Isolated Left Atrium Morphofunctional Study of an Experimental Pulmonary Hypertension Model in Rats. / Estudo Morfofuncional do Átrio Esquerdo Isolado de um Modelo Experimental de Hipertensão Pulmonar em Ratos.

BACKGROUND: The high incidence of atrial arrhythmias in pulmonary hypertension (PH) might be associated with poor prognosis, and the left atrium (LA) may play a role in this. An important finding in PH studies is that LA remodeling is underestimated. OBJECTIVE: This study investigated LA morphology and mechanical function, as well as the susceptibility to develop arrhythmias in a monocrotaline-induced PH (MCT-PH) model. METHODS: Wistar rats aged 4 weeks received 50 mg/kg of MCT. Electrocardiography and histology analysis were performed to evaluate the establishment of the MCT-PH model. The tissue was mounted in an isolated organ bath to characterize the LA mechanical function. RESULTS: Compared with the control group (CTRL), the MCT-PH model presented LA hypertrophy and changes in cardiac electrical activity, as evidenced by increased P wave duration, PR and QT interval in MCT-PH rats. In LA isolated from MCT-PH rats, no alteration in inotropism was observed; however, the time to peak contraction was delayed in the experimental MCT-PH group. Finally, there was no difference in arrhythmia susceptibility of LA from MCT-PH animals after the burst pacing protocol. CONCLUSION: The morphofunctional remodeling of the LA did not lead to increased susceptibility to ex vivo arrhythmia after application of the burst pacing protocol.

FUNDAMENTO: A alta incidência de arritmias atriais na hipertensão pulmonar (HP) pode estar associada a um prognóstico ruim, e o átrio esquerdo (AE) pode desempenhar um papel neste quadro. Um achado importante nos estudos de HP é que a remodelação do AE é subestimada. OBJETIVO: Este estudo investigou a morfologia e a função mecânica do AE, bem como a suscetibilidade ao desenvolvimento de arritmias em um modelo de HP induzida por monocrotalina (HP-MCT). MÉTODOS: Ratos Wistar com 4 semanas de idade receberam 50 mg/kg de MCT. Foram realizadas análises eletrocardiográficas e histológicas para avaliar o estabelecimento do modelo de HP-MCT. O tecido foi montado em banho de órgão isolado para caracterizar a função mecânica do AE. RESULTADOS: Em comparação com o grupo controle, o modelo de HP-MCT apresentou hipertrofia do AE e alterações da atividade elétrica cardíaca, conforme evidenciadas pelo aumento da duração da onda P, PR e intervalo QT. Não foi observada alteração no inotropismo do AE isolado de ratos com HP-MCT; no entanto, o tempo para atingir a contração máxima foi atrasado. Finalmente, não observamos diferença na suscetibilidade à arritmia no AE dos ratos com HP-MCT após o protocolo de estimulação intermitente. CONCLUSÃO: A remodelação morfofuncional do AE não levou ao aumento da suscetibilidade à arritmia ex vivo após a aplicação do protocolo de estimulação intermitente.

The fungicide tebuconazole modulates the sodium current of human NaV1.5 channels expressed in HEK293 cells.

The fungicide Tebuconazole is a widely used pesticide in agriculture and may cause cardiotoxicity. In our present investigation the effect of Tebuconazole on the sodium current (INa) of human cardiac sodium channels (NaV1.5) was studied using a heterologous expression system and whole-cell patch-clamp techniques. Tebuconazole reduced the amplitude of the peak INa in a concentration- and voltage-dependent manner. At the holding potential of -120 mV the IC50 was estimated at 204.1 ± 34.3 µM, while at -80 mV the IC50 was 0.3 ± 0.1 µM. The effect of the fungicide is more pronounced at more depolarized potentials, indicating a state-dependent interaction. Tebuconazole caused a negative shift in the half-maximal inactivation voltage and delayed recovery from fast inactivation of INa. Also, it enhanced closed-state inactivation, exhibited use-dependent block in a voltage-dependent manner. Furthermore, Tebuconazole reduced the increase in late sodium current induced by the pyrethroid insecticide ß-Cyfluthrin. These results suggest that Tebuconazole can interact with NaV1.5 channels and modulate INa. The observed effects may lead to decreased cardiac excitability through reduced INa availability, which could be a new mechanism of cardiotoxicity to be attributed to the fungicide.

Evaluation of right atrium structure and function in a rat model of monocrotaline-induced pulmonary hypertension: Exploring the possible antiarrhythmic properties of amiodarone.

Atrial arrhythmias (AA) are common in pulmonary hypertension (PH) and are closely associated with poor clinical outcomes. One of the most studied models to investigate PH is the rat model of monocrotaline (MCT) induced PH (MCT-PH). To date, little is known about right atrium (RA) function in the MCT-PH model and the propensity of RA to develop arrhythmias. Therefore, the aim of the study was to evaluate the function of the RA of control (CTRL) and MCT treated rats, and the ability of amiodarone, a classical antiarrhythmic, to prevent the occurrence of AA in the RA in MCT-PH rats. RA function was studied in MCT-PH rats 20 days after a single subcutaneous injection of MCT 50 mg/kg. The histological results indicated the presence of RA and right ventricular hypertrophy. Surface electrocardiogram demonstrated increased P wave duration, PR wave duration and QT interval in MCT rats. RA from MCT rats were more susceptible to develop ex vivo burst pacing arrhythmias when compared to CTRL. Intriguingly, amiodarone in clinical relevant concentration was not able to prevent the occurrence arrhythmias in RA from MCT-PH animals. Hence, we conclude that the rat model of MCT-PH impairs RA structure and function, and acute exposure of RA to amiodarone in clinical relevant concentration is not able to attenuate the onset of arrhythmias in the ex vivo RA preparation.

Estudo Morfofuncional do Átrio Esquerdo Isolado de um Modelo Experimental de Hipertensão Pulmonar em Ratos / Isolated Left Atrium Morphofunctional Study of an Experimental Pulmonary Hypertension Model in Rats

Resumo Fundamento A alta incidência de arritmias atriais na hipertensão pulmonar (HP) pode estar associada a um prognóstico ruim, e o átrio esquerdo (AE) pode desempenhar um papel neste quadro. Um achado importante nos estudos de HP é que a remodelação do AE é subestimada. Objetivo Este estudo investigou a morfologia e a função mecânica do AE, bem como a suscetibilidade ao desenvolvimento de arritmias em um modelo de HP induzida por monocrotalina (HP-MCT). Métodos Ratos Wistar com 4 semanas de idade receberam 50 mg/kg de MCT. Foram realizadas análises eletrocardiográficas e histológicas para avaliar o estabelecimento do modelo de HP-MCT. O tecido foi montado em banho de órgão isolado para caracterizar a função mecânica do AE. Resultados Em comparação com o grupo controle, o modelo de HP-MCT apresentou hipertrofia do AE e alterações da atividade elétrica cardíaca, conforme evidenciadas pelo aumento da duração da onda P, PR e intervalo QT. Não foi observada alteração no inotropismo do AE isolado de ratos com HP-MCT; no entanto, o tempo para atingir a contração máxima foi atrasado. Finalmente, não observamos diferença na suscetibilidade à arritmia no AE dos ratos com HP-MCT após o protocolo de estimulação intermitente. Conclusão A remodelação morfofuncional do AE não levou ao aumento da suscetibilidade à arritmia ex vivo após a aplicação do protocolo de estimulação intermitente.

Abstract Background The high incidence of atrial arrhythmias in pulmonary hypertension (PH) might be associated with poor prognosis, and the left atrium (LA) may play a role in this. An important finding in PH studies is that LA remodeling is underestimated. Objective This study investigated LA morphology and mechanical function, as well as the susceptibility to develop arrhythmias in a monocrotaline-induced PH (MCT-PH) model. Methods Wistar rats aged 4 weeks received 50 mg/kg of MCT. Electrocardiography and histology analysis were performed to evaluate the establishment of the MCT-PH model. The tissue was mounted in an isolated organ bath to characterize the LA mechanical function Results Compared with the control group (CTRL), the MCT-PH model presented LA hypertrophy and changes in cardiac electrical activity, as evidenced by increased P wave duration, PR and QT interval in MCT-PH rats. In LA isolated from MCT-PH rats, no alteration in inotropism was observed; however, the time to peak contraction was delayed in the experimental MCT-PH group. Finally, there was no difference in arrhythmia susceptibility of LA from MCT-PH animals after the burst pacing protocol. Conclusion The morphofunctional remodeling of the LA did not lead to increased susceptibility to ex vivo arrhythmia after application of the burst pacing protocol.

Experimental hypothyