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.

The development of high-throughput automated patch-clamp technology is a recent breakthrough in the field of Brugada syndrome research. Brugada syndrome is a heart disorder marked by abnormal electrocardiographic readings and an elevated risk of sudden cardiac death due to arrhythmias. Various experimental models, developed either in animals, cell lines, human tissue or computational simulation, play a crucial role in advancing our understanding of this condition, and developing effective treatments. In the perspective of the pathophysiological role of ion channels and their pharmacology, automated patch-clamp involves a robotic system that enables the simultaneous recording of electrical activity from multiple single cells at once, greatly improving the speed and efficiency of data collection. By combining this approach with the use of patient-derived cardiomyocytes, researchers are gaining a more comprehensive view of the underlying mechanisms of heart disease. This has led to the development of more effective treatments for those affected by cardiovascular conditions.

Aim: Striatin (Strn) is a scaffold protein expressed in cardiomyocytes (CMs) and alteration of its expression are described in various cardiac diseases. However, the alteration underlying its pathogenicity have been poorly investigated.Methods: We studied the role(s) of cardiac Strn gene (STRN) by comparing the functional properties of CMs, generated from Strn‐KO and isogenic WT mouse embryonic stem cell lines.Results: The spontaneous beating rate of Strn‐KO CMs was faster than WT cells, and this correlated with a larger fast I_Na conductance and no changes in I_f. Paced (2–8 Hz) Strn‐KO CMs showed prolonged action potential (AP) duration in comparison with WT CMs and this was not associated with changes in I_CaL and I_Kr. Motion video tracking analysis highlighted an altered contraction in Strn‐KO CMs; this was associated with a global increase in intracellular Ca²⁺, caused by an enhanced late Na⁺ current density (I_NaL) and a reduced Na⁺/Ca²⁺ exchanger (NCX) activity and expression. Immunofluorescence analysis confirmed the higher Na⁺ channel expression and a more dynamic microtubule network in Strn‐KO CMs than in WT. Indeed, incubation of Strn‐KO CMs with the microtubule stabilizer taxol, induced a rescue (downregulation) of I_Na conductance toward WT levels.Conclusion: Loss of STRN alters CMs electrical and contractile profiles and affects cell functionality by a disarrangement of Strn‐related multi‐protein complexes. This leads to impaired microtubules dynamics and Na⁺ channels trafficking to the plasma membrane, causing a global Na⁺ and Ca²⁺ enhancement.

Background and Aims Patients with metastatic breast cancer have an increased risk of sudden cardiac death (SCD) that cannot be fully explained by cardiotoxic treatments. Recent evidence shows that autoantibodies targeting the cardiac NaV1.5 sodium channel in Brugada syndrome (BrS) can trigger arrhythmias and elevate SCD risk. Similarly, autoantibodies against the neonatal NaV1.5 isoform have been found in metastatic breast cancer patients. Given the high homology between these NaV1.5 isoforms, we investigated whether these autoantibodies cross-react with the cardiac isoform, potentially contributing to SCD in this population. Methods Plasma from twenty metastatic breast cancer patients was analyzed for anti-NaV1.5 autoantibodies using HEK293A cells expressing the NaV1.5 protein, followed by Western blotting. The effects of these autoantibodies on sodium current density were assessed in cellular models and wild-type mice, with electrocardiographic monitoring after plasma infusion. Results Fifteen plasma samples from metastatic breast cancer patients tested positive for anti-NaV1.5 autoantibodies, significantly reducing sodium current density in vitro. Mice injected with these plasma samples developed severe arrhythmias and a Brugada syndrome-like ECG pattern. In contrast, plasma samples either without the autoantibodies or with IgG depletion showed no such effects, underscoring the role of IgG in sodium current reduction and confirming the pathogenicity of the autoantibodies. Conclusions This study demonstrates that anti-NaV1.5 autoantibodies in metastatic breast cancer patients can cross-react with the cardiac NaV1.5 isoform, potentially leading to fatal arrhythmias. These findings highlight a novel mechanism for the high SCD rate in this population and suggest that therapies involving sodium blockers should be used with caution to avoid exacerbating this risk. Reliable diagnostic tests and targeted therapies are urgently needed to mitigate SCD risk in affected patients.

Aims: Immunoglobulin light chain (AL) amyloidosis is a protein misfolding disease characterized by the systemic deposition of amyloid fibrils derived from monoclonal light chains (LCs). Cardiac involvement is the major determinant of prognosis and mortality, and beyond fibril accumulation, soluble cardiotoxic LCs play a critical role in disease progression. While current in vivo models like C. elegans and murine systems have demonstrated LC toxicity, they lack human relevance or fail to capture soluble LC-induced cardiotoxicity. This study aimed to characterize the electrophysiological effects of cardiotoxic LCs on a human-relevant model using human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Methods and Results: Two amyloidogenic cardiotoxic LCs (H3 and H6) from AL patients and one non-cardiotoxic LC (M10) from a multiple myeloma patient were biophysically characterized and tested in hiPSC-CMs at clinically relevant concentrations. Electrophysiological recordings revealed that H3 and H6 significantly reduced spontaneous action potential (AP) firing frequency and maximal upstroke velocity (dV/dt) in hiPSC-CMs, indicating impaired excitability. H6 also shortened AP duration. H3 exposure led to a ∼40% reduction in peak sodium current density and altered inactivation kinetics of the L-type calcium current, without affecting major pacemaker or repolarizing potassium (I _Kr or I _Ks ) currents. In contrast, M10 had no effect on any measured parameter, validating the model’s ability to discriminate toxic from non-toxic LCs. Conclusion: This study demonstrates that hiPSC-CMs provide a clinically relevant human model to investigate LC-induced cardiotoxicity. Cardiotoxic LCs exert distinct but converging electrophysiological impairments, including disruption of sodium and L-type calcium currents, contributing to reduced excitability and altered AP morphology. These findings provide mechanistic insights into AL amyloidosis-related cardiac dysfunction and establish a foundation for future therapeutic screening targeting soluble LC toxicity in a human context.