arrhythmia torsade de pointes from entering the market, it has led to the termination of drug development programs for other potentially useful medicines because of isolated results from studies with limited predictive value. Research efforts are now exploring alternative approaches to better predict potential proarrhythmic liabilities. For example, in the domain of human electrocardiographic assessments, concentration-response modeling conducted during phase 1 clinical development has recently become an accepted alternate primary methodology to the ICH E14 "thorough QT/QTc" study for defining a drug's corrected QT interval prolongation liability under certain conditions. When a drug's therapeutic benefit is considered important at a public health level but there is also an identified proarrhythmic liability that may result from administration of the single drug in certain individuals and/or drug-drug interactions, marketing approval will be accompanied by appropriate directions in the drug's prescribing information. Health-care professionals in the fields of medicine and pharmacy need to consider the prescribing information in conjunction with individual patients' clinical characteristics and concomitant medications when prescribing and dispensing such drugs.

28 citations

Journal ArticleDOI
31 Oct 2019-eLife
TL;DR: It is found that roughly half the hERG translational complexes contain SCN5A transcripts, and association and coordinate regulation of transcripts in discrete ‘microtranslatomes’ represents a new paradigm controlling electrical activity in heart and other excitable tissues.
Abstract: Catastrophic arrhythmias and sudden cardiac death can occur with even a small imbalance between inward sodium currents and outward potassium currents, but mechanisms establishing this critical balance are not understood. Here, we show that mRNA transcripts encoding INa and IKr channels (SCN5A and hERG, respectively) are associated in defined complexes during protein translation. Using biochemical, electrophysiological and single-molecule fluorescence localization approaches, we find that roughly half the hERG translational complexes contain SCN5A transcripts. Moreover, the transcripts are regulated in a way that alters functional expression of both channels at the membrane. Association and coordinate regulation of transcripts in discrete 'microtranslatomes' represents a new paradigm controlling electrical activity in heart and other excitable tissues.

24 citations


Cites background from "hERG1a and hERG1b potassium channel..."

  • ...IKr channels minimally comprise hERG1a and hERG1b subunits (Sale et al., 2008; Jones et al., 2004), which associate cotranslationally (Phartiyal et al., 2007) and preferentially form heteromultimers (McNally et al., 2017)....

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Journal ArticleDOI
TL;DR: It is demonstrated that heterologously expressed human ether a-go-go–related gene (hERG) 1a/1b channels, which more closely resemble rapidly activating delayed rectifier potassium current in the human heart, are blocked by fentanyl with a 3-fold greater potency than the previously studied hERG1a expressed alone.
Abstract: Human ether-a-go-go-related gene (hERG) encodes the pore-forming subunit of the rapidly activating delayed rectifier potassium current (IKr) important for repolarization of cardiac action potentials. Drug-induced disruption of hERG channel function is a main cause of acquired long QT syndrome, which can lead to ventricular arrhythmias and sudden death. Illicit fentanyl use is associated with sudden death. We have demonstrated that fentanyl blocks hERG current (IhERG) at concentrations that overlap with the upper range of postmortem blood concentrations in fentanyl-related deaths. Since fentanyl can cause respiratory depression and electrolyte imbalances, in the present study we investigated whether certain pathologic circumstances exacerbate fentanyl-induced block of IhERG Our results show that chronic hypoxia or hypokalemia additively reduced IhERG with fentanyl. As well, high pH potentiated the fentanyl-mediated block of hERG channels, with an IC50 at pH 8.4 being 7-fold lower than that at pH 7.4. Furthermore, although the full-length hERG variant, hERG1a, has been widely used to study hERG channels, coexpression with the short variant, hERG1b (which does not produce current when expressed alone), produces functional hERG1a/1b channels, which gate more closely resembling native IKr Our results showed that fentanyl blocked hERG1a/1b channels with a 3-fold greater potency than hERG1a channels. Thus, in addition to a greater susceptibility due to the presence of hERG1b in the human heart, hERG channel block by fentanyl can be exacerbated by certain conditions, such as hypoxia, hypokalemia, or alkalosis, which may increase the risk of fentanyl-induced ventricular arrhythmias and sudden death. SIGNIFICANCE STATEMENT: This work demonstrates that heterologously expressed human ether a-go-go-related gene (hERG) 1a/1b channels, which more closely resemble rapidly activating delayed rectifier potassium current in the human heart, are blocked by fentanyl with a 3-fold greater potency than the previously studied hERG1a expressed alone. Additionally, chronic hypoxia, hypokalemia, and alkalosis can increase the block of hERG current by fentanyl, potentially increasing the risk of cardiac arrhythmias and sudden death.

8 citations

Journal ArticleDOI
TL;DR: In this paper, patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were derived from a LQT syndrome type 2 (LQT2) patient carrying the PAS domain variant hERG1-H70R.
Abstract: Background - Inherited long QT syndrome type 2 (LQT2) results from variants in the KCNH2 gene encoding the hERG1 potassium channel. Two main isoforms, hERG1a and hERG1b, assemble to form tetrameric channel. The N-terminal Per-Arnt-Sim (PAS) domain, present only on hERG1a subunits, is a hotspot for pathogenic variants, but it is unknown whether PAS domain variants impact hERG1b expression to contribute to the LQT2 phenotype. We aimed to use patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to investigate the pathogenesis of the hERG1a PAS domain variant hERG1-H70R. Methods - Human iPSCs were derived from a LQT2 patient carrying the PAS domain variant hERG1-H70R. CRISPR/Cas9 gene editing produced isogenic control iPSC lines. Differentiated iPSC-CMs were evaluated for their electrophysiology, hERG1a/1b mRNA expression, and hERG1a/1b protein expression. Results - Action potentials from single hERG1-H70R iPSC-CMs were prolonged relative to controls, and voltage clamp studies showed an underlying decrease in IKr with accelerated deactivation. In hERG1-H70R iPSC-CMs, transcription of hERG1a and hERG1b mRNA was unchanged compared to controls based on nascent nuclear transcript analysis, but hERG1b mRNA was significantly increased as was the ratio of hERG1b/hERG1a in mRNA complexes, suggesting post-transcriptional changes. Expression of complex glycosylated hERG1a in hERG1-H70R iPSC-CMs was reduced due to impaired protein trafficking, whereas the expression of the complex glycosylated form of hERG1b was unchanged. Conclusions - Patient-specific hERG1-H70R iPSC-CMs reveal a newly appreciated mechanism of pathogenesis of the LQT2 phenotype due to both impaired trafficking of hERG1a and maintained expression of hERG1b that produces subunit imbalance and reduced IKr with accelerated deactivation.

8 citations

References
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Journal ArticleDOI
21 Apr 1995-Cell
TL;DR: The finding that HERG encodes IKr channels provides a mechanistic link between certain forms of inherited and acquired LQT, and that an additional subunit may be required for drug sensitivity.

2,375 citations

Journal ArticleDOI
10 Mar 1995-Cell
TL;DR: In this article, the authors investigated patients with long QT syndrome (LQT), an inherited disorder causing sudden death from a ventricular tachyarrythmia, torsade de pointes.

2,207 citations


"hERG1a and hERG1b potassium channel..." refers background in this paper

  • ...Genetic mutations in both human ERG1a and ERG1b subunits are linked to LQT2 (1, 15, 16) indicating the pathophysiological importance of both isoforms. hERG1a and hERG1b are clearly both critical to form IKr and there is some evidence that the subunits co-associate....

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  • ...ERG K channels are expressed in the heart (1, 2), central nervous system (3), and in a variety of other tissues, including tumor cells (4, 5)....

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  • ...ERG1a and ERG1b subunits are linked to LQT2 (1, 15, 16) indi-...

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  • ...longed action potentials that can lead to sudden death (1)....

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Journal ArticleDOI
TL;DR: The results demonstrate that the production of more and better GFP variants is possible and worthwhile, and facilitates multicolor imaging of differential gene expression, protein localization or cell fate.

1,559 citations


"hERG1a and hERG1b potassium channel..." refers methods in this paper

  • ...Oocytes were injected with hERG channel subunits fused to monomeric, enhanced CFP or monomeric Citrine (26, 38)....

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01 Jan 1990
TL;DR: An envelope of tails test was used to show that the delayed rectifier K § current (Iv.) of guinea pig ventricular myocytes results from the activation of two outward K § currents as mentioned in this paper.
Abstract: An envelope of tails test was used to show that the delayed rectifier K § current (Iv.) of guinea pig ventricular myocytes results from the activation of two outward K § currents. One current was specifically blocked by the benzenesulfon- amide antiarrhythmic agent, E-4031 (IC50 = 397 nM). The drug-sensitive current, "I~" exhibits prominent rectification and activates very rapidly relative to the slowly activating drug-insensitive current, "Ivs." Iv, was characterized by a delayed onset of activation that occurs over a voltage range typical of the classically described cardiac I K. Fully activated Ivs, measured as tail current after 7.5-s test pulses, was 11.4 times larger than the fully activated I~. Ig r was also blocked by d-sotalol (100 #M), a less potent benzenesulfonamide Class III antiarrhythmic agent. The activation curve of lv~ had a steep slope (+7.5 mV) and a negative half-point (-21.5 mV) relative to the activation curve of Ivs (slope = + 12.7 mV, half-point = + 15.7 mV). The reversal potential (Erev) of I~ (-93 mV) was similar to EK (--94 mV for (K+)o ---- 4 mM), whereas Er~ of Ivs was -77 mV. The time constants for activation and deactivation of Iv~ made up a bell-shaped function of membrane potential, peaking between -30 and -40 mV (170 ms). The slope conductance of the linear portion of the fully activated Ig,-V relation was 22.5 S/F. Inward rectification of this relation occurred at potentials > -50 mV, resulting in a voltage-dependent decrease in peak Iv~ at test potentials > 0 InV. Peak Iw at 0 mV averaged 0.8 pA/pF (n ----- 21). Although the magnitude ofl~ was small relative to fully activated lw, the two currents were of similar magnitude when measured during a relatively short pulse protocol (225 ms) at membrane potentials (-20 to + 20 mV) typical of the plateau phase of cardiac action potentials.

1,387 citations

Journal ArticleDOI
TL;DR: The magnitude of IKr was small relative to fully activated IKs, and the two currents were of similar magnitude when measured during a relatively short pulse protocol at membrane potentials typical of the plateau phase of cardiac action potentials.
Abstract: An envelope of tails test was used to show that the delayed rectifier K+ current (IK) of guinea pig ventricular myocytes results from the activation of two outward K+ currents. One current was specifically blocked by the benzenesulfonamide antiarrhythmic agent, E-4031 (IC50 = 397 nM). The drug-sensitive current, "IKr" exhibits prominent rectification and activates very rapidly relative to the slowly activating drug-insensitive current, "IKs." IKs was characterized by a delayed onset of activation that occurs over a voltage range typical of the classically described cardiac IK. Fully activated IKs, measured as tail current after 7.5-s test pulses, was 11.4 times larger than the fully activated IKr. IKr was also blocked by d-sotalol (100 microM), a less potent benzenesulfonamide Class III antiarrhythmic agent. The activation curve of IKr had a steep slope (+7.5 mV) and a negative half-point (-21.5 mV) relative to the activation curve of IKs (slope = +12.7 mV, half-point = +15.7 mV). The reversal potential (Erev) of IKr (-93 mV) was similar to EK (-94 mV for [K+]o = 4 mM), whereas Erev of IKs was -77 mV. The time constants for activation and deactivation of IKr made up a bell-shaped function of membrane potential, peaking between -30 and -40 mV (170 ms). The slope conductance of the linear portion of the fully activated IKr-V relation was 22.5 S/F. Inward rectification of this relation occurred at potentials greater than -50 mV, resulting in a voltage-dependent decrease in peak IKr at test potentials greater than 0 mV. Peak IKr at 0 mV averaged 0.8 pA/pF (n = 21). Although the magnitude of IKr was small relative to fully activated IKs, the two currents were of similar magnitude when measured during a relatively short pulse protocol (225 ms) at membrane potentials (-20 to +20 mV) typical of the plateau phase of cardiac action potentials.

1,367 citations


"hERG1a and hERG1b potassium channel..." refers background in this paper

  • ...of IKr in adult mammalian cardiomyocytes (11, 12) and cardiomyocytes derived from human-induced pluripotent stem...

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  • ...cipal ( ) subunits that form the cardiac IKr current (2, 6 –10) whose role is to repolarize action potentials (11, 12)....

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