Cardiac ion channels

Cardiomyocyte regeneration after infarction: changes, opportunities and challenges

Myocardial infarction is a cardiovascular disease that poses a serious threat to human health. The traditional view is that adult mammalian cardiomyocytes have almost no regenerative ability, but recent studies have shown that they have regenerative potential under specific conditions. This article comprehensively describes the research progress of post-infarction cardiomyocyte regeneration, including the characteristics of cardiomyocytes and post-infarction changes, regeneration mechanisms, influencing factors, potential therapeutic strategies, challenges and future development directions, and deeply discusses the specific pathways and targets included in the regeneration mechanism, aiming to provide new ideas and methods for the treatment of myocardial infarction.

Pediatric flecainide pharmacogenomics: a roadmap to delivering precision-based care to pediatrics arrhythmias

Flecainide acetate is a Class 1c anti-arrhythmic with a potent sodium voltage gated channel blockade which is utilized for the second-line treatment of tachyarrhythmias in children and adults. Given its narrow therapeutic index, the individualization of drug therapy is of utmost importance for clinicians. Despite efforts to improve anti-arrhythmic drug therapy, there remain knowledge gaps regarding the impact of variation in the genes relevant to flecainide's disposition and response. This variability is compounded in developing children whose drug disposition and response pathways may remain immature. The purpose of this comprehensive review is to outline flecainide's disposition and response pathways while simultaneously highlighting opportunities for prospective investigation in the pediatric population.

Selective fluorescent labeling of cellular proteins and its biological applications

Proteins, which are ubiquitous in cells and critical to almost all cellular functions, are indispensable for life. Fluorescence imaging of proteins is key to understanding their functions within their native milieu, as it provides insights into protein localization, dynamics, and trafficking in living systems. Consequently, the selective labeling of target proteins with fluorophores has emerged as a highly active research area, encompassing bioorganic chemistry, chemical biology, and cell biology. Various methods for selectively labeling proteins with fluorophores in cells and tissues have been established and are continually being developed to visualize and characterize proteins. This review highlights research findings reported since 2018, with a focus on the selective labeling of cellular proteins with small organic fluorophores and their biological applications in studying protein-associated biological events. We also discuss the strengths and weaknesses of each labeling approach for their utility in living systems.

Electrophysiological Mechanism of Catestatin Antiarrhythmia: Enhancement of Ito, IK, and IK1 and Inhibition of ICa-L in Rat Ventricular Myocytes

BACKGROUND

Cardiovascular disease remains one of the leading causes of death globally. Myocardial ischemia and infarction, in particular, frequently cause disturbances in cardiac electrical activity that can trigger ventricular arrhythmias. We aimed to investigate whether catestatin, an endogenous catecholamine-inhibiting peptide, ameliorates myocardial ischemia-induced ventricular arrhythmias in rats and the underlying ionic mechanisms.

METHODS AND RESULTS

Adult male Sprague-Dawley rats were randomly divided into control and catestatin groups. Ventricular arrhythmias were induced by ligation of the left anterior descending coronary artery and electrical stimulation. Action potential, transient outward potassium current, delayed rectifier potassium current, inward rectifying potassium current, and L-type calcium current (ICa-L) of rat ventricular myocytes were recorded using a patch-clamp technique. Catestatin notably reduced ventricular arrhythmia caused by myocardial ischemia/reperfusion and electrical stimulation of rats. In ventricular myocytes, catestatin markedly shortened the action potential duration of ventricular myocytes, which was counteracted by potassium channel antagonists TEACl and 4-AP, and ICa-L current channel agonist Bay K8644. In addition, catestatin significantly increased transient outward potassium current, delayed rectifier potassium current, and inward rectifying potassium current density in a concentration-dependent manner. Catestatin accelerated the activation and decelerated the inactivation of the transient outward potassium current channel. Furthermore, catestatin decreased ICa-L current density in a concentration-dependent manner. Catestatin also accelerated the inactivation of the ICa-L channel and slowed down the recovery of ICa-L from inactivation.

CONCLUSIONS

Catestatin enhances the activity of transient outward potassium current, delayed rectifier potassium current, and inward rectifying potassium current, while suppressing the ICa-L in ventricular myocytes, leading to shortened action potential duration and ultimately reducing the ventricular arrhythmia in rats.

Paradoxical SERCA dysregulation contributes to atrial fibrillation in a model of diet-induced obesity

Obesity is a major risk factor for atrial fibrillation (AF) the most common serious cardiac arrhythmia, but the molecular mechanisms underlying diet-induced AF remain unclear. In this study, we subjected mice to a chronic high-fat diet and acute sympathetic activation ('two-hit' model) to study the mechanisms by which diet-induced obesity promotes AF. Surface electrocardiography revealed that diet-induced obesity and sympathetic activation synergize during intracardiac tachypacing to induce AF. At the cellular level, diet-induced obesity and acute adrenergic stimulation facilitate the formation of delayed afterdepolarizations in atrial myocytes, implicating altered Ca2+ dynamics as the underlying cause of AF. We found that diet-induced obesity does not alter the expression of major Ca2+-handling proteins in atria, including the sarcoplasmic reticulum Ca2+-ATPase (SERCA), a major component of beat-to-beat Ca2+ cycling in the heart. Paradoxically, obesity reduces phospholamban phosphorylation, suggesting decreased SERCA activity, yet atrial myocytes from obese mice showed a significantly increased Ca2+ transient amplitude and SERCA-mediated Ca2+ uptake. Adrenergic stimulation further increases the Ca2+ transient amplitude but does not affect Ca2+ reuptake in atrial myocytes from obese mice. Transcriptomics analysis showed that a high-fat diet prompts upregulation of neuronatin, a protein that has been implicated in obesity and is known to stimulate SERCA activity. We propose a mechanism in which obesity primes SERCA for paradoxical activation, and adrenergic stimulation facilitates AF conversion through a Ca2+-induced Ca2+ release gain in atrial myocytes. Overall, this study links obesity, altered Ca2+ signaling, and AF, and targeting this mechanism may prove effective for treating obesity-induced AF.

Management of Long QT Syndrome: A Systematic Review

Long QT syndrome (LQTS) is a cardiac disorder characterized by prolonged repolarization of the heart's electrical cycle, which can be observed as an extended QT interval on an electrocardiogram (ECG). The safe and effective management of LQTS often necessitates a multifaceted approach encompassing pharmacological treatment, lifestyle modifications, and, in high-risk cases, the implantation of implantable cardioverter-defibrillators (ICDs). Beta-blockers, particularly nadolol and propranolol, are foundational in treating LQTS, especially for high-risk patients, though ICDs are recommended for those with a history of cardiac arrest or recurrent arrhythmic episodes. Intermediate and low-risk patients are usually managed with medical therapy and regular monitoring. Lifestyle modifications, such as avoiding strenuous physical activities and certain medications, play a critical role. Additionally, psychological support is essential due to the anxiety and depression associated with LQTS. Left cardiac sympathetic denervation (LCSD) offers an alternative for those intolerant to beta-blockers or ICDs. For diagnosis and management, advancements in artificial intelligence (AI) are proving beneficial, enhancing early detection and risk stratification. Despite these developments, significant gaps in understanding the pathophysiology and optimal management strategies for LQTS remain. Future research should focus on refining risk stratification, developing new therapeutic approaches, and generating robust data to guide treatment decisions, ultimately aiming for a personalized medicine approach.

Effects of Acute and Chronic Gabapentin Treatment on Cardiovascular Function of Rats

Gabapentin (GBP), a GABA analogue, is primarily used as an anticonvulsant for the treatment of partial seizures and neuropathic pain. Whereas a majority of the side effects are associated with the nervous system, emerging evidence suggests there is a high risk of heart diseases in patients taking GBP. In the present study, we first used a preclinical model of rats to investigate, firstly, the acute cardiovascular responses to GBP (bolus i.v. injection, 50 mg/kg) and secondly the effects of chronic GBP treatment (i.p. 100 mg/kg/day × 7 days) on cardiovascular function and the myocardial proteome. Under isoflurane anesthesia, rat blood pressure (BP), heart rate (HR), and left ventricular (LV) hemodynamics were measured using Millar pressure transducers. The LV myocardium and brain cortex were analyzed by proteomics, bioinformatics, and western blot to explore the molecular mechanisms underlying GBP-induced cardiac dysfunction. In the first experiment, we found that i.v. GBP significantly decreased BP, HR, maximal LV pressure, and maximal and minimal dP/dt, whereas it increased IRP-AdP/dt, Tau, systolic, diastolic, and cycle durations (* p < 0.05 and ** p < 0.01 vs. baseline; n = 4). In the second experiment, we found that chronic GBP treatment resulted in hypotension, bradycardia, and LV systolic dysfunction, with no change in plasma norepinephrine. In the myocardium, we identified 109 differentially expressed proteins involved in calcium pathways, cholesterol metabolism, and galactose metabolism. Notably, we found that calmodulin, a key protein of intracellular calcium signaling, was significantly upregulated by GBP in the heart but not in the brain. In summary, we found that acute and chronic GBP treatments suppressed cardiovascular function in rats, which is attributed to abnormal calcium signaling in cardiomyocytes. These data reveal a novel side effect of GBP independent of the nervous system, providing important translational evidence to suggest that GBP can evoke adverse cardiovascular events by depression of myocardial function.

Unravelling Novel SCN5A Mutations Linked to Brugada Syndrome: Functional, Structural, and Genetic Insights

Brugada Syndrome (BrS) is a rare inherited cardiac arrhythmia causing potentially fatal ventricular tachycardia or fibrillation, mainly occurring during rest or sleep in young individuals without heart structural issues. It increases the risk of sudden cardiac death, and its characteristic feature is an abnormal ST segment elevation on the ECG. While BrS has diverse genetic origins, a subset of cases can be conducted to mutations in the SCN5A gene, which encodes for the Nav1.5 sodium channel. Our study focused on three novel SCN5A mutations (p.A344S, p.N347K, and p.D349N) found in unrelated BrS families. Using patch clamp experiments, we found that these mutations disrupted sodium currents: p.A344S reduced current density, while p.N347K and p.D349N completely abolished it, leading to altered voltage dependence and inactivation kinetics when co-expressed with normal channels. We also explored the effects of mexiletine treatment, which can modulate ion channel function. Interestingly, the p.N347K and p.D349N mutations responded well to the treatment, rescuing the current density, while p.A344S showed a limited response. Structural analysis revealed these mutations were positioned in key regions of the channel, impacting its stability and function. This research deepens our understanding of BrS by uncovering the complex relationship between genetic mutations, ion channel behavior, and potential therapeutic interventions.

Proarrhythmic toxicity of low dose bisphenol A and its analogs in human iPSC-derived cardiomyocytes and human cardiac organoids through delay of cardiac repolarization

Bisphenol A (BPA) and its analogs are common environmental chemicals with many potential adverse health effects. The impact of environmentally relevant low dose BPA on human heart, including cardiac electrical properties, is not understood. Perturbation of cardiac electrical properties is a key arrhythmogenic mechanism. In particular, delay of cardiac repolarization can cause ectopic excitation of cardiomyocytes and malignant arrhythmia. This can occur as a result of genetic mutations (i.e., long QT (LQT) syndrome), or cardiotoxicity of drugs and environmental chemicals. To define the impact of low dose BPA on electrical properties of cardiomyocytes in a human-relevant model system, we examined the rapid effects of 1 nM BPA in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) using patch-clamp and confocal fluorescence imaging. Acute exposure to BPA delayed repolarization and prolonged action potential duration (APD) in hiPSC-CMs through inhibition of the hERG K+ channel. In nodal-like hiPSC-CMs, BPA acutely increased pacing rate through stimulation of the If pacemaker channel. Existing arrhythmia susceptibility determines the response of hiPSC-CMs to BPA. BPA resulted in modest APD prolongation but no ectopic excitation in baseline condition, while rapidly promoted aberrant excitations and tachycardia-like events in myocytes that had drug-simulated LQT phenotype. In hiPSC-CM-based human cardiac organoids, the effects of BPA on APD and aberrant excitation were shared by its analog chemicals, which are often used in "BPA-free" products, with bisphenol AF having the largest effects. Our results reveal that BPA and its analogs have repolarization delay-associated pro-arrhythmic toxicity in human cardiomyocytes, particularly in myocytes that are prone to arrhythmias. The toxicity of these chemicals depends on existing pathophysiological conditions of the heart, and may be particularly pronounced in susceptible individuals. An individualized approach is needed in risk assessment and protection.

[Asymptomatic channelopathies : Risk stratification and primary prophylaxis]

In general, asymptomatic patients with channelopathies are at increased risk of sudden cardiac death (SCD), due to pathogenic variants in genes encoding ion channels that result in pathological ion currents. Channelopathies include long-QT syndrome (LQTS), Brugada syndrome (BrS), catecholaminergic polymorphic ventricular tachycardia (CPVT), and short-QT syndrome (SQTS). In addition to the patient's clinical presentation, history and clinical tests, the main diagnostic tools are electrocardiography and genetic testing to identify known gene mutations. Early and correct diagnosis as well as further risk stratification of affected individuals and their relatives are paramount for prognosis. The recent availability of risk score calculators for LQTS and BrS allows SCD risk to be accurately estimated. The extent to which these improve patient selection for treatment with an implantable cardioverter-defibrillator (ICD) system is currently unknown. In most cases, initiation of basic therapy in asymptomatic patients in the form of avoidance of triggers, which are usually medication or stressful situations, is sufficient and contributes to risk reduction. In addition, there are other risk-reducing prophylactic measures, such as permanent medication with nonselective β‑ blockers (for LQTS and CPVT) or mexiletine for LQTS3. Patients and their family members should be referred to specialized outpatient clinics for individual risk stratification in the sense of primary prophylaxis.

The retinal pigment epithelium displays electrical excitability and lateral signal spreading

BACKGROUND

The non-neuronal retinal pigment epithelium (RPE) functions in intimate association with retinal photoreceptors, performing a multitude of tasks critical for maintaining retinal homeostasis and collaborating with retinal glial cells to provide metabolic support and ionic buffering. Accordingly, the RPE has recently been shown to display dynamic properties mediated by an array of ion channels usually more characteristic of astrocytes and excitable cells. The recent discovery of canonical voltage-activated Na⁺ channels in the RPE and their importance for phagocytosis of photoreceptor outer segments raises a question about their electrogenic function. Here, we performed a detailed electrophysiological analysis related to the functioning of these channels in human embryonic stem cell (hESC)-derived RPE.

