Selectivity filter mutation in Na 1.5 promotes ventricular tachycardia.

Unlabelled: Loss-of-Function (LoF) mutations in the gene, which encodes for the predominant cardiac Na isoform, Na 1.5 result in either deficiency in the channel expression or function. Impaired Na 1.

Distinct intracellular spatiotemporal expression of Calmodulin genes underlies functional diversity of Calmodulin-dependent signalling in cardiac myocytes.

Aims: This study aims to resolve the mechanisms underlying Calmodulin (CaM)'s signalling diversity by investigating whether the three CaM genes-Calm1, Calm2, and Calm3-play distinct or redundant roles in cardiac myocytes, focusing on their spatial mRNA localization and interactions with key targets.

Methods And Results: We utilized single-molecule mRNA detection and three-dimensional imaging to map the spatial distribution of Calm1, Calm2, and Calm3 mRNAs within ventricular myocytes. These mRNAs were found to be consistently positioned within specific cellular zones, overlapping with their target mRNAs and forming region-specific transcript conjunctions.

Intercalated Disc Abnormalities Are Linked to Arrhythmias in Inflammatory Cardiomyopathy.

Background: The relationship between intercalated disc abnormalities (IDAs) and arrhythmias in inflammatory cardiomyopathy (ICM) remains incompletely understood.

Objectives: This study presents a pilot research that aimed to: 1) investigate the link between IDAs and arrhythmias in humans with ICM; and 2) compare findings in humans and mice with experimental autoimmune myocarditis (EAM).

Methods: Humans with ICM (N = 316) investigated for either genetic or autoimmune IDAs were identified at a referral center.

Lamotrigine promotes reentrant ventricular tachycardia in murine hearts.

Objective: In 2021, the US Food and Drug Administration issued a safety warning concerning lamotrigine use in patients with underlying cardiac disorders. This warning was based on in vitro data that predicted class Ib antiarrhythmic activity for lamotrigine. Therefore, we investigated the proarrhythmic potential of lamotrigine in the murine heart and compared its effect with flecainide.

Indirect Correlative Light and Electron Microscopy (iCLEM): A Novel Pipeline for Multiscale Quantification of Structure From Molecules to Organs.

Correlative light and electron microscopy (CLEM) methods are powerful methods that combine molecular organization (from light microscopy) with ultrastructure (from electron microscopy). However, CLEM methods pose high cost/difficulty barriers to entry and have very low experimental throughput. Therefore, we have developed an indirect correlative light and electron microscopy (iCLEM) pipeline to sidestep the rate-limiting steps of CLEM (i.

Spatial Pattern Analysis using Closest Events (SPACE)-A Nearest Neighbor Point Pattern Analysis Framework for Assessing Spatial Relationships from Digital Images.

The quantitative description of biological structures is a valuable yet difficult task in the life sciences. This is commonly accomplished by imaging samples using fluorescence microscopy and analyzing resulting images using Pearson's correlation or Manders' co-occurrence intensity-based colocalization paradigms. Though conceptually and computationally simple, these approaches are critically flawed due to their reliance on signal overlap, sensitivity to cursory signal qualities, and inability to differentiate true and incidental colocalization.

Cardiac-Specific Deletion of Scn8a Mitigates Dravet Syndrome-Associated Sudden Death in Adults.

Background: Sudden unexpected death in epilepsy (SUDEP) is a fatal complication experienced by otherwise healthy epilepsy patients. Dravet syndrome (DS) is an inherited epileptic disorder resulting from loss of function of the voltage-gated sodium channel, Na 1.1, and is associated with particularly high SUDEP risk.

Vascular Endothelial Barrier Protection Prevents Atrial Fibrillation by Preserving Cardiac Nanostructure.

Background: Atrial fibrillation (AF), the most common cardiac arrhythmia, is widely associated with inflammation, vascular dysfunction, and elevated levels of the vascular leak-inducing cytokine, vascular endothelial growth factor (VEGF). Mechanisms underlying AF are poorly understood and current treatments only manage this progressive disease, rather than arresting the underlying pathology. The authors previously identified edema-induced disruption of sodium channel (NaV1.

Extracellular Perinexal Separation Is a Principal Determinant of Cardiac Conduction.

Background: Cardiac conduction is understood to occur through gap junctions. Recent evidence supports ephaptic coupling as another mechanism of electrical communication in the heart. Conduction via gap junctions predicts a direct relationship between conduction velocity (CV) and bulk extracellular resistance.

Unraveling Impacts of Chamber-Specific Differences in Intercalated Disc Ultrastructure and Molecular Organization on Cardiac Conduction.

Background: Propagation of action potentials through the heart coordinates the heartbeat. Thus, intercalated discs, specialized cell-cell contact sites that provide electrical and mechanical coupling between cardiomyocytes, are an important target for study. Impaired propagation leads to arrhythmias in many pathologies, where intercalated disc remodeling is a common finding, hence the importance and urgency of understanding propagation dependence on intercalated disc structure.

STIM1 ablation impairs exercise-induced physiological cardiac hypertrophy and dysregulates autophagy in mouse hearts.

Cardiac stromal interaction molecule 1 (STIM1), a key mediator of store-operated Ca entry (SOCE), is a known determinant of cardiomyocyte pathological growth in hypertrophic cardiomyopathy. We examined the role of STIM1 and SOCE in response to exercise-dependent physiological hypertrophy. Wild-type (WT) mice subjected to exercise training (WT-Ex) showed a significant increase in exercise capacity and heart weight compared with sedentary (WT-Sed) mice.

Unraveling Chamber-specific Differences in Intercalated Disc Ultrastructure and Molecular Organization and Their Impact on Cardiac Conduction.

During each heartbeat, the propagation of action potentials through the heart coordinates the contraction of billions of individual cardiomyocytes and is thus, a critical life process. Unsurprisingly, intercalated discs, which are cell-cell contact sites specialized to provide electrical and mechanical coupling between adjacent cardiomyocytes, have been the focus of much investigation. Slowed or disrupted propagation leads to potentially life-threatening arrhythmias in a wide range of pathologies, where intercalated disc remodeling is a common finding.

NaV1.6 dysregulation within myocardial T-tubules by D96V calmodulin enhances proarrhythmic sodium and calcium mishandling.

Calmodulin (CaM) plays critical roles in cardiomyocytes, regulating Na+ (NaV) and L-type Ca2+ channels (LTCCs). LTCC dysregulation by mutant CaMs has been implicated in action potential duration (APD) prolongation and arrhythmogenic long QT (LQT) syndrome. Intriguingly, D96V-CaM prolongs APD more than other LQT-associated CaMs despite inducing comparable levels of LTCC dysfunction, suggesting dysregulation of other depolarizing channels.

Diversity of cells and signals in the cardiovascular system.

This white paper is the outcome of the seventh UC Davis Cardiovascular Research Symposium on Systems Approach to Understanding Cardiovascular Disease and Arrhythmia. This biannual meeting aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The theme of the 2022 Symposium was 'Cell Diversity in the Cardiovascular System, cell-autonomous and cell-cell signalling'.

αCT1 peptide sensitizes glioma cells to temozolomide in a glioblastoma organoid platform.

Glioblastoma (GBM) is the most common form of brain cancer. Even with aggressive treatment, tumor recurrence is almost universal and patient prognosis is poor because many GBM cell subpopulations, especially the mesenchymal and glioma stem cell populations, are resistant to temozolomide (TMZ), the most commonly used chemotherapeutic in GBM. For this reason, there is an urgent need for the development of new therapies that can more effectively treat GBM.

Histologic, viral, and molecular correlates of heart disease in fatal COVID-19.

Cardiac manifestations are common in severe COVID-19. This study compared the histologic, viral, and molecular findings in cardiac tissue in fatal COVID-19 (n = 11) and controls (n = 11). In situ hybridization (SARS-CoV2 RNA) and immunohistochemistry for viral proteins and the host response were quantified for the samples and compared with qRTPCR and Western blot data.

Designer Extracellular Vesicles Modulate Pro-Neuronal Cell Responses and Improve Intracranial Retention.

Gene/oligonucleotide therapies have emerged as a promising strategy for the treatment of different neurological conditions. However, current methodologies for the delivery of neurogenic/neurotrophic cargo to brain and nerve tissue are fraught with caveats, including reliance on viral vectors, potential toxicity, and immune/inflammatory responses. Moreover, delivery to the central nervous system is further compounded by the low permeability of the blood brain barrier.

Cellular Size, Gap Junctions, and Sodium Channel Properties Govern Developmental Changes in Cardiac Conduction.

Electrical conduction in cardiac ventricular tissue is regulated via sodium (Na) channels and gap junctions (GJs). We and others have recently shown that Nachannels preferentially localize at the site of cell-cell junctions, the intercalated disc (ID), in adult cardiac tissue, facilitating coupling via the formation of intercellular Nananodomains, also termed ephaptic coupling (EpC). Several properties governing EpC vary with age, including Nachannel and GJ expression and distribution and cell size.

Distributed synthesis of sarcolemmal and sarcoplasmic reticulum membrane proteins in cardiac myocytes.

It is widely assumed that synthesis of membrane proteins, particularly in the heart, follows the classical secretory pathway with mRNA translation occurring in perinuclear regions followed by protein trafficking to sites of deployment. However, this view is based on studies conducted in less-specialized cells, and has not been experimentally addressed in cardiac myocytes. Therefore, we undertook direct experimental investigation of protein synthesis in cardiac tissue and isolated myocytes using single-molecule visualization techniques and a novel proximity-ligated in situ hybridization approach for visualizing ribosome-associated mRNA molecules for a specific protein species, indicative of translation sites.

The Cx43 Carboxyl-Terminal Mimetic Peptide αCT1 Protects Endothelial Barrier Function in a ZO1 Binding-Competent Manner.

The Cx43 carboxyl-terminus (CT) mimetic peptide, αCT1, originally designed to bind to Zonula Occludens 1 (ZO1) and thereby inhibit Cx43/ZO1 interaction, was used as a tool to probe the role of Cx43/ZO1 association in regulation of epithelial/endothelial barrier function. Using both in vitro and ex vivo methods of barrier function measurement, including Electric Cell-Substrate Impedance Sensing (ECIS), a TRITC-dextran Transwell permeability assay, and a FITC-dextran cardiovascular leakage protocol involving Langendorff-perfused mouse hearts, αCT1 was found to protect the endothelium from thrombin-induced breakdown in cell-cell contacts. Barrier protection was accompanied by significant remodeling of the F-actin cytoskeleton, characterized by a redistribution of F-actin away from the cytoplasmic and nuclear regions of the cell, towards the endothelial cell periphery, in association with alterations in cellular chiral orientation distribution.

Intercalated disk nanoscale structure regulates cardiac conduction.

The intercalated disk (ID) is a specialized subcellular region that provides electrical and mechanical connections between myocytes in the heart. The ID has a clearly defined passive role in cardiac tissue, transmitting mechanical forces and electrical currents between cells. Recent studies have shown that Na+ channels, the primary current responsible for cardiac excitation, are preferentially localized at the ID, particularly within nanodomains such as the gap junction-adjacent perinexus and mechanical junction-associated adhesion-excitability nodes, and that perturbations of ID structure alter cardiac conduction.