Contrasting Nav1.8 Activity in Scn10a-/- Ventricular Myocytes and the Intact Heart.

BACKGROUND: Genome-wide association studies have implicated variants in SCN10A, which encodes Nav1.8, as modulators of cardiac conduction. Follow-up work has indicated the SCN10A sequence includes an intronic enhancer for SCN5A. Yet the role of the Nav1.8 protein in the myocardium itself is still unclear. To investigate this, we use homozygous knockout mice (Scn10a-/-) generated by disruption of exons 4 and 5, leaving the Scn5a enhancer intact. METHODS AND RESULTS: We previously reported that pharmacologic blockade of Nav1.8 in wild-type animals blunts action potential prolongation by ATX-II at slow drive rates (≤1 Hz). Here we present evidence of the same blunting in Scn10a-/- compared to wild-type ventricular myocytes, supporting the conclusion that Nav1.8 contributes to late sodium current at slow rates. In contrast to earlier studies, we found no differences in electrocardiographic parameters between genotypes. Low-dose ATX-II exposure in lightly anesthetized animals and Langendorff-perfused hearts prolonged QTc and generated arrhythmias to the same extent in wild-type and Scn10a-/-. RNA sequencing failed to identify full-length Scn10a transcripts in wild-type or knockout isolated ventricular myocytes. However, loss of late current in Scn10a-/- myocytes was replicated independently in a blinded set of experiments. CONCLUSIONS: While Scn10a transcripts are not detectible in ventricular cardiomyocytes, gene deletion results in reproducible loss of late sodium current under extreme experimental conditions. However, there are no identifiable consequences of this Scn10a deletion in the intact mouse heart at usual rates. These findings argue that common variants in SCN10A that affect ventricular conduction do so by modulating SCN5A.

Electrocardiographic abnormalities and risk of developing cardiac events in extracardiac sarcoidosis.

BACKGROUND: Cardiac involvement is a leading cause of death from sarcoidosis. Because the efficacy of corticosteroid treatment is limited in patients with cardiac manifestation, early diagnosis is important. However, cardiac involvement is difficult to identify at early stages and is often underdiagnosed. Therefore, this study aimed to identify electrocardiographic risk factors for cardiac events in patients with extracardiac sarcoidosis. METHODS: This prospective observational cohort study included 227 patients with extracardiac sarcoidosis who did not have any cardiac manifestation (age, 49 ± 17 years; women, 63%). We studied the association of electrocardiographic abnormalities with developing cardiac manifestations. RESULTS: During a follow-up of 6.3 ± 3.7 years, 11 patients developed cardiac events, including advanced atrioventricular block (4 patients), ventricular tachycardia (4 patients), and systolic dysfunction (3 patients). All patients had electrocardiographic abnormalities prior to the development of cardiac events. In multivariate analyses, the baseline heart rate and PR interval were associated with increased risk of developing cardiac events. The QRS duration and corrected QT interval were not associated with cardiac manifestations. The multivariate analyses also revealed that baseline conduction disorder, ST segment/T wave abnormalities, and fragmented QRS complexes were associated with cardiac events. CONCLUSIONS: Electrocardiographic abnormalities occurred prior to cardiac events in extracardiac sarcoidosis. Patients with electrocardiographic abnormalities may require further evaluation for cardiac involvement and careful follow-up.

Expression of neuropeptide receptor mRNA during osteoblastic differentiation of mouse iPS cells.

Various studies have shown a relationship between nerves and bones. Recent evidence suggests that both sensory and sympathetic nerves affect bone metabolism; however, little is known about how neuropeptides are involved in the differentiation of pluripotent stem cells into osteoblastic (OB) cells. To evaluate the putative effects of neuropeptides during the differentiation of mouse induced pluripotent stem (iPS) cells into calcified tissue-forming OB cells, we investigated the expression patterns of neuropeptide receptors at each differentiation stage. Mouse iPS cells were seeded onto feeder cells and then transferred to low-attachment culture dishes to form embryoid bodies (EBs). EBs were cultured for 4 weeks in osteoblastic differentiation medium. The expression of α1-adrenergic receptor (AR), α2-AR, ß2-AR, neuropeptide Y1 receptor (NPY1-R), neuropeptide Y2 receptor (NPY2-R), calcitonin gene-related protein receptor (CGRP-R), and neurokinin 1-R (NK1-R) was assessed by reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR. Among these neuropeptide receptors, CGRP-R and ß2-AR were expressed at all stages of cell differentiation, including the iPS cell stage, with peak expression occurring at the early osteoblastic differentiation stage. Another sensory nervous system receptor, NK1-R, was expressed mainly in the late osteoblastic differentiation stage. Furthermore, CGRP-R mRNA showed an additional small peak corresponding to EBs cultured for 3 days, suggesting that EBs may be affected by serum CGRP. These data suggest that the sensory nervous system receptor CGRP-R and the sympathetic nervous system receptor ß2-AR may be involved in the differentiation of iPS cells into the osteoblastic lineage. It follows from these findings that CGRP and ß2-AR may regulate cell differentiation in the iPS and EB stages, and that each neuropeptide has an optimal period of influence during the differentiation process.

Smoking was a Possible Negative Predictor of Incident Hypertension After a Five-Year Follow-up Among a General Japanese Population.

BACKGROUNDS: The association between cigarette smoking and hypertension is controversial. The aim of this study is to investigate the association between smoking and incident hypertension. METHODS: This is a post-hoc five-year follow-up study in a general Japanese population. Logistic regressions were performed using incident hypertension as an outcome and smoking status as an independent predictor adjusting for sex, age, body mass index (BMI), total cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, fasting plasma glucose (FPG), drinking status, and diabetes in 1,297 subjects without hypertension at baseline. RESULTS: The incidence of hypertension was 16.9% vs. 27.6% (smokers vs. nonsmokers, P = 0.01) in men and 0.0% vs. 16.9% (smokers vs. nonsmokers, P = 0.03) in women. The odds ratio (OR) (95% confidence interval (CI)) of incident hypertension was 0.38 (0.19 - 0.76) (P = 0.006) for smokers at baseline, 0.33 (0.16 - 0.68) (P = 0.003) for continuing smokers, and 2.11 (0.33 - 13.45) (P = 0.4) for ex-smokers. Age (OR = 1.52, P < 0.0001), BMI (OR = 1.46, P < 0.0001), and FPG (OR = 1.23, P = 0.007) were other independent predictors of incident hypertension. CONCLUSIONS: Smoking was a possible significant negative predictor of incident hypertension in a general Japanese population.

Electrocardiographic characteristics and SCN5A mutations in idiopathic ventricular fibrillation associated with early repolarization.

BACKGROUND: Recently, we and others reported that early repolarization (J wave) is associated with idiopathic ventricular fibrillation. However, its clinical and genetic characteristics are unclear. METHODS AND RESULTS: This study included 50 patients (44 men; age, 45 ± 17 years) with idiopathic ventricular fibrillation associated with early repolarization, and 250 age- and sex-matched healthy controls. All of the patients had experienced arrhythmia events, and 8 (16%) had a family history of sudden death. Ventricular fibrillation was inducible by programmed electric stimulation in 15 of 29 patients (52%). The heart rate was slower and the PR interval and QRS duration were longer in patients with idiopathic ventricular fibrillation than in controls. We identified nonsynonymous variants in SCN5A (resulting in A226D, L846R, and R367H) in 3 unrelated patients. These variants occur at residues that are highly conserved across mammals. His-ventricular interval was prolonged in all of the patients carrying an SCN5A mutation. Sodium channel blocker challenge resulted in an augmentation of early repolarization or development of ventricular fibrillation in all of 3 patients, but none was diagnosed with Brugada syndrome. In heterologous expression studies, all of the mutant channels failed to generate any currents. Immunostaining revealed a trafficking defect in A226D channels and normal trafficking in R367H and L846R channels. CONCLUSIONS: We found reductions in heart rate and cardiac conduction and loss-of-function mutations in SCN5A in patients with idiopathic ventricular fibrillation associated with early repolarization. These findings support the hypothesis that decreased sodium current enhances ventricular fibrillation susceptibility.

Preexcitation unmasks J waves: 2 cases.

It is not known if J waves of early repolarization can be affected by depolarization or not. We report 2 cases in whom J waves were unmasked by preexcitation. A 59-year-old woman with Wolff-Parkinson-White syndrome who had frequent episodes of tachycardia underwent radiofrequency catheter ablation. The 12-lead electrocardiogram on admission showed delta waves and a notch in leads II, III, and aVF (J waves), which disappeared after the elimination of preexcitation. A 56-year-old man with Wolff-Parkinson-White syndrome was admitted for catheter ablation for supraventricular tachycardia. His electrocardiogram showed delta waves in I, II, aVL, V(2) to V(6), and J waves in the inferior leads and V(3) through V(6) with ST elevation and ST elevation in V(2). After ablation, J waves disappeared and were replaced by S waves. However, ST elevation remained in the precordial leads. The 2 cases suggest that J waves may be affected by the depolarization process: preexcitation.