K currents in ventricular cardiomyocytes of p.N98S-calmodulin mutant mice.

Missense mutations in calmodulin (CaM)-encoding genes are associated with life-threatening ventricular arrhythmia syndromes. Here, we investigated a role of cardiac K channel dysregulation in arrhythmogenic long QT syndrome (LQTS) using a knock-in mouse model heterozygous for a recurrent mutation (p.N98S) in the gene (Calm1).

Antisense Oligonucleotide Therapy for Calmodulinopathy.

Background: Calmodulinopathies are rare inherited arrhythmia syndromes caused by dominant heterozygous variants in , , or , which each encode the identical CaM (calmodulin) protein. We hypothesized that antisense oligonucleotide (ASO)-mediated depletion of an affected calmodulin gene would ameliorate disease manifestations, whereas the other 2 calmodulin genes would preserve CaM level and function.

Methods: We tested this hypothesis using human induced pluripotent stem cell-derived cardiomyocyte and mouse models of pathogenic variants.

Microparticle Mediated Delivery of Apelin Improves Heart Function in Post Myocardial Infarction Mice.

Background: Apelin is an endogenous prepropeptide that regulates cardiac homeostasis and various physiological processes. Intravenous injection has been shown to improve cardiac contractility in patients with heart failure. However, its short half-life prevents studying its impact on left ventricular remodeling in the long term.

A Barth Syndrome Patient-Derived Point Mutation in Drives Progressive Cardiomyopathy in Mice.

Cardiomyopathy is the predominant defect in Barth syndrome (BTHS) and is caused by a mutation of the X-linked gene, which encodes an enzyme responsible for remodeling mitochondrial cardiolipin. Despite the known importance of mitochondrial dysfunction in BTHS, how specific mutations cause diverse BTHS heart phenotypes remains poorly understood. We generated a patient-tailored knock-in mouse allele () that phenocopies BTHS clinical traits.

Neonatal Deletion of and within Murine Cardiac Conduction System Reveals a Novel Role for HAND2 in Rhythm Homeostasis.

The cardiac conduction system, a network of specialized cells, is required for the functioning of the heart. The basic helix loop helix factors and are required for cardiac morphogenesis and have been implicated in cardiac conduction system development and maintenance. Here we use embryonic and post-natal specific lines to interrogate the role of and in the function of the murine cardiac conduction system.

Testosterone does not shorten action potential duration in Langendorff-perfused rabbit ventricles.

Background: Women have longer baseline QT intervals than men. Because previous studies showed that testosterone and 5α-dihydrotestosterone shorten the ventricular action potential duration (APD) in animal models, differential testosterone concentrations may account for the sex differences in QT interval.

Objective: The purpose of this study was to test the hypothesis that testosterone shortens the APD in Langendorff-perfused rabbit ventricles.

Optogenetic Control of Engrafted Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes in Live Mice: A Proof-of-Concept Study.

Background: Cellular transplantation has emerged as promising approach for treating cardiac diseases. However, a poor engraftment rate limits our understanding on how transplanted cardiomyocytes contribute to cardiac function in the recipient’s heart. Methods: The CRISPR/Cas9 technique was employed for stable and constitutive gene expression in human-induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs).

Calmodulinopathy in inherited arrhythmia syndromes.

Calmodulin (CaM) is a ubiquitous intracellular calcium sensor that controls and regulates key cellular functions. In all vertebrates, three CaM genes located on separate chromosomes encode an identical 149 amino acid protein, implying an extraordinarily high level of evolutionary importance and suggesting that CaM mutations would be possibly fatal. Inherited arrhythmia syndromes comprise a spectrum of primary electrical disorders caused by mutations in genes encoding ion channels or associated proteins leading to various cardiac arrhythmias, unexplained syncope, and sudden cardiac death.

Inhibition of Small-Conductance, Ca-Activated K Current by Ondansetron.

Small-conductance Ca-activated K channels (SK channels) have been proposed as antiarrhythmic targets for the treatment of atrial fibrillation. We previously demonstrated that the 5-HT receptor antagonist ondansetron inhibits heterologously expressed, human SK2 (hSK2) currents as well as native cardiac SK currents in a physiological extra-/intracellular [K] gradient at therapeutic (i.e.

Complex Arrhythmia Syndrome in a Knock-In Mouse Model Carrier of the N98S Mutation.

Background: Calmodulin mutations are associated with arrhythmia syndromes in humans. Exome sequencing previously identified a de novo mutation in resulting in a p.N98S substitution in a patient with sinus bradycardia and stress-induced bidirectional ventricular ectopy.

Sex-specific I activation in rabbit ventricles with drug-induced QT prolongation.

Background: Female sex is a known risk factor for drug-induced long QT syndrome (diLQTS). We recently demonstrated a sex difference in apamin-sensitive small-conductance Ca-activated K current (I) activation during β-adrenergic stimulation.

Objective: The purpose of this study was to test the hypothesis that there is a sex difference in I in the rabbit models of diLQTS.

Optogenetics: Background, Methodological Advances and Potential Applications for Cardiovascular Research and Medicine.

Optogenetics is an elegant approach of precisely controlling and monitoring the biological functions of a cell, group of cells, tissues, or organs with high temporal and spatial resolution by using optical system and genetic engineering technologies. The field evolved with the need to precisely control neurons and decipher neural circuity and has made great accomplishments in neuroscience. It also evolved in cardiovascular research almost a decade ago and has made considerable progress in both and animal studies.

Cardiac sympathetic innervation network shapes the myocardium by locally controlling cardiomyocyte size through the cellular proteolytic machinery.

Key Points: The heart is innervated by a dense sympathetic neuron network which, in the short term, controls chronotropy and inotropy and, in the long term, regulates cardiomyocyte size. Acute neurogenic control of heart rate is achieved locally through direct neuro-cardiac coupling at specific junctional sites (neuro-cardiac junctions). The ventricular sympathetic network topology is well-defined and characteristic for each mammalian species.

Atrial fibrillation and electrophysiology in transgenic mice with cardiac-restricted overexpression of FKBP12.

Cardiomyocyte-restricted overexpression of FK506-binding protein 12 transgenic (αMyHC-FKBP12) mice develop spontaneous atrial fibrillation (AF). The aim of the present study is to explore the mechanisms underlying the occurrence of AF in αMyHC-FKBP12 mice. Spontaneous AF was documented by telemetry in vivo and Langendorff-perfused hearts of αMyHC-FKBP12 and littermate control mice in vitro.

Ondansetron blocks wild-type and p.F503L variant small-conductance Ca-activated K channels.

Apamin-sensitive small-conductance Ca-activated K (SK) current ( I) is encoded by Ca-activated K channel subfamily N ( KCNN) genes. I importantly contributes to cardiac repolarization in conditions associated with reduced repolarization reserve. To test the hypothesis that I inhibition contributes to drug-induced long QT syndrome (diLQTS), we screened for KCNN variants among patients with diLQTS, determined the properties of heterologously expressed wild-type (WT) and variant KCNN channels, and determined if the 5-HT receptor antagonist ondansetron blocks I.

Electrical coupling between ventricular myocytes and myofibroblasts in the infarcted mouse heart.

Aims: Recent studies have demonstrated electrotonic coupling between scar tissue and the surrounding myocardium in cryoinjured hearts. However, the electrical dynamics occurring at the myocyte-nonmyocyte interface in the fibrotic heart remain undefined. Here, we sought to develop an assay to interrogate the nonmyocyte cell type contributing to heterocellular coupling and to characterize, on a cellular scale, its voltage response in the infarct border zone of living hearts.

Small-Conductance Calcium-Activated Potassium Current in Normal Rabbit Cardiac Purkinje Cells.

Background: Purkinje cells (PCs) are important in cardiac arrhythmogenesis. Whether small-conductance calcium-activated potassium (SK) channels are present in PCs remains unclear. We tested the hypotheses that subtype 2 SK (SK2) channel proteins and apamin-sensitive SK currents are abundantly present in PCs.

Arrhythmogenic calmodulin mutations impede activation of small-conductance calcium-activated potassium current.

Background: Apamin-sensitive small-conductance calcium-activated potassium (SK) channels are gated by intracellular Ca(2+) through a constitutive interaction with calmodulin.

Objective: We hypothesize that arrhythmogenic human calmodulin mutations impede activation of SK channels.

Methods: We studied 5 previously published calmodulin mutations (N54I, N98S, D96V, D130G, and F90L).

Voltage-Induced Ca²⁺ Release in Postganglionic Sympathetic Neurons in Adult Mice.

Recent studies have provided evidence that depolarization in the absence of extracellular Ca2+ can trigger Ca2+ release from internal stores in a variety of neuron subtypes. Here we examine whether postganglionic sympathetic neurons are able to mobilize Ca2+ from intracellular stores in response to depolarization, independent of Ca2+ influx. We measured changes in cytosolic ΔF/F0 in individual fluo-4 -loaded sympathetic ganglion neurons in response to maintained K+ depolarization in the presence (2 mM) and absence of extracellular Ca2+ ([Ca2+]e).

Critical Roles of STAT3 in β-Adrenergic Functions in the Heart.

Background: β-Adrenergic receptors (βARs) play paradoxical roles in the heart. On one hand, βARs augment cardiac performance to fulfill the physiological demands, but on the other hand, prolonged activations of βARs exert deleterious effects that result in heart failure. The signal transducer and activator of transcription 3 (STAT3) plays a dynamic role in integrating multiple cytokine signaling pathways in a number of tissues.

Small-Conductance Calcium-Activated Potassium Current Is Activated During Hypokalemia and Masks Short-Term Cardiac Memory Induced by Ventricular Pacing.

Background: Hypokalemia increases the vulnerability to ventricular fibrillation. We hypothesize that the apamin-sensitive small-conductance calcium-activated potassium current (IKAS) is activated during hypokalemia and that IKAS blockade is proarrhythmic.

Methods And Results: Optical mapping was performed in 23 Langendorff-perfused rabbit ventricles with atrioventricular block and either right or left ventricular pacing during normokalemia or hypokalemia.