Divergent regulation of KCNQ1/E1 by targeted recruitment of protein kinase A to distinct sites on the channel complex.

The slow delayed rectifier potassium current, , conducted through pore-forming Q1 and auxiliary E1 ion channel complexes is important for human cardiac action potential repolarization. During exercise or fright, is up-regulated by protein kinase A (PKA)-mediated Q1 phosphorylation to maintain heart rhythm and optimum cardiac performance. Sympathetic up-regulation of requires recruitment of PKA holoenzyme (two regulatory - RI or RII - and two catalytic Cα subunits) to Q1 C-terminus by an A kinase anchoring protein (AKAP9).

Pharmacological rescue of specific long QT variants of KCNQ1/KCNE1 channels.

The congenital Long QT Syndrome (LQTS) is an inherited disorder in which cardiac ventricular repolarization is delayed and predisposes patients to cardiac arrhythmias and sudden cardiac death. LQT1 and LQT5 are LQTS variants caused by mutations in KCNQ1 or KCNE1 genes respectively. KCNQ1 and KCNE1 co-assemble to form critical I potassium channels.

Potassium Channels as Therapeutic Targets in Pulmonary Arterial Hypertension.

Pulmonary arterial hypertension (PAH) is a devastating disease with high morbidity and mortality. Deleterious remodeling in the pulmonary arterial system leads to irreversible arterial constriction and elevated pulmonary arterial pressures, right heart failure, and eventually death. The difficulty in treating PAH stems in part from the complex nature of disease pathogenesis, with several signaling compounds known to be involved (e.

Two small-molecule activators share similar effector sites in the KCNQ1 channel pore but have distinct effects on voltage sensor movements.

ML277 and R-L3 are two small-molecule activators of KCNQ1, the pore-forming subunit of the slowly activating potassium channel I. KCNQ1 loss-of-function mutations prolong cardiac action potential duration and are associated with long QT syndrome, which predispose patients to lethal ventricular arrhythmia. ML277 and R-L3 enhance KCNQ1 current amplitude and slow deactivation.

Exploring mutation specific beta blocker pharmacology of the pathogenic late sodium channel current from patient-specific pluripotent stem cell myocytes derived from long QT syndrome mutation carriers.

The congenital long QT syndrome (LQTS), one of the most common cardiac channelopathies, is characterized by delayed ventricular repolarization underlying prolongation of the QT interval of the surface electrocardiogram. LQTS is caused by mutations in genes coding for cardiac ion channels or ion channel-associated proteins. The major therapeutic approach to LQTS management is beta blocker therapy which has been shown to be effective in treatment of LQTS variants caused by mutations in K channels.

Human iPSC-derived cardiomyocytes and pyridyl-phenyl mexiletine analogs.

In the United States, approximately one million individuals are hospitalized every year for arrhythmias, making arrhythmias one of the top causes of healthcare expenditures. Mexiletine is currently used as an antiarrhythmic drug but has limitations. The purpose of this work was to use normal and Long QT syndrome Type 3 (LQTS3) patient-derived human induced pluripotent stem cell (iPSC)-derived cardiomyocytes to identify an analog of mexiletine with superior drug-like properties.

Antiarrhythmic Hit to Lead Refinement in a Dish Using Patient-Derived iPSC Cardiomyocytes.

Ventricular cardiac arrhythmia (VA) arises in acquired or congenital heart disease. Long QT syndrome type-3 (LQT3) is a congenital form of VA caused by cardiac sodium channel (I) SCN5A mutations that prolongs cardiac action potential (AP) and enhances I current. Mexiletine inhibits I and shortens the QT interval in LQT3 patients.

Reengineering an Antiarrhythmic Drug Using Patient hiPSC Cardiomyocytes to Improve Therapeutic Potential and Reduce Toxicity.

Modeling cardiac disorders with human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes is a new paradigm for preclinical testing of candidate therapeutics. However, disease-relevant physiological assays can be complex, and the use of hiPSC-cardiomyocyte models of congenital disease phenotypes for guiding large-scale screening and medicinal chemistry have not been shown. We report chemical refinement of the antiarrhythmic drug mexiletine via high-throughput screening of hiPSC-CMs derived from patients with the cardiac rhythm disorder long QT syndrome 3 (LQT3) carrying SCN5A sodium channel variants.

Loss-of-Function ABCC8 Mutations in Pulmonary Arterial Hypertension.

Background: In pulmonary arterial hypertension (PAH), pathological changes in pulmonary arterioles progressively raise pulmonary artery pressure and increase pulmonary vascular resistance, leading to right heart failure and high mortality rates. Recently, the first potassium channelopathy in PAH, because of mutations in KCNK3, was identified as a genetic cause and pharmacological target.

Methods: Exome sequencing was performed to identify novel genes in a cohort of 99 pediatric and 134 adult-onset group I PAH patients.

The Impact of Heterozygous Mutations Associated With Pulmonary Arterial Hypertension on Channel Function and Pharmacological Recovery.

Background: Heterozygous loss of function mutations in the gene cause hereditary pulmonary arterial hypertension (PAH). encodes an acid-sensitive potassium channel, which contributes to the resting potential of human pulmonary artery smooth muscle cells. KCNK3 is widely expressed in the body, and dimerizes with other KCNK3 subunits, or the closely related, acid-sensitive KCNK9 channel.

Gating mechanisms underlying deactivation slowing by two KCNQ1 atrial fibrillation mutations.

KCNQ1 is a voltage-gated potassium channel that is modulated by the beta-subunit KCNE1 to generate I, the slow delayed rectifier current, which plays a critical role in repolarizing the cardiac action potential. Two KCNQ1 gain-of-function mutations that cause a genetic form of atrial fibrillation, S140G and V141M, drastically slow I deactivation. However, the underlying gating alterations remain unknown.

Coupling Data Mining and Laboratory Experiments to Discover Drug Interactions Causing QT Prolongation.

Background: QT interval-prolonging drug-drug interactions (QT-DDIs) may increase the risk of life-threatening arrhythmia. Despite guidelines for testing from regulatory agencies, these interactions are usually discovered after drugs are marketed and may go undiscovered for years.

Objectives: Using a combination of adverse event reports, electronic health records (EHR), and laboratory experiments, the goal of this study was to develop a data-driven pipeline for discovering QT-DDIs.

Cardiac Delayed Rectifier Potassium Channels in Health and Disease.

Cardiac delayed rectifier potassium channels conduct outward potassium currents during the plateau phase of action potentials and play pivotal roles in cardiac repolarization. These include IKs, IKr and the atrial specific IKur channels. In this article, we will review their molecular identities and biophysical properties.

An Integrative Data Science Pipeline to Identify Novel Drug Interactions that Prolong the QT Interval.

Introduction: Drug-induced prolongation of the QT interval on the electrocardiogram (long QT syndrome, LQTS) can lead to a potentially fatal ventricular arrhythmia known as torsades de pointes (TdP). Over 40 drugs with both cardiac and non-cardiac indications are associated with increased risk of TdP, but drug-drug interactions contributing to LQTS (QT-DDIs) remain poorly characterized. Traditional methods for mining observational healthcare data are poorly equipped to detect QT-DDI signals due to low reporting numbers and lack of direct evidence for LQTS.

Purkinje Cells as Sources of Arrhythmias in Long QT Syndrome Type 3.

Long QT syndrome (LQTS) is characterized by ventricular arrhythmias and sudden cardiac death. Purkinje cells (PC) within the specialized cardiac conduction system have unique electrophysiological properties that we hypothesize may produce the primary sources of arrhythmia in heritable LQTS. LQTS type 3 (LQT3) transgenic mice harboring the ΔKPQ(+/-) mutation were crossed with Contactin2-EGFP BAC transgenic mice, which express a fluorescent reporter gene within the Purkinje fiber network.

Modeling tissue- and mutation- specific electrophysiological effects in the long QT syndrome: role of the Purkinje fiber.

Congenital long QT syndrome is a heritable family of arrhythmias caused by mutations in 13 genes encoding ion channel complex proteins. Mounting evidence has implicated the Purkinje fiber network in the genesis of ventricular arrhythmias. In this study, we explore the hypothesis that long QT mutations can demonstrate different phenotypes depending on the tissue type of expression.

KCNE1 divides the voltage sensor movement in KCNQ1/KCNE1 channels into two steps.

The functional properties of KCNQ1 channels are highly dependent on associated KCNE-β subunits. Mutations in KCNQ1 or KCNE subunits can cause congenital channelopathies, such as deafness, cardiac arrhythmias and epilepsy. The mechanism by which KCNE1-β subunits slow the kinetics of KCNQ1 channels is a matter of current controversy.

Unique cardiac Purkinje fiber transient outward current β-subunit composition: a potential molecular link to idiopathic ventricular fibrillation.

Rationale: A chromosomal haplotype producing cardiac overexpression of dipeptidyl peptidase-like protein-6 (DPP6) causes familial idiopathic ventricular fibrillation. The molecular basis of transient outward current (I(to)) in Purkinje fibers (PFs) is poorly understood. We hypothesized that DPP6 contributes to PF I(to) and that its overexpression might specifically alter PF I(to) properties and repolarization.

Induced pluripotent stem cells used to reveal drug actions in a long QT syndrome family with complex genetics.

Understanding the basis for differential responses to drug therapies remains a challenge despite advances in genetics and genomics. Induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to investigate the pharmacology of disease processes in therapeutically and genetically relevant primary cell types in vitro and to interweave clinical and basic molecular data. We report here the derivation of iPSCs from a long QT syndrome patient with complex genetics.

Allosteric gating mechanism underlies the flexible gating of KCNQ1 potassium channels.

KCNQ1 (Kv7.1) is a unique member of the superfamily of voltage-gated K(+) channels in that it displays a remarkable range of gating behaviors tuned by coassembly with different β subunits of the KCNE family of proteins. To better understand the basis for the biophysical diversity of KCNQ1 channels, we here investigate the basis of KCNQ1 gating in the absence of β subunits using voltage-clamp fluorometry (VCF).

Perturbation of sodium channel structure by an inherited Long QT Syndrome mutation.

The cardiac voltage-gated sodium channel (Na(V)1.5) underlies impulse conduction in the heart, and its depolarization-induced inactivation is essential in control of the duration of the QT interval of the electrocardiogram. Perturbation of Na(V)1.

Characterization of KCNQ1 atrial fibrillation mutations reveals distinct dependence on KCNE1.

The I(Ks) potassium channel, critical to control of heart electrical activity, requires assembly of α (KCNQ1) and β (KCNE1) subunits. Inherited mutations in either I(Ks) channel subunit are associated with cardiac arrhythmia syndromes. Two mutations (S140G and V141M) that cause familial atrial fibrillation (AF) are located on adjacent residues in the first membrane-spanning domain of KCNQ1, S1.

Biophysical properties of slow potassium channels in human embryonic stem cell derived cardiomyocytes implicate subunit stoichiometry.

Human embryonic stem cells (hESCs) are an important cellular model for studying ion channel function in the context of a human cardiac cell and will provide a wealth of information about both heritable arrhythmias and acquired electrophysiological disorders. However, detailed electrophysiological characterization of the important cardiac ion channels has been so far overlooked. Because mutations in the gene for the I(Ks) α subunit, KCNQ1, constitute the majority of long QT syndrome (LQT-1) cases, we have carried out a detailed biophysical analysis of this channel expressed in hESCs to establish baseline I(Ks) channel biophysical properties in cardiac myocytes derived from hESCs (hESC-CMs).

KCNE1 alters the voltage sensor movements necessary to open the KCNQ1 channel gate.

The delayed rectifier I(Ks) potassium channel, formed by coassembly of α- (KCNQ1) and β- (KCNE1) subunits, is essential for cardiac function. Although KCNE1 is necessary to reproduce the functional properties of the native I(Ks) channel, the mechanism(s) through which KCNE1 modulates KCNQ1 is unknown. Here we report measurements of voltage sensor movements in KCNQ1 and KCNQ1/KCNE1 channels using voltage clamp fluorometry.