RESULTS

Our studies examining the electrical properties of the hESC-RPE revealed that its membrane mainly displays passive properties in a broad voltage range, with the exception of depolarization-induced spikes caused by voltage-activated Na⁺ current (I_Na). Spike amplitude depended on the availability of I_Na and spike kinetics on the membrane time constant, and the spikes could be largely suppressed by TTX. Membrane resistance fluctuated rapidly and strongly, repeatedly changing over the course of recordings and causing closely correlated fluctuations in resting membrane potential. In a minority of cells, we found delayed secondary I_Na-like inward currents characterized by comparatively small amplitudes and slow kinetics, which produced secondary depolarizing spikes. Up to three consecutive delayed inward current waves were detected. These currents could be rapidly and reversibly augmented by applying L-type Ca²⁺ channel blocker nifedipine to diminish influx of calcium and thus increase gap junctional conductance.

CONCLUSIONS

This work shows, for the first time, that I_Na and I_Na-mediated voltage spikes can spread laterally through gap junctions in the monolayer of cells that are traditionally considered non-excitable. Our findings support a potential role of the RPE that goes beyond giving homeostatic support to the retina.

Chinese herbal medicine for the treatment of cardiovascular diseases ─ targeting cardiac ion channels

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality, imposing an increasing global health burden. Cardiac ion channels (voltage-gated Na_V, Ca_V, K_Vs, and others) synergistically shape the cardiac action potential (AP) and control the heartbeat. Dysfunction of these channels, due to genetic mutations, transcriptional or post-translational modifications, may disturb the AP and lead to arrhythmia, a major risk for CVD patients. Although there are five classes of anti-arrhythmic drugs available, they can have varying levels of efficacies and side effects on patients, possibly due to the complex pathogenesis of arrhythmias. As an alternative treatment option, Chinese herbal remedies have shown promise in regulating cardiac ion channels and providing anti-arrhythmic effects. In this review, we first discuss the role of cardiac ion channels in maintaining normal heart function and the pathogenesis of CVD, then summarize the classification of Chinese herbal compounds, and elaborate detailed mechanisms of their efficacy in regulating cardiac ion channels and in alleviating arrhythmia and CVD. We also address current limitations and opportunities for developing new anti-CVD drugs based on Chinese herbal medicines.

The physics of heart rhythm disorders

The global burden caused by cardiovascular disease is substantial, with heart disease representing the most common cause of death around the world. There remains a need to develop better mechanistic models of cardiac function in order to combat this health concern. Heart rhythm disorders, or arrhythmias, are one particular type of disease which has been amenable to quantitative investigation. Here we review the application of quantitative methodologies to explore dynamical questions pertaining to arrhythmias. We begin by describing single-cell models of cardiac myocytes, from which two and three dimensional models can be constructed. Special focus is placed on results relating to pattern formation across these spatially-distributed systems, especially the formation of spiral waves of activation. Next, we discuss mechanisms which can lead to the initiation of arrhythmias, focusing on the dynamical state of spatially discordant alternans, and outline proposed mechanisms perpetuating arrhythmias such as fibrillation. We then review experimental and clinical results related to the spatio-temporal mapping of heart rhythm disorders. Finally, we describe treatment options for heart rhythm disorders and demonstrate how statistical physics tools can provide insights into the dynamics of heart rhythm disorders.

Research Progress on Natural Products’ Therapeutic Effects on Atrial Fibrillation by Regulating Ion Channels

Antiarrhythmic drugs (AADs) have a therapeutic effect on atrial fibrillation (AF) by regulating the function of ion channels. However, several adverse effects and high recurrence rates after drug withdrawal seriously affect patients’ medication compliance and clinical prognosis. Thus, safer and more effective drugs are urgently needed. Active components extracted from natural products are potential choices for AF therapy. Natural products like Panax notoginseng (Burk.) F.H. Chen, Sophora flavescens Ait., Stephania tetrandra S. Moore., Pueraria lobata (Willd.) Ohwi var. thomsonii (Benth.) Vaniot der Maesen., and Coptis chinensis Franch. have a long history in the treatment of arrhythmia, myocardial infarction, stroke, and heart failure in China. Based on the classification of chemical structures, this article discussed the natural product components’ therapeutic effects on atrial fibrillation by regulating ion channels, connexins, and expression of related genes, in order to provide a reference for development of therapeutic drugs for atrial fibrillation.

Long QT syndrome - Bench to bedside

Long QT syndrome (LQTS) is a cardiovascular disorder characterized by an abnormality in cardiac repolarization leading to a prolonged QT interval and T-wave irregularities on the surface electrocardiogram. It is commonly associated with syncope, seizures, susceptibility to torsades de pointes, and risk for sudden death. LQTS is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. The availability of therapy for this lethal disease emphasizes the importance of early and accurate diagnosis. Additionally, understanding of the molecular mechanisms underlying LQTS could help to optimize genotype-specific treatments to prevent deaths in LQTS patients. In this review, we briefly summarize current knowledge regarding molecular underpinning of LQTS, in particular focusing on LQT1, LQT2, and LQT3, and discuss novel strategies to study ion channel dysfunction and drug-specific therapies in LQT1, LQT2, and LQT3 syndromes.

Diabetes-induced changes in cardiac voltage-gated ion channels

Diabetes mellitus affects the heart through various mechanisms such as microvascular defects, metabolic abnormalities, autonomic dysfunction and incompatible immune response. Furthermore, it can also cause functional and structural changes in the myocardium by a disease known as diabetic cardiomyopathy (DCM) in the absence of coronary artery disease. As DCM progresses it causes electrical remodeling of the heart, left ventricular dysfunction and heart failure. Electrophysiological changes in the diabetic heart contribute significantly to the incidence of arrhythmias and sudden cardiac death in diabetes mellitus patients. In recent studies, significant changes in repolarizing K+ currents, Na+ currents and L-type Ca2+ currents along with impaired Ca2+ homeostasis and defective contractile function have been identified in the diabetic heart. In addition, insulin levels and other trophic factors change significantly to maintain the ionic channel expression in diabetic patients. There are many diagnostic tools and management options for DCM, but it is difficult to detect its development and to effectively prevent its progress. In this review, diabetes-associated alterations in voltage-sensitive cardiac ion channels are comprehensively assessed to understand their potential role in the pathophysiology and pathogenesis of DCM.

Yulink, predicted from evolutionary analysis, is involved in cardiac function

Background

The comparative evolutionary genomics analysis was used to study the functions of novel Ka/Ks-predicted human exons in a zebrafish model. The Yulink (MIOS, Entrez Gene: 54,468), a conserved gene from zebrafish to human with WD40 repeats at N-terminus, was identified and found to encode an 875 amino acid in human. The biological function of this Yulink gene in cardiomyocytes remains unexplored. The purpose of this study is to determine the involvement of Yulink in the functions of cardiomyocytes and to investigate its molecular regulatory mechanism.

Methods

Knockdown of Yulink was performed using morpholino or shRNA in zebrafish, mouse HL-1 cardiomyocytes, and human iPSC-derived cardiomyocytes. The expression levels of mRNA and protein were quantified by qPCR and western blots. Other methods including DNA binding, ligand uptake, agonists treatment and Ca²⁺ imaging assays were used to study the molecular regulatory mechanism by Yulink. Statistical data were shown as mean ± SD or mean ± standard error.

Results

The knockdown of yulink with three specific morpholinos in zebrafish resulted in cardiac dysfunctions with pericardial edema, decreased heart beats and cardiac output. The Yulink knockdown in mouse HL-1 cardiomyocytes disrupted Ca²⁺ cycling, reduced DNA binding activity of PPARγ (peroxisome proliferator-activated receptor gamma) and resulted in a reduction of Serca2 (sarcoplasmic reticulum Ca²⁺ ATPase 2) expression. Expression of Serca2 was up-regulated by PPARγ agonists and down-regulated by PPARγ-shRNA knockdown, suggesting that Yulink regulates SERCA2 expression through PPARγ in mouse HL-1 cardiomyocytes. On the other hand, YULINK, PPARγ or SERCA2 over-expression rescued the phenotypes of Yulink KD cells. In addition, knockdown of YULINK in human iPSC-derived cardiomyocytes also disrupted Ca²⁺ cycling via decreased SERCA2 expression.

Conclusions

Overall, our data showed that Yulink is an evolutionarily conserved gene from zebrafish to human. Mechanistically Yulink regulated Serca2 expression in cardiomyocytes, presumably mediated through PPARγ nuclear entry. Deficiency of Yulink in mouse and human cardiomyocytes resulted in irregular Ca²⁺ cycling, which may contribute to arrhythmogenesis.

Established and Emerging Mechanisms in the Pathogenesis of Arrhythmogenic Cardiomyopathy: A Multifaceted Disease

Arrhythmogenic cardiomyopathy (ACM) is a heritable myocardial disease that manifests with cardiac arrhythmias, syncope, sudden cardiac death, and heart failure in the advanced stages. The pathological hallmark of ACM is a gradual replacement of the myocardium by fibroadiposis, which typically starts from the epicardium. Molecular genetic studies have identified causal mutations predominantly in genes encoding for desmosomal proteins; however, non-desmosomal causal mutations have also been described, including genes coding for nuclear proteins, cytoskeleton componentsand proteins involved in excitation-contraction coupling. Despite the poor prognosis, currently available treatments can only partially control symptoms and to date there is no effective therapy for ACM. Inhibition of the canonical Wnt/β-catenin pathway and activation of the Hippo and the TGF-β pathways have been implicated in the pathogenesis of ACM. Yet, our understanding of the molecular mechanisms involved in the development of the disease and the cell source of fibroadiposis remains incomplete. Elucidation of the pathogenesis of the disease could facilitate targeted approaches for treatment. In this manuscript we will provide a comprehensive review of the proposed molecular and cellular mechanisms of the pathogenesis of ACM, including the emerging evidence on abnormal calcium homeostasis and inflammatory/autoimmune response. Moreover, we will propose novel hypothesis about the role of epicardial cells and paracrine factors in the development of the phenotype. Finally, we will discuss potential innovative therapeutic approaches based on the growing knowledge in the field.

Atrial Fibrillation in COVID-19: From Epidemiological Association to Pharmacological Implications

Coronavirus disease 2019 (COVID-19) outbreak is a public health emergency of international concerns because of a highly pathogenic human coronavirus (HCoV), actually named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Despite much emerging data about the epidemiological association between cardiovascular diseases and COVID-19, little is still known about atrial fibrillation and its optimal management in this clinical contest. The aim of our review is to describe the pharmacological interactions between cardiovascular drugs more commonly used in atrial fibrillation management and experimental COVID-19 therapies, based on EU and US summaries of product characteristics.

Calibration of ionic and cellular cardiac electrophysiology models

Cardiac electrophysiology models are among the most mature and well-studied mathematical models of biological systems. This maturity is bringing new challenges as models are being used increasingly to make quantitative rather than qualitative predictions. As such, calibrating the parameters within ion current and action potential (AP) models to experimental data sets is a crucial step in constructing a predictive model. This review highlights some of the fundamental concepts in cardiac model calibration and is intended to be readily understood by computational and mathematical modelers working in other fields of biology. We discuss the classic and latest approaches to calibration in the electrophysiology field, at both the ion channel and cellular AP scales. We end with a discussion of the many challenges that work to date has raised and the need for reproducible descriptions of the calibration process to enable models to be recalibrated to new data sets and built upon for new studies. This article is categorized under: Analytical and Computational Methods > Computational Methods Physiology > Mammalian Physiology in Health and Disease Models of Systems Properties and Processes > Cellular Models.

Opening large-conductance potassium channels selectively induced cell death of triple-negative breast cancer

Background

Unlike other breast cancer subtypes that may be treated with a variety of hormonal or targeted therapies, there is a need to identify new, effective targets for triple-negative breast cancer (TNBC). It has recently been recognized that membrane potential is depolarized in breast cancer cells. The primary objective of the study is to explore whether hyperpolarization induced by opening potassium channels may provide a new strategy for treatment of TNBC.

Methods

Breast cancer datasets in cBioPortal for cancer genomics was used to search for ion channel gene expression. Immunoblots and immunohistochemistry were used for protein expression in culture cells and in the patient tissues. Electrophysiological patch clamp techniques were used to study properties of BK channels in culture cells. Flow cytometry and fluorescence microscope were used for cell viability and cell cycle studies. Ultrasound imaging was used to study xenograft in female NSG mice.

Results

In large datasets of breast cancer patients, we identified a gene, KCNMA1 (encoding for a voltage- and calcium-dependent large-conductance potassium channel, called BK channel), overexpressed in triple-negative breast cancer patients. Although overexpressed, 99% of channels are closed in TNBC cells. Opening BK channels hyperpolarized membrane potential, which induced cell cycle arrest in G2 phase and apoptosis via caspase-3 activation. In a TNBC cell induced xenograft model, treatment with a BK channel opener significantly slowed tumor growth without cardiac toxicity.

Conclusions

Our results support the idea that hyperpolarization induced by opening BK channel in TNBC cells can become a new strategy for development of a targeted therapy in TNBC.

Cannabidiol protects against high glucose-induced oxidative stress and cytotoxicity in cardiac voltage-gated sodium channels

BACKGROUND AND PURPOSE

Cardiovascular complications are the major cause of mortality in diabetic patients. However, the molecular mechanisms underlying diabetes-associated arrhythmias are unclear. We hypothesized that high glucose could adversely affect Na_v 1.5, the major cardiac sodium channel isoform of the heart, at least partially via oxidative stress. We further hypothesized that cannabidiol (CBD), one of the main constituents of Cannabis sativa, through its effects on Na_v 1.5, could protect against high glucose-elicited oxidative stress and cytotoxicity.

EXPERIMENTAL APPROACH

To test these ideas, we used CHO cells transiently co-transfected with cDNA encoding human Na_v 1.5 α-subunit under control and high glucose conditions (50 or 100 mM for 24 hr). Several experimental and computational techniques were used, including voltage clamp of heterologous expression systems, cell viability assays, fluorescence assays and action potential modelling.

KEY RESULTS

High glucose evoked cell death associated with elevation in reactive oxygen species (ROS) right shifted the voltage dependence of conductance and steady-state fast inactivation, and increased persistent current leading to computational prolongation of action potential (hyperexcitability) which could result in long QT3 arrhythmia. CBD mitigated all the deleterious effects provoked by high glucose. Perfusion with lidocaine (a well-known sodium channel inhibitor with antioxidant effects) or co-incubation of Tempol (a well-known antioxidant) elicited protection, comparable to CBD, against the deleterious effects of high glucose.

CONCLUSION AND IMPLICATIONS

These findings suggest that, through its favourable antioxidant and sodium channel inhibitory effects, CBD may protect against high glucose-induced arrhythmia and cytotoxicity.

Newly Discovered Action of HpTx3 from Venom of Heteropoda venatoria on Nav1.7 and Its Pharmacological Implications in Analgesia

It has been reported that Heteropodatoxin3 (HpTx3), a peptidic neurotoxin purified from the venom of the spider species Heteropoda venatoria, could inhibit K_v4.2 channels. Our present study newly found that HpTx3 also has potent and selective inhibitory action on Na_v1.7, with an IC₅₀ of 135.61 ± 12.98 nM. Without effect on the current–voltage (I-V) relationship of Na_v1.7, HpTx3 made minor alternation in the voltage-dependence of activation and steady-state inactivation of Na_v1.7 (4.15 mV and 7.29 mV, respectively) by interacting with the extracellular S3–S4 loop (S3b–S4 sequence) in domain II and the domain IV of the Na_v channel subtype, showing the characteristics of both pore blocker and gate modifier toxin. During the interaction of HpTx3 with the S3b–S4 sequence of Na_v1.7, the amino acid residue D in the sequence played a key role. When administered intraperitoneally or intramuscularly, HpTx3 displayed potent analgesic activity in a dose-dependent manner in different mouse pain models induced by formalin, acetic acid, complete Freund’s adjuvant, hot plate, or spared nerve injury, demonstrating that acute, inflammatory, and neuropathic pains were all effectively inhibited by the toxin. In most cases HpTx3 at doses of ≥ 1mg/kg could produce the analgesic effect comparable to that of 1 mg/kg morphine. These results suggest that HpTx3 not only can be used as a molecular probe to investigate ion channel function and pain mechanism, but also has potential in the development of the drugs that treat the Na_v1.7 channel-related pain.

Histone deacetylase inhibition by Entinostat for the prevention of electrical and structural remodeling in heart failure

Background

The development of heart failure is accompanied by complex changes in cardiac electrophysiology and functional properties of cardiomyocytes and fibroblasts. Histone deacetylase (HDAC) inhibitors hold great promise for the pharmaceutical therapy of several malignant diseases. Here, we describe novel effects of the class I HDAC inhibitor Entinostat on electrical and structural remodeling in an in vivo model of pacing induced heart failure.

Methods

Rabbits were implanted a pacemaker system, subjected to rapid ventricular pacing and treated with Entinostat or placebo, respectively. Following stimulation, rabbit hearts were explanted and subsequently subjected to electrophysiological studies and further immunohistological analyses of left ventricles.

Results

In vivo, rapid ventricular stimulation caused a significant prolongation of monophasic action potential duration compared to sham hearts (from 173 ± 26 ms to 250 ± 41 ms; cycle length 900 ms; p < 0.05) and an increased incidence of Early afterdepolarisations (+ 150%), while treatment with Entinostat in failing hearts could partially prevent this effect (from 250 ± 41 ms to 170 ± 53 ms, p < 0.05; reduction in EAD by 50%). Entinostat treatment partially restored KCNH2 and Cav1.3 gene expressions in failing hearts, and inhibited the development of cardiac fibrosis in vivo.

Conclusion

In a rabbit model of heart failure, Entinostat diminishes heart failure related prolongation of repolarization and partially restores KCNH2 and Cav1.3 expression. In addition, Entinostat exerts antifibrotic properties both in vitro and in vivo. Thus, Entinostat might be an interesting candidate for the pharmaceutical therapy of heart failure directed against structural and electrical remodeling.

Electronic supplementary material

The online version of this article (10.1186/s40360-019-0294-x) contains supplementary material, which is available to authorized users.

Channelopathy as a SUDEP Biomarker in Dravet Syndrome Patient-Derived Cardiac Myocytes

Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy with a high incidence of sudden unexpected death in epilepsy (SUDEP). Most DS patients carry de novo variants in SCN1A, resulting in Nav1.1 haploinsufficiency. Because SCN1A is expressed in heart and in brain, we proposed that cardiac arrhythmia contributes to SUDEP in DS. We generated DS patient and control induced pluripotent stem cell-derived cardiac myocytes (iPSC-CMs). We observed increased sodium current (INa) and spontaneous contraction rates in DS patient iPSC-CMs versus controls. For the subject with the largest increase in INa, cardiac abnormalities were revealed upon clinical evaluation. Generation of a CRISPR gene-edited heterozygous SCN1A deletion in control iPSCs increased INa density in iPSC-CMs similar to that seen in patient cells. Thus, the high risk of SUDEP in DS may result from a predisposition to cardiac arrhythmias in addition to seizures, reflecting expression of SCN1A in heart and brain.

Investigating the state dependence of drug binding in hERG channels using a trapped-open channel phenotype

The hERG channel is a key player in repolarization of the cardiac action potential. Pharmacological blockade of hERG channels depletes the cardiac repolarization reserve, increasing the risk of cardiac arrhythmias. The promiscuous nature of drug interactions with hERG presents a therapeutic challenge for drug design and development. Despite considerable effort, the mechanisms of drug binding remain incompletely understood. One proposed mechanism is that high-affinity drug binding preferentially occurs when channels are in the inactivated state. However, this has been difficult to test, since inactivation is rapid in hERG and access to the drug binding site is limited by slower opening of the activation gate. Here, we have directly assessed the role of inactivation in cisparide and terfenadine drug binding in mutant (I663P) hERG channels where the activation gate is trapped-open. We firstly demonstrate the utility of this approach by showing that inactivation, ion selectivity and high affinity drug binding are preserved in I663P mutant channels. We then assess the role of inactivation by applying cisapride and terfenadine at different membrane voltages, which induce varying degrees of inactivation. We show that the extent of block does not correlate with the extent of inactivation. These data suggest that inactivation is not a major determinant of cisapride or terfenadine binding in hERG channels.

Gaseous Signaling Molecules in Cardiovascular Function: From Mechanisms to Clinical Translation

Carbon monoxide (CO), hydrogen sulfide (H₂S), and nitric oxide (NO) constitute endogenous gaseous molecules produced by specific enzymes. These gases are chemically simple, but exert multiple effects and act through shared molecular targets to control both physiology and pathophysiology in the cardiovascular system (CVS). The gases act via direct and/or indirect interactions with each other in proteins such as heme-containing enzymes, the mitochondrial respiratory complex, and ion channels, among others. Studies of the major impacts of CO, H₂S, and NO on the CVS have revealed their involvement in controlling blood pressure and in reducing cardiac reperfusion injuries, although their functional roles are not limited to these conditions. In this review, the basic aspects of CO, H₂S, and NO, including their production and effects on enzymes, mitochondrial respiration and biogenesis, and ion channels are briefly addressed to provide insight into their biology with respect to the CVS. Finally, potential therapeutic applications of CO, H₂S, and NO with the CVS are addressed, based on the use of exogenous donors and different types of delivery systems.

Effects of norquetiapine, the active metabolite of quetiapine, on cloned hERG potassium channels

Quetiapine is an atypical antipsychotic drug that is widely used for the treatment of schizophrenia. It is mainly metabolized by a cytochrome P450 system in the liver. Norquetiapine is a major active metabolite in humans with a pharmacological profile that differs distinctly from that of quetiapine. We used the whole-cell patch-clamp technique to investigate the effects of norquetiapine on hERG channels that are stably expressed in HEK cells. Quetiapine and norquetiapine inhibited the hERG tail currents at -50mV in a concentration-dependent manner with IC₅₀ values of 8.3 and 10.8μM, respectively, which suggested equal potency. The block of hERG currents by norquetiapine was voltage-dependent with a steep increase over a range of voltages for channel activation. However, at more depolarized potentials where the channels were fully activated, the block by norquetiapine was voltage-independent. The steady-state inactivation curve of the hERG currents was shifted to the hyperpolarizing direction in the presence of norquetiapine. Norquetiapine did not produce a use-dependent block. A fast application of norquetiapine inhibited the hERG current elicited by a 5s depolarizing pulse to +60mV, which fully inactivated the hERG currents, suggesting an inactivated-state block. During a repolarizing pulse wherein the hERG current was slowly deactivated, albeit remaining in an open state, a fast application of norquetiapine rapidly and reversibly inhibited the open state of the hERG current. Our results indicated that quetiapine and norquetiapine had equal potency in inhibiting hERG tail currents. Norquetiapine inhibited the hERG current by preferentially interacting with the open and/or inactivated states of the channels.

Modeling the human Nav1.5 sodium channel: structural and mechanistic insights of ion permeation and drug blockade

Abnormalities in the human Nav1.5 (hNav1.5) voltage-gated sodium ion channel (VGSC) are associated with a wide range of cardiac problems and diseases in humans. Current structural models of hNav1.5 are still far from complete and, consequently, their ability to study atomistic interactions of this channel is very limited. Here, we report a comprehensive atomistic model of the hNav1.5 ion channel, constructed using homology modeling technique and refined through long molecular dynamics simulations (680 ns) in the lipid membrane bilayer. Our model was comprehensively validated by using reported mutagenesis data, comparisons with previous models, and binding to a panel of known hNav1.5 blockers. The relatively long classical MD simulation was sufficient to observe a natural sodium permeation event across the channel's selectivity filters to reach the channel's central cavity, together with the identification of a unique role of the lysine residue. Electrostatic potential calculations revealed the existence of two potential binding sites for the sodium ion at the outer selectivity filters. To obtain further mechanistic insight into the permeation event from the central cavity to the intracellular region of the channel, we further employed "state-of-the-art" steered molecular dynamics (SMD) simulations. Our SMD simulations revealed two different pathways through which a sodium ion can be expelled from the channel. Further, the SMD simulations identified the key residues that are likely to control these processes. Finally, we discuss the potential binding modes of a panel of known hNav1.5 blockers to our structural model of hNav1.5. We believe that the data presented here will enhance our understanding of the structure-property relationships of the hNav1.5 ion channel and the underlying molecular mechanisms in sodium ion permeation and drug interactions. The results presented here could be useful for designing safer drugs that do not block the hNav1.5 channel.

Distinct physiological effects of β1- and β2-adrenoceptors in mouse ventricular myocytes: insights from a compartmentalized mathematical model

The β1- and β2-adrenergic signaling systems play different roles in the functioning of cardiac cells. Experimental data show that the activation of the β1-adrenergic signaling system produces significant inotropic, lusitropic, and chronotropic effects in the heart, whereas the effects of the β2-adrenergic signaling system is less apparent. In this paper, a comprehensive compartmentalized experimentally based mathematical model of the combined β1- and β2-adrenergic signaling systems in mouse ventricular myocytes is developed to simulate the experimental findings and make testable predictions of the behavior of the cardiac cells under different physiological conditions. Simulations describe the dynamics of major signaling molecules in different subcellular compartments; kinetics and magnitudes of phosphorylation of ion channels, transporters, and Ca2+ handling proteins; modifications of action potential shape and duration; and [Ca2+]i and [Na+]i dynamics upon stimulation of β1- and β2-adrenergic receptors (β1- and β2-ARs). The model reveals physiological conditions when β2-ARs do not produce significant physiological effects and when their effects can be measured experimentally. Simulations demonstrated that stimulation of β2-ARs with isoproterenol caused a marked increase in the magnitude of the L-type Ca2+ current, [Ca2+]i transient, and phosphorylation of phospholamban only upon additional application of pertussis toxin or inhibition of phosphodiesterases of type 3 and 4. The model also made testable predictions of the changes in magnitudes of [Ca2+]i and [Na+]i fluxes, the rate of decay of [Na+]i concentration upon both combined and separate stimulation of β1- and β2-ARs, and the contribution of phosphorylation of PKA targets to the changes in the action potential and [Ca2+]i transient.

Propagation of parametric uncertainty for the K+ channel model in mouse ventricular myocytes

Cardiac potassium (K+) channel plays an important role in cardiac electrical signaling. Mathematical models have been widely used to investigate the effects of K+ channels on cardiac functions. However, the model of K+ channel involves parametric uncertainties, which can be induced by fitting the model's parameters that best capture experimental data. Since the prediction of cardiac functions are highly parameter-dependent, it is critical to quantify the influence of parametric uncertainty on the model responses to provide the more reliable predictions. This paper presents a new method to efficiently propagate the uncertainty on the model's parameters of K+ channel to the gating variables as well as the current density. In this way, we can estimate the model predictions and their corresponding confidence intervals simultaneously. A generalized polynomial chaos (gPC) expansion approximating the parametric uncertainty is used in combination with the physical models to quantify and propagate the parametric uncertainties onto the modeled predictions of steady state activation and steady state inactivation of the K+ channel. Using Galerkin projection, the variation (i.e., confidence interval) of the gating variables resulting from the uncertainty of model parameters can then be estimated in a computationally efficient fashion. As compared with the Monte Carlo (MC) simulations, the proposed methodology shows it's advantageous in terms of computational efficiency and accuracy, thus demonstrating the potential for dealing with more complicated cardiac models.

Using Zebrafish for High-Throughput Screening of Novel Cardiovascular Drugs

Cardiovascular diseases remain a major challenge for modern drug discovery. The diseases are chronic, complex, and the result of sophisticated interactions between genetics and environment involving multiple cell types and a host of systemic factors. The clinical events are often abrupt, and the diseases may be asymptomatic until a highly morbid event. Target selection is often based on limited information, and though highly specific agents are often identified in screening, their final efficacy is often compromised by unanticipated systemic responses, a narrow therapeutic index, or substantial toxicities. Our understanding of complexity of cardiovascular disease has grown dramatically over the past 2 decades, and the range of potential disease mechanisms now includes pathways previously thought only tangentially involved in cardiac or vascular disease. Despite these insights, the majority of active cardiovascular agents derive from a remarkably small number of classes of agents and target a very limited number of pathways. These agents have often been used initially for particular indications and then discovered serendipitously to have efficacy in other cardiac disorders or in a manner unrelated to their original mechanism of action. In this review, the rationale for in vivo screening is described, and the utility of the zebrafish for this approach and for complementary work in functional genomics is discussed. Current limitations of the model in this setting and the need for careful validation in new disease areas are also described. An overview is provided of the complex mechanisms underlying most clinical cardiovascular diseases, and insight is offered into the limits of single downstream pathways as drug targets. The zebrafish is introduced as a model organism, in particular for cardiovascular biology. Potential approaches to overcoming the hurdles to drug discovery in the face of complex biology are discussed, including in vivo screening of zebrafish genetic disease models.

The control of cardiac ventricular excitability by autonomic pathways

Central to the genesis of ventricular cardiac arrhythmia are variations in determinants of excitability. These involve individual ionic channels and transporters in cardiac myocytes but also tissue factors such as variable conduction of the excitation wave, fibrosis and source-sink mismatch. It is also known that in certain diseases and particularly the channelopathies critical events occur with specific stressors. For example, in hereditary long QT syndrome due to mutations in KCNQ1 arrhythmic episodes are provoked by exercise and in particular swimming. Thus not only is the static substrate important but also how this is modified by dynamic signalling events associated with common physiological responses. In this review, we examine the regulation of ventricular excitability by signalling pathways from a cellular and tissue perspective in an effort to identify key processes, effectors and potential therapeutic approaches. We specifically focus on the autonomic nervous system and related signalling pathways.

Cardiac Channelopathies and Sudden Death: Recent Clinical and Genetic Advances

Sudden cardiac death poses a unique challenge to clinicians because it may be the only symptom of an inherited heart condition. Indeed, inherited heart diseases can cause sudden cardiac death in older and younger individuals. Two groups of familial diseases are responsible for sudden cardiac death: cardiomyopathies (mainly hypertrophic cardiomyopathy, dilated cardiomyopathy, and arrhythmogenic cardiomyopathy) and channelopathies (mainly long QT syndrome, Brugada syndrome, short QT syndrome, and catecholaminergic polymorphic ventricular tachycardia). This review focuses on cardiac channelopathies, which are characterized by lethal arrhythmias in the structurally normal heart, incomplete penetrance, and variable expressivity. Arrhythmias in these diseases result from pathogenic variants in genes encoding cardiac ion channels or associated proteins. Due to a lack of gross structural changes in the heart, channelopathies are often considered as potential causes of death in otherwise unexplained forensic autopsies. The asymptomatic nature of channelopathies is cause for concern in family members who may be carrying genetic risk factors, making the identification of these genetic factors of significant clinical importance.

The Burden of Atrial Fibrillation: Should We Abandon Antiarrhythmic Drug Therapy?

Atrial fibrillation (AF) is the most common sustained arrhythmia, exacting a substantial toll in cardiovascular morbidity and mortality. Until recently, the prevailing philosophy has been that restoration and maintenance of normal sinus rhythm, as opposed to control of ventricular response rate, was the optimal approach to treatment of AF. A series of landmark trials (AFFIRM, RACE, STAF, and PIAF) have called this strategy into question, suggesting outcomes are equivalent with both approaches. These data do not mean that rhythm control is not beneficial, but highlight the limitations of current therapies to achieve and maintain sinus rhythm. Limitations of the rhythm-control strategy may be related to our difficulty in accurately documenting symptomatic benefit from this approach, the lack of efficacy and excessive adverse-effect burden associated with currently available antiarrhythmic agents, and selection biases in the enrollment of patients in clinical trials of rhythm control versus rate control, making the trials incompletely representative of the population eligible for therapy. New pharmacologic agents under development feature increased atrial selectivity or multi-channel-blocking properties (or both). As a result, these compounds may be more effective in prolonging atrial refractoriness and may also have reduced proarrhythmic potential. It is premature to abandon the concept of rhythm control in AF until we have trials designed to include younger and highly symptomatic patients, more sensitive tools to measure symptomatic improvement, and safer, more effective antiarrhythmic agents.

The Cardiac Conduction System: Generation and Conduction of the Cardiac Impulse

In this article, the authors outline the key components behind the automated generation of the cardiac impulses and the effect these impulses have on cardiac myocytes. Also, a description of the key components of the normal cardiac conduction system is provided, including the sinoatrial node, the atrioventricular node, the His bundle, the bundle branches, and the Purkinje network. Finally, an outline of how each stage of the cardiac conduction system is represented on the electrocardiogram is described, allowing the reader of the electrocardiogram to translate background information about the normal cardiac conduction system to everyday clinical practice.

Mechanisms of Electrical Activation and Conduction in the Gastrointestinal System: Lessons from Cardiac Electrophysiology

The gastrointestinal (GI) tract is an electrically excitable organ system containing multiple cell types, which coordinate electrical activity propagating through this tract. Disruption in its normal electrophysiology is observed in a number of GI motility disorders. However, this is not well characterized and the field of GI electrophysiology is much less developed compared to the cardiac field. The aim of this article is to use the established knowledge of cardiac electrophysiology to shed light on the mechanisms of electrical activation and propagation along the GI tract, and how abnormalities in these processes lead to motility disorders and suggest better treatment options based on this improved understanding. In the first part of the article, the ionic contributions to the generation of GI slow wave and the cardiac action potential (AP) are reviewed. Propagation of these electrical signals can be described by the core conductor theory in both systems. However, specifically for the GI tract, the following unique properties are observed: changes in slow wave frequency along its length, periods of quiescence, synchronization in short distances and desynchronization over long distances. These are best described by a coupled oscillator theory. Other differences include the diminished role of gap junctions in mediating this conduction in the GI tract compared to the heart. The electrophysiology of conditions such as gastroesophageal reflux disease and gastroparesis, and functional problems such as irritable bowel syndrome are discussed in detail, with reference to ion channel abnormalities and potential therapeutic targets. A deeper understanding of the molecular basis and physiological mechanisms underlying GI motility disorders will enable the development of better diagnostic and therapeutic tools and the advancement of this field.

Shensong Yangxin capsules prevent ischemic arrhythmias by prolonging action potentials and alleviating Ca2+ overload

Shensong Yangxin capsules (SSYX) are an effective traditional Chinese medicine that has been used to treat coronary heart disease clinically. The present study aimed to establish whether SSYX prevent ischemic arrhythmias in rats, and to explore the underlying mechanisms. Male rats were pretreated with distilled water, SSYX and amiodarone for one week. Acute myocardial ischemia (AMI) was performed to induce ischemic arrhythmias. The incidence and severity of ischemic arrhythmias were evaluated. The action potential, transient outward K+ current (Ito) and inward rectifier K+ current (IK1) of rat cardiomyocytes were measured using the patch‑clamp technique. The intracellular Ca2+ concentration of the cardiomyocytes was measured using a laser scanning confocal microscope. The results revealed that SSYX lowered the incidence of arrhythmia markedly during AMI. Furthermore, SSYX delayed the appearance, and reduced the severity, of ischemic arrhythmias compared with the control. In addition, SSYX markedly decreased the ratio of the myocardial infarction region to the whole heart. In an in vitro study, SSYX prolonged the action potential duration of rat cardiomyocytes, and inhibited Ito and IK1 markedly. Additionally, SSYX inhibited Ca2+ elevation induced by KCl in cardiomyocytes. These results suggested that SSYX prevents ischemic arrhythmia, and the underlying mechanism responsible for this process may include prolonging the action potential and alleviating Ca2+ overload.

Cardioprotective effects of fatty acid amide hydrolase inhibitor URB694, in a rodent model of trait anxiety

In humans, chronic anxiety represents an independent risk factor for cardiac arrhythmias and sudden death. Here we evaluate in male Wistar rats bred for high (HAB) and low (LAB) anxiety-related behavior, as well as non-selected (NAB) animals, the relationship between trait anxiety and cardiac electrical instability and investigate whether pharmacological augmentation of endocannabinoid anandamide-mediated signaling exerts anxiolytic-like and cardioprotective effects. HAB rats displayed (i) a higher incidence of ventricular tachyarrhythmias induced by isoproterenol, and (ii) a larger spatial dispersion of ventricular refractoriness assessed by means of an epicardial mapping protocol. In HAB rats, acute pharmacological inhibition of the anandamide-degrading enzyme, fatty acid amide hydrolase (FAAH), with URB694 (0.3 mg/kg), (i) decreased anxiety-like behavior in the elevated plus maze, (ii) increased anandamide levels in the heart, (iii) reduced isoproterenol-induced occurrence of ventricular tachyarrhythmias, and (iv) corrected alterations of ventricular refractoriness. The anti-arrhythmic effect of URB694 was prevented by pharmacological blockade of the cannabinoid type 1 (CB₁), but not of the CB₂, receptor. These findings suggest that URB694 exerts anxiolytic-like and cardioprotective effects in HAB rats, the latter via anandamide-mediated activation of CB₁ receptors. Thus, pharmacological inhibition of FAAH might be a viable pharmacological strategy for the treatment of anxiety-related cardiac dysfunction.

Cardiotoxicodynamics: Toxicity of Cardiovascular Xenobiotics

Maintaining adequate tissue perfusion depends on a variety of factors, all of which can be influenced by xenobiotics (substances foreign to the body, including pharmaceuticals, chemicals, and natural compounds). Volume status, systemic vascular resistance, myocardial contractility, and cardiac rhythm all play a significant role in ensuring hemodynamic stability and proper cardiovascular function. Direct effects on the nervous system, the vasculature, or the heart itself as well as indirect metabolic effects may play a significant role in the development of cardiotoxicity. This article is dedicated to discussion of the disruption of cardiovascular physiology by xenobiotics.

[Long QT syndrome. History, genetics, clinical symptoms, causes and therapy]

The long QT syndrome is caused by a change in cardiac repolarization due to functional ion channel defects. A differentiation is made between a congenital (cLQTS) and an acquired (aLQTS) form of the disease. The disease results in the name-giving prolongation of the QT interval in the electrocardiogram and represents a predisposition for cardiac arrhythmia and sudden cardiac death. This article summarizes the current knowledge on the history, pathophysiology, clinical symptoms and therapy of cLQTS and aLQTS. This knowledge of pathophysiological features of the symptoms allows the underlying anesthesiological approach for individualized perioperative concepts for patients suffering from LQTS to be derived.

Mechanisms of sudden cardiac death: oxidants and metabolism

Ventricular arrhythmia is the leading cause of sudden cardiac death (SCD). Deranged cardiac metabolism and abnormal redox state during cardiac diseases foment arrhythmogenic substrates through direct or indirect modulation of cardiac ion channel/transporter function. This review presents current evidence on the mechanisms linking metabolic derangement and excessive oxidative stress to ion channel/transporter dysfunction that predisposes to ventricular arrhythmias and SCD. Because conventional antiarrhythmic agents aiming at ion channels have proven challenging to use, targeting arrhythmogenic metabolic changes and redox imbalance may provide novel therapeutics to treat or prevent life-threatening arrhythmias and SCD.

Protein assemblies of sodium and inward rectifier potassium channels control cardiac excitability and arrhythmogenesis

The understanding of how cardiac ion channels function in the normal and the diseased heart has greatly increased over the last four decades thanks to the advent of patch-clamp technology and, more recently, the emergence of genetics, as well as cellular and molecular cardiology. However, our knowledge of how these membrane-embedded proteins physically interact with each other within macromolecular complexes remains incomplete. This review focuses on how the main cardiac inward sodium channel (NaV1.5) and the strong inward rectifier potassium channel (Kir2.1) function within macromolecular complexes to control cardiac excitability. It has become increasingly clear that these two important ion channel proteins physically interact with multiple other protein partners and with each other from early stages of protein trafficking and targeting through membrane anchoring, recycling, and degradation. Recent findings include compartmentalized regulation of NaV1.5 channel expression and function through a PDZ (postsynaptic density protein, Drosophila disc large tumor suppressor, and zonula occludens-1 protein) domain-binding motif, and interaction of caveolin-3 with Kir2.1 and ankyrin-G as a molecular platform for NaV1.5 signaling. At the cardiomyocyte membrane, NaV1.5 and Kir2.1 interact through at least two distinct PDZ domain-scaffolding proteins (synapse-associated protein-97 and α1-syntrophin), thus modulating reciprocally their cell-surface expression at two different microdomains. Emerging evidence also shows that inheritable mutations in plakophilin-2, ankyrin-G, dystrophin, syntrophin, synapse-associated protein-97, and caveolin-3, among others, modify functional expression and/or localization in the cardiac cell of NaV1.5, Kir2.1 or both to give rise to arrhythmogenic diseases. Unveiling the mechanistic underpinnings of macromolecular interactions should increase our understanding of inherited and acquired arrhythmogenic cardiac diseases and may lead to advances in therapy.

Anesthetic drug midazolam inhibits cardiac human ether-à-go-go-related gene channels: mode of action

Midazolam is a short-acting benzodiazepine that is in wide clinical use as an anxiolytic, sedative, hypnotic, and anticonvulsant. Midazolam has been shown to inhibit ion channels, including calcium and potassium channels. So far, the effects of midazolam on cardiac human ether-à-go-go-related gene (hERG) channels have not been analyzed. The inhibitory effects of midazolam on heterologously expressed hERG channels were analyzed in Xenopus oocytes using the double-electrode voltage clamp technique. We found that midazolam inhibits hERG channels in a concentration-dependent manner, yielding an IC₅₀ of 170 μM in Xenopus oocytes. When analyzed in a HEK 293 cell line using the patch-clamp technique, the IC₅₀ was 13.6 μM. Midazolam resulted in a small negative shift of the activation curve of hERG channels. However, steady-state inactivation was not significantly affected. We further show that inhibition is state-dependent, occurring within the open and inactivated but not in the closed state. There was no frequency dependence of block. Using the hERG pore mutants F656A and Y652A we provide evidence that midazolam uses a classical binding site within the channel pore. Analyzing the subacute effects of midazolam on hERG channel trafficking, we further found that midazolam does not affect channel surface expression. Taken together, we show that the anesthetic midazolam is a low-affinity inhibitor of cardiac hERG channels without additional effects on channel surface expression. These data add to the current understanding of the pharmacological profile of the anesthetic midazolam.

Electrophysiologic substrate in congenital Long QT syndrome: noninvasive mapping with electrocardiographic imaging (ECGI)

BACKGROUND

Congenital Long QT syndrome (LQTS) is an arrhythmogenic disorder that causes syncope and sudden death. Although its genetic basis has become well-understood, the mechanisms whereby mutations translate to arrhythmia susceptibility in the in situ human heart have not been fully defined. We used noninvasive ECG imaging to map the cardiac electrophysiological substrate and examine whether LQTS patients display regional heterogeneities in repolarization, a substrate that promotes arrhythmogenesis.

METHODS AND RESULTS

Twenty-five subjects (9 LQT1, 9 LQT2, 5 LQT3, and 2 LQT5) with genotype and phenotype positive LQTS underwent ECG imaging. Seven normal subjects provided control. Epicardial maps of activation, recovery times, activation-recovery intervals, and repolarization dispersion were constructed. Activation was normal in all patients. However, recovery times and activation-recovery intervals were prolonged relative to control, indicating delayed repolarization and abnormally long action potential duration (312±30 ms versus 235±21 ms in control). Activation-recovery interval prolongation was spatially heterogeneous, with repolarization gradients much steeper than control (119±19 ms/cm versus 2.0±2.0 ms/cm). There was variability in steepness and distribution of repolarization gradients between and within LQTS types. Repolarization gradients were steeper in symptomatic patients (130±27 ms/cm in 12 symptomatic patients versus 98±19 ms/cm in 13 asymptomatic patients; P<0.05).

CONCLUSIONS

LQTS patients display regions with steep repolarization dispersion caused by localized action potential duration prolongation. This defines a substrate for reentrant arrhythmias, not detectable by surface ECG. Steeper dispersion in symptomatic patients suggests a possible role for ECG imaging in risk stratification.