Ion channel trafficking implications in heart failure.

Heart failure (HF) is recognized as an epidemic in the contemporary world, impacting around 1%-2% of the adult population and affecting around 6 million Americans. HF remains a major cause of mortality, morbidity, and poor quality of life. Several therapies are used to treat HF and improve the survival of patients; however, despite these substantial improvements in treating HF, the incidence of HF is increasing rapidly, posing a significant burden to human health. The total cost of care for HF is USD 69.8 billion in 2023, warranting a better understanding of the mechanisms involved in HF. Among the most serious manifestations associated with HF is arrhythmia due to the electrophysiological changes within the cardiomyocyte. Among these electrophysiological changes, disruptions in sodium and potassium currents' function and trafficking, as well as calcium handling, all of which impact arrhythmia in HF. The mechanisms responsible for the trafficking, anchoring, organization, and recycling of ion channels at the plasma membrane seem to be significant contributors to ion channels dysfunction in HF. Variants, microtubule alterations, or disturbances of anchoring proteins lead to ion channel trafficking defects and the alteration of the cardiomyocyte's electrophysiology. Understanding the mechanisms of ion channels trafficking could provide new therapeutic approaches for the treatment of HF. This review provides an overview of the recent advances in ion channel trafficking in HF.

Ethnic and racial differences in Asian populations with ion channelopathies associated with sudden cardiac death.

Cardiovascular diseases are associated with several morbidities and are the most common cause of worldwide disease-related fatalities. Studies show that treatment and outcome-related differences for cardiovascular diseases disproportionately affect minorities in the United States. The emergence of ethnic and racial differences in sudden cardiac death (SCD) and related ion channelopathies complicates cardiovascular disease prevention, diagnosis, management, prognosis, and treatment objectives for patients and physicians alike. This review compiles and synthesizes current research in cardiac ion channelopathies and genetic disorders in Asian populations, an underrepresented population in cardiovascular literature. We first present a brief introduction to SCD, noting relevant observations and statistics from around the world, including Asian populations. We then examined existing differences between Asian and White populations in research, treatment, and outcomes related to cardiac ion channelopathies and SCD, showing progression in thought and research over time for each ion channelopathy. The review also identifies research that explored phenotypic abnormalities, device usage, and risk of death in Asian patients. We touch upon the unique genetic risk factors in Asian populations that lead to cardiac ion channelopathies and SCD while comparing them to White and Western populations, particularly in the United States, where Asians comprise approximately 7% of the total population. We also propose potential solutions such as improving early genetic screening, addressing barriers affecting access to medical care and device utilization, physician training, and patient education on risks.

Challenge in Diagnosis and Management of a Patient With Myocardial Bridge and Coronary Artery Spasm.

Positive ischemia by noninvasive imaging studies often results in nonobstructive disease in cardiac catheterization. In this case, we observed ischemia by nuclear stress test in only the anteroseptal area, and the apex is free of ischemia. Coronary angiogram findings were unremarkable, but intravascular ultrasound confirmed the long length of the myocardial bridge. Further testing with spasm provocation and microvascular testing showed diffuse epicardial spasm in this area of myocardial bridge without microvascular dysfunction. We observed the myocardial bridge but no microvascular dysfunction. This case illustrates the coexistence of spasm in the area of a myocardial bridge and the challenges in the medical management of these patients. (Level of Difficulty: Advanced.).

Pathophysiology of Cav1.3 L-type calcium channels in the heart.

Ca2+ plays a crucial role in excitation-contraction coupling in cardiac myocytes. Dysfunctional Ca2+ regulation alters the force of contraction and causes cardiac arrhythmias. Ca2+ entry into cardiomyocytes is mediated mainly through L-type Ca2+ channels, leading to the subsequent Ca2+ release from the sarcoplasmic reticulum. L-type Ca2+ channels are composed of the conventional Cav1.2, ubiquitously expressed in all heart chambers, and the developmentally regulated Cav1.3, exclusively expressed in the atria, sinoatrial node, and atrioventricular node in the adult heart. As such, Cav1.3 is implicated in the pathogenesis of sinoatrial and atrioventricular node dysfunction as well as atrial fibrillation. More recently, Cav1.3 de novo expression was suggested in heart failure. Here, we review the functional role, expression levels, and regulation of Cav1.3 in the heart, including in the context of cardiac diseases. We believe that the elucidation of the functional and molecular pathways regulating Cav1.3 in the heart will assist in developing novel targeted therapeutic interventions for the aforementioned arrhythmias.

Chronic Flail Tricuspid Valve Related to Blunt Chest Trauma: A Case Report.

Tricuspid valve regurgitation (TR) is common in the adult population. A small part of this population is devoted to those who have a flail tricuspid leaflet. Flail TR can be caused by blunt chest trauma. Onset is often acute and severe and rarely seen in the form of isolated flail TR. Here, we present a rare encounter with chronic isolated tricuspid valve flail and severe TR related to blunt chest trauma.

The Abnormal Sinus Rhythm: Myxedema Coma Complicated by Subacute Cardiac Tamponade.

Subacute cardiac tamponade (SCT) is a potentially life-threatening condition that requires immediate medical attention. Combining careful history taking, focused physical exam, and the use of point of care ultrasound (POCUS) for early diagnosis with aggressive management can minimize potential complications. In patients with severe hypothyroidism and myxedema coma, clinical signs of cardiac tamponade may be masked and lead to delayed diagnosis. We present a case of a 67-year-old female with SCT secondary to myxedema coma, necessitating emergent pericardiocentesis following the identification of a large pericardial effusion with tamponade physiology. This case highlights the importance of thorough history taking with focused diagnostic workup, including POCUS in patients with an insidious presentation of SCT.

Proton Pump Inhibitors Directly Block hERG-Potassium Channel and Independently Increase the Risk of QTc Prolongation in a Large Cohort of US Veterans.

[Figure: see text].

Risk of QTc Interval Prolongation Associated With Circulating Anti-Ro/SSA Antibodies Among US Veterans: An Observational Cohort Study.

Background Anti-Sjögren's syndrome-related antigen A-antibodies (anti-Ro/SSA-antibodies) are responsible for a novel form of acquired long-QT syndrome, owing to autoimmune-mediated inhibition of cardiac human ether-a-go-go-related gene-potassium channels. However, current evidence derives only from basic mechanistic studies and relatively small sample-size clinical investigations. Hence, the aim of our study is to estimate the risk of QTc prolongation associated with the presence of anti-Ro/SSA-antibodies in a large population of unselected subjects. Methods and Results This is a retrospective observational cohort study using the Veterans Affairs Informatics and Computing Infrastructure. Participants were veterans who were tested for anti-Ro/SSA status and had an ECG. Descriptive statistics and univariate and multivariate logistic regression analyses were performed to identify risk factors for heart rate-corrected QT interval (QTc) prolongation. The study population consisted of 7339 subjects (61.4±12.2 years), 612 of whom were anti-Ro/SSA-positive (8.3%). Subjects who were anti-Ro/SSA-positive showed an increased prevalence of QTc prolongation, in the presence of other concomitant risk factors (crude odds ratios [OR], 1.67 [1.26-2.21] for QTc >470/480 ms; 2.32 [1.54-3.49] for QTc >490 ms; 2.77 [1.66-4.60] for QTc >500 ms), independent of a connective tissue disease history. Adjustments for age, sex, electrolytes, cardiovascular risk factors/diseases, and medications gradually attenuated QTc prolongation estimates, particularly when QT-prolonging drugs were added to the model. Nevertheless, stepwise-fully adjusted OR for the higher cutoffs remained significantly increased in anti-Ro/SSA-positive subjects, particularly for QTc >500 ms (2.27 [1.34-3.87]). Conclusions Anti-Ro/SSA-antibody positivity was independently associated with an increased risk of marked QTc prolongation in a large cohort of US veterans. Our data suggest that within the general population individuals who are anti-Ro/SSA-positive may represent a subgroup of patients particularly predisposed to ventricular arrhythmias/sudden cardiac death.

Autoimmune Calcium Channelopathies and Cardiac Electrical Abnormalities.

Patients with autoimmune diseases are at increased risk for developing cardiovascular diseases, and abnormal electrocardiographic findings are common. Voltage-gated calcium channels play a major role in the cardiovascular system and regulate cardiac excitability and contractility. Particularly, by virtue of their localization and expression in the heart, calcium channels modulate pace making at the sinus node, conduction at the atrioventricular node and cardiac repolarization in the working myocardium. Consequently, emerging evidence suggests that calcium channels are targets to autoantibodies in autoimmune diseases. Autoimmune-associated cardiac calcium channelopathies have been recognized in both sinus node dysfunction atrioventricular block in patients positive for anti-Ro/La antibodies, and ventricular arrhythmias in patients with dilated cardiomyopathy. In this review, we discuss mechanisms of autoimmune-associated calcium channelopathies and their relationship with the development of cardiac electrical abnormalities.

Corrigendum: Inhibitory Control in Speech Comprehension among Dai-Han Bilingual Children.

[This corrects the article on p. 1391 in vol. 8, PMID: 28861022.].

Inhibitory Control in Speech Comprehension among Dai-Han Bilingual Children.

We aimed to investigate differences in inhibitory control ability between proficient and non-proficient Dai-Han bilinguals. Two experiments used a combined stimulus-stimulus and stimulus-response compatibility paradigm for this purpose. Participants were Dai-Han bilingual primary-school students selected from a Dai-speaking town in Yunnan province, China. In Dai language interference condition, participants were asked to complete a picture category task. Results showed that the effect of attentional control for non-proficient bilinguals (NPBs) was significantly greater than that for proficient bilinguals (PBs), while the effect of response inhibition was not. This implied that a difference in inhibitory control between PBs and NPBs appeared at the attention control stage when interference by the Dai lexicon emerged. In Han language interference condition, however, participants were also asked to complete the same task. Results showed that the effect of response inhibition for NPBs was significantly greater than that for PBs, but the effect of attentional control was not. This demonstrated that a difference in inhibitory control emerged at the response inhibition stage when interference by the Han lexicon emerged. This pattern of results is opposite to previous researches, which indicated that the difference between PBs and NPBs occurred at the response inhibition stage under first language condition, whereas at the attentional control stage under second language (L2) condition. Based on these, this study suggests that Dai-Han bilinguals showed a remarkable L2 advantage. In addition, results showed that response times (RTs) of PBs were faster than RTs of NPBs while confounding variables (e.g., intelligence, etc.) were under control. This indicates that the inhibitory control ability of the PBs is superior to that of NPBs in this study.

Novel function of α1D L-type calcium channel in the atria.

Ca entry through atrial L-type Calcium channels (α1C and α1D) play an important role in muscular contraction, regulation of gene expression, and release of hormones including atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP). α1D Ca channel is exclusively expressed in atria, and has been shown to play a key role in the pathogenesis of atrial fibrillation. Recent data have shown that the small conductance calcium-activated potassium channel, SK4 is also atrial specific and also contributes prominently to the secretion of ANP and BNP. However, its functional role in the heart is still poorly understood. Here we used α1D gene heterozygous (α1D+/-) mice and HL-1 cells to determine the functional contribution of SK4 channels to α1D-dependent regulation of ANP and BNP secretion in response to endothelin (ET), and/or mechanical stretch. Immunoprecipitation with α1D specific antibody and western blotting with SK4 specific antibody on the immuno-precipitated protein complex showed a band at 50 KDa confirming the presence of SK4 in the complex and provided evidence of interaction between SK4 and α1D channels. Using RT-PCR, we observed a 2.9 fold decrease in expression of Cacna1d (gene encoding α1D) mRNA in atria from α1D+/-mice. The decrease in α1D mRNA corresponded with a 4.2 fold decrease in Kcnn4 (gene encoding SK4) mRNA from α1D+/- mice. These changes were paralleled with a 77% decrease in BNP serum levels from α1D+/- mice. When α1D was knocked down in HL-1cardiomyocytes using CRISPR/Cas9 technology, a 97% decrease in secreted BNP was observed even in cells subjected to stretch and endothelin. In conclusion, our data are first to show that α1D Ca and SK4 channels are coupled in the atria, and that deletion of α1D leads to decreased SK4 mRNA and BNP secretion providing evidence for a novel role of α1D in atrial endocrine function. Elucidating the regulatory factors that underlie the secretory function of atria will identify novel therapeutic targets for treatment and prevention of cardiac arrhythmias such as atrial fibrillation.

Induction of autoimmune response to the extracellular loop of the HERG channel pore induces QTc prolongation in guinea-pigs.

KEY POINTS: Channelopathies of autoimmune origin are novel and are associated with corrected QT (QTc) prolongation and complex ventricular arrhythmias. We have recently demonstrated that anti-SSA/Ro antibodies from patients with autoimmune diseases and with QTc prolongation on the ECG target the human ether-à-go-go-related gene (HERG) K+ channel by inhibiting the corresponding current, IKr , at the pore region. Immunization of guinea-pigs with a peptide (E-pore peptide) corresponding to the extracellular loop region connecting the S5 and S6 segments of the HERG channel induces high titres of antibodies that inhibit IKr , lengthen the action potential and cause QTc prolongation on the surface ECG. In addition, anti-SSA/Ro-positive sera from patients with connective tissue diseases showed high reactivity to the E-pore peptide. The translational impact is the development of a peptide-based approach for the diagnosis and treatment of autoimmune-associated long QT syndrome. ABSTRACT: We recently demonstrated that anti-SSA/52 kDa Ro antibodies (Abs) from patients with autoimmune diseases and corrected QT (QTc) prolongation directly target and inhibit the human ether-à-go-go-related gene (HERG) K+ channel at the extracellular pore (E-pore) region, where homology with SSA/52 kDa Ro antigen was demonstrated. We tested the hypothesis that immunization of guinea-pigs with a peptide corresponding to the E-pore region (E-pore peptide) will generate pathogenic inhibitory Abs and cause QTc prolongation. Guinea-pigs were immunized with a 31-amino-acid peptide corresponding to the E-pore region of HERG. On days 10-62 after immunization, ECGs were recorded and blood was sampled for the detection of E-pore peptide Abs. Serum samples from patients with autoimmune diseases were evaluated for reactivity to E-pore peptide by enzyme-linked immunosorbent assay (ELISA), and histology was performed on hearts using Masson's Trichrome. Inhibition of the HERG channel was assessed by electrophysiology and by computational modelling of the human ventricular action potential. The ELISA results revealed the presence of high titres of E-pore peptide Abs and significant QTc prolongation after immunization. High reactivity to E-pore peptide was found using anti-SSA/Ro Ab-positive sera from patients with QTc prolongation. Histological data showed no evidence of fibrosis in immunized hearts. Simulations of simultaneous inhibition of repolarizing currents by anti-SSA/Ro Ab-positive sera showed the predominance of the HERG channel in controlling action potential duration and the QT interval. These results are the first to demonstrate that inhibitory Abs to the HERG E-pore region induce QTc prolongation in immunized guinea-pigs by targeting the HERG channel independently from fibrosis. The reactivity of anti-SSA/Ro Ab-positive sera from patients with connective tissue diseases with the E-pore peptide opens novel pharmacotherapeutic avenues in the diagnosis and management of autoimmune-associated QTc prolongation.

Pathogenesis of the Novel Autoimmune-Associated Long-QT Syndrome.

BACKGROUND: Emerging clinical evidence demonstrates high prevalence of QTc prolongation and complex ventricular arrhythmias in patients with anti-Ro antibody (anti-Ro Ab)-positive autoimmune diseases. We tested the hypothesis that anti-Ro Abs target the HERG (human ether-a-go-go-related gene) K(+) channel, which conducts the rapidly activating delayed K(+) current, IKr, thereby causing delayed repolarization seen as QT interval prolongation on the ECG. METHODS AND RESULTS: Anti-Ro Ab-positive sera, purified IgG, and affinity-purified anti-52kDa Ro Abs from patients with autoimmune diseases and QTc prolongation were tested on IKr using HEK293 cells expressing HERG channel and native cardiac myocytes. Electrophysiological and biochemical data demonstrate that anti-Ro Abs inhibit IKr to prolong action potential duration by directly binding to the HERG channel protein. The 52-kDa Ro antigen-immunized guinea pigs showed QTc prolongation on ECG after developing high titers of anti-Ro Abs, which inhibited native IKr and cross-reacted with guinea pig ERG channel. CONCLUSIONS: The data establish that anti-Ro Abs from patients with autoimmune diseases inhibit IKr by cross-reacting with the HERG channel likely at the pore region where homology between anti-52-kDa Ro antigen and HERG channel is present. The animal model of autoimmune-associated QTc prolongation is the first to provide strong evidence for a pathogenic role of anti-Ro Abs in the development of QTc prolongation. It is proposed that adult patients with anti-Ro Abs may benefit from routine ECG screening and that those with QTc prolongation should receive counseling about drugs that may increase the risk for life-threatening arrhythmias.

Calreticulin negatively regulates the surface expression of Cav1.3 L-type calcium channel.

BACKGROUND: The neuroendocrine Cav1.3 L-type Ca channels have been recently found in the Human fetal heart and shown to play a vital role in Ca entry from the sarcolemma into the cell and in Ca homeostasis. Calreticulin, a Ca binding endoplasmic reticulum (ER) resident protein, has been recently shown to translocate to the cell surface where its role and function are just emerging. Here, we demonstrated a novel mechanism of Cav1.3 and calreticulin interaction resulting in downregulation of Cav1.3 channel densities in native Human fetal cardiac cells and Human Embryonic Kidney cell lines (tsA201). METHODS AND RESULTS: Cell surface and cytoplasmic staining of calreticulin was demonstrated first in cultured human fetal cardiomyocytes (HFC), gestational age 18-24 weeks, using confocal microscopy thereby establishing that calreticulin is present at the cell surface in HFC. Co-immunoprecipitation from HFC using anti-Cav1.3 Ca channel antibody, and probing with anti-calreticulin antibody revealed a 46 kDa band corresponding to calreticulin suggesting that Cav1.3 Ca channel and calreticulin co-assemble in a macromolecular complex. Co-expression of Cav1.3 and calreticulin in tsA201 cells resulted in a decrease in surface expression of Cav1.3 Ca channels. These findings were consistent with the electrophysiological studies showing that co-transfection of Cav1.3 Ca channel and calreticulin resulted in 55% reduction of Cav1.3 Ca current densities recorded from tsA201 cells. CONCLUSIONS: The results show the first evidence that calreticulin: (1) is localized outside the ER on the cell surface of HFC; (2) coimmunoprecipitates with Cav1.3 L-type Ca channel; (3) negatively regulates Cav1.3 surface expression thus resulting in decreased Cav1.3 Ca current densities. The data demonstrate a novel mechanism of modulation of Cav1.3 Ca channel by calreticulin, which may be involved in pathological settings such as autoimmune associated congenital heart block where Cav1.3 Ca channels are downregulated.

Activation of εPKC reduces reperfusion arrhythmias and improves recovery from ischemia: optical mapping of activation patterns in the isolated guinea-pig heart.

UNLABELLED: Pervious biochemical and hemodynamic studies have highlighted the important role of εPKC in cardioprotection during ischemic preconditioning. However, little is known about the electrophysiological consequences of εPKC modulation in ischemic hearts. Membrane permeable peptide εPKC selective activator and inhibitor were used to investigate the role of εPKC modulation in reperfusion arrhythmias. METHODS: Protein transduction domain from HIV-TAT was used as a carrier for peptide delivery into intact Langendorff perfused guinea pig hearts. Action potentials were imaged and mapped (124 sites) using optical techniques and surface ECG was continuously recorded. Hearts were exposed to 30 min stabilization period, 15 min of no-flow ischemia, followed by 20 min reperfusion. Peptides (0.5 µM) were infused as follows: (a) control (vehicle-TAT peptide; TAT-scrambled ψεRACK peptide); (b) εPKC agonist (TAT-ψεRACK); (c) εPKC antagonist (TAT-εV1). RESULTS: Hearts treated with εPKC agonist ψεRACK had reduced incidence of ventricular tachycardia (VT, 64%) and fibrillation (VF, 50%) compared to control (VT, 80%, P<0.05) and (VF, 70%, P < 0.05). However, the highest incidence of VT (100%, P < 0.05) and VF (80%) occurred in hearts treated with εPKC antagonist peptide εV1 compared to control and to εPKC agonist ψεRACK. Interestingly, at 20 min reperfusion, 100% of hearts treated with εPKC agonist ψεRACK exhibited complete recovery of action potentials compared to 40% (P < 0.05) of hearts treated with εPKC antagonist peptide, εV1 and 65% (P < 0.5) of hearts in control. At 20 min reperfusion, maps of action potential duration from εPKC agonist ψεRACK showed minimal dispersion (48.2 ± 9 ms) compared to exacerbated dispersion (115.4 ± 42 ms, P < 0.05) in εPKC antagonist and control (67 ± 20 ms, P<0.05). VT/VF and dispersion from hearts treated with scrambled agonist or antagonist peptides were similar to control. CONCLUSION: The results demonstrate that εPKC activation by ψεRACK peptide protects intact hearts from reperfusion arrhythmias and affords better recovery. On the other hand, inhibition of εPKC increased the incidence of arrhythmias and worsened recovery compared to controls. The results carry significant therapeutic implications for the treatment of acute ischemic heart disease by preconditioning-mimicking agents.

Rescue and worsening of congenital heart block-associated electrocardiographic abnormalities in two transgenic mice.

INTRODUCTION: Congenital heart block (CHB) is a passively acquired autoimmune disease considered to be due to the transfer of maternal autoantibodies, anti-SSA/Ro -SSB/La, to the fetus resulting in atrioventricular (AV) block and sinus bradycardia. We previously established a murine model for CHB where pups born to immunized wild-type (WT) mothers exhibited electrocardiographic abnormalities similar to those seen in CHB and demonstrated inhibition of L-type Ca channels (LTCCs) by maternal antibodies. Here, we hypothesize that overexpression of LTCC should rescue, whereas knockout of LTCC should worsen the electrocardiographic abnormalities in mice. METHODS AND RESULTS: Transgenic (TG) mice were immunized with SSA/Ro and SSB/La antigens. Pups born to immunized WT mothers had significantly greater sinus bradycardia and AV block compared to pups from nonimmunized WT. TG pups overexpressing LTCC had significantly less sinus bradycardia and AV block compared to their non-TG littermates and to pups born to immunized WT mothers. All LTCC knockout pups born to immunized mothers had sinus bradycardia, advanced degree of AV block, and decreased fetal parity. No sinus bradycardia or AV block were manifested in pups from control nonimmunized WT mothers. IgG from mothers with CHB children, but not normal IgG, completely inhibited intracellular Ca transient ([Ca](i)T) amplitude. CONCLUSIONS: Cardiac-specific overexpression of LTCC significantly reduced the incidence of AV block and sinus bradycardia in pups exposed to anti-SSA/Ro -SSB/La autoantibodies, whereas exposure of LTCC knockout pups to these autoantibodies significantly worsened the electrocardiographic abnormalities. These findings support the hypothesis that maternal antibodies inhibit LTCC and [Ca](i)T thus contributing to the development of CHB. Altogether, the results are relevant to the development of novel therapies for CHB.