A generic binding pocket for small molecule activators at the extracellular inter-subunit interface of KCNQ1 and KCNE1 channel complexes.

The cardiac ion channel comprises KCNQ1, calmodulin, and KCNE1 in a dodecameric complex which provides a repolarizing current reserve at higher heart rates and protects from arrhythmia syndromes that cause fainting and sudden death. Pharmacological activators of are therefore of interest both scientifically and therapeutically for treatment of loss-of-function disorders. One group of chemical activators are only active in the presence of the accessory KCNE1 subunit and here we investigate this phenomenon using molecular modeling techniques and mutagenesis scanning in mammalian cells.

Effects of Electrical Stimulation on hiPSC-CM Responses to Classic Ion Channel Blockers.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) hold great potential for personalized cardiac safety prediction, particularly for that of drug-induced proarrhythmia. However, hiPSC-CMs fire spontaneously and the variable beat rates of cardiomyocytes can be a confounding factor that interferes with data interpretation. Controlling beat rates with pacing may reduce batch and assay variations, enable evaluation of rate-dependent drug effects, and facilitate the comparison of results obtained from hiPSC-CMs with those from adult human cardiomyocytes.

The Emergence of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs) as a Platform to Model Arrhythmogenic Diseases.

There is a need for improved in vitro models of inherited cardiac diseases to better understand basic cellular and molecular mechanisms and advance drug development. Most of these diseases are associated with arrhythmias, as a result of mutations in ion channel or ion channel-modulatory proteins. Thus far, the electrophysiological phenotype of these mutations has been typically studied using transgenic animal models and heterologous expression systems.

Cardiac Ryanodine Receptor (Ryr2)-mediated Calcium Signals Specifically Promote Glucose Oxidation via Pyruvate Dehydrogenase.

Cardiac ryanodine receptor (Ryr2) Ca release channels and cellular metabolism are both disrupted in heart disease. Recently, we demonstrated that total loss of Ryr2 leads to cardiomyocyte contractile dysfunction, arrhythmia, and reduced heart rate. Acute total Ryr2 ablation also impaired metabolism, but it was not clear whether this was a cause or consequence of heart failure.

The interaction between delayed rectifier channel alpha-subunits does not involve hetero-tetramer formation.

We have previously reported a physiologically relevant interaction between KCNQ1 (Q1) and KCNH2 (H2). While the H2 C-terminus has been suggested to play a role, so far, no more detailed information regarding the interaction site is available. The methods used in the study are cell culture, PCR for mutagenesis, patch clamp for ion current recordings, co-immunoprecipitation for determination of protein interaction.

Ranolazine improves diastolic function in spontaneously hypertensive rats.

Diastolic dysfunction can lead to heart failure with preserved ejection fraction, for which there is no effective therapeutic. Ranolazine has been reported to reduce diastolic dysfunction, but the specific mechanisms of action are unclear. The effect of ranolazine on diastolic function was examined in spontaneously hypertensive rats (SHRs), where left ventricular relaxation is impaired and stiffness increased.

The new antiarrhythmic drug vernakalant: ex vivo study of human atrial tissue from sinus rhythm and chronic atrial fibrillation.

Aims: Vernakalant is a newly developed antiarrhythmic drug against atrial fibrillation (AF). However, its electrophysiological actions on human myocardium are unknown.

Methods And Results: Action potentials (APs) and ion currents were recorded in right atrial trabeculae and cardiomyocytes from patients in sinus rhythm (SR) and chronic AF.

Rate-dependent effects of vernakalant in the isolated non-remodeled canine left atria are primarily due to block of the sodium channel: comparison with ranolazine and dl-sotalol.

Background: Several clinical trials have shown that vernakalant is effective in terminating recent onset atrial fibrillation (AF). The electrophysiological actions of vernakalant are not fully understood.

Methods And Results: Here we report the results of a blinded study comparing the in vitro canine atrial electrophysiological effects of vernakalant, ranolazine, and dl-sotalol.

Comparison of electrophysiological and antiarrhythmic effects of vernakalant, ranolazine, and sotalol in canine pulmonary vein sleeve preparations.

Background: Vernakalant (VER) is a relatively atrial-selective antiarrhythmic drug capable of blocking potassium and sodium currents in a frequency- and voltage-dependent manner. Ranolazine (RAN) is a sodium-channel blocker shown to exert antiarrhythmic effects in pulmonary vein (PV) sleeves. dl-Sotalol (SOT) is a β-blocker commonly used in the rhythm-control treatment of atrial fibrillation.

Atrial selective effects of intravenously administered vernakalant in conscious beagle dogs.

Vernakalant is a relatively atrial-selective antiarrhythmic drug approved for the conversion of recent onset atrial fibrillation in Europe and is under regulatory review in the United States. In this study, we examined the effects of intravenously administered vernakalant (5, 10, and 20 mg/kg) on blood pressure, heart rate, and the electrocardiogram in conscious male beagle dogs and compared them with those of orally administered dl-sotalol (32 mg/kg). Vernakalant had no consistent dose-dependent effects on the heart rate or mean arterial pressure.

Comparison of the in vivo hemodynamic effects of the antiarrhythmic agents vernakalant and flecainide in a rat hindlimb perfusion model.

A series of in vivo experiments were conducted to compare the hemodynamic actions of vernakalant (a novel, relatively atrial selective, antiarrhythmic drug) to flecainide after infusion into the peripheral vasculature. Anesthetized rats were surgically prepared to have an extracorporeal perfusion circuit whereby blood in the abdominal aorta (distal to the renal arteries) was diverted to a constant flow pump and returned to the abdominal aorta at the same level allowing measurement of hindlimb vascular resistance. The effects of cumulative, ascending doses of intravenous vernakalant and flecainide on vascular resistance, after arterial pressures, and heart rate were measured.

Comparison of ion channel distribution and expression in cardiomyocytes of canine pulmonary veins versus left atrium.

Background: Cardiomyocytes in pulmonary vein (PV) sleeves are important in atrial fibrillation (AF), but underlying mechanisms are poorly understood. Pulmonary veins have different ionic current properties compared to left atrium, with pulmonary vein inward-rectifier currents being smaller and delayed-rectifier currents larger than in left atrium.

Methods: Expression and distribution of the inward-rectifier subunits Kir2.

The Kv4.2 N-terminal restores fast inactivation and confers KChlP2 modulatory effects on N-terminal-deleted Kv1.4 channels.

The N-terminal end of the subunits of the voltage-gated K+ channel Kv1.4 is essential for their rapid N-type inactivation, but removal of the entire Kv4.2 N-terminus slows inactivation only moderately.

[Anchoring proteins and cardiac sudden death: how and why?].

Mutations in proteins responsible for ion transport in cardiac tissue can induce a destabilization of electrical function and provoke cardiac sudden death. Identification of a genetic anomaly in a French family that developed the syndrome of cardiac sudden death has revealed a crucial new element in normal cardiac electrical function : Ion channels need to be anchored to specific domains at the plasma membrane by an anchoring protein called ankyrin-B.

KvLQT1 modulates the distribution and biophysical properties of HERG. A novel alpha-subunit interaction between delayed rectifier currents.

Cardiac repolarization is under joint control of the slow (IKs) and rapid (IKr) delayed rectifier currents. Experimental and clinical evidence indicates important functional interactions between these components. We hypothesized that there might be more direct interactions between the KvLQT1 and HERG alpha-subunits of IKs and IKr and tested this notion with a combination of biophysical and biochemical techniques.

Barium block of Kir2 and human cardiac inward rectifier currents: evidence for subunit-heteromeric contribution to native currents.

Background: Kir2 subunits are believed to underlie the cardiac inwardly rectifying current I(K1). The subunit composition of native I(K1) currents is uncertain, and it has been suggested that heteromultimer formation may play a role.

Methods: We studied Ba(2+) block of homo- and heteromeric Kir2 channels in Xenopus oocytes and compared the properties observed to those of human cardiac I(K1) in cells isolated from myocardial biopsies of normal human hearts.

Canine ventricular KCNE2 expression resides predominantly in Purkinje fibers.

Mutations in minK-related peptide 1 (MiRP1), the product of the KCNE2 gene, have been associated with malignant ventricular arrhythmia syndromes related to impaired repolarization. MiRP1 interacts with a variety of ion-channel alpha-subunits, dysfunction of which could account for arrhythmia syndromes; however, the observation of very low-level expression of MiRP1 in ventricular tissue has led to doubts about its relevance. The specialized His-Purkinje system plays a key role in cardiac electrophysiology and is an important contributor to ventricular arrhythmias related to abnormal repolarization.

Effects of flecainide and quinidine on Kv4.2 currents: voltage dependence and role of S6 valines.

1. The effects of flecainide and quinidine were studied on wild-type Kv4.2 channels (Kv4.

Kir2.4 and Kir2.1 K(+) channel subunits co-assemble: a potential new contributor to inward rectifier current heterogeneity.

Heteromeric channel assembly is a potential source of physiological variability. The potential significance of Kir2 subunit heterotetramerization has been controversial, but recent findings suggest that heteromultimerization of Kir2.1-3 may be significant.

Differential distribution of cardiac ion channel expression as a basis for regional specialization in electrical function.

The cardiac electrical system is designed to ensure the appropriate rate and timing of contraction in all regions of the heart, which are essential for effective cardiac function. Well-controlled cardiac electrical activity depends on specialized properties of various components of the system, including the sinoatrial node, atria, atrioventricular node, His-Purkinje system, and ventricles. Cardiac electrical specialization was first recognized in the mid 1800s, but over the past 15 years, an enormous amount has been learned about how specialization is achieved by differential expression of cardiac ion channels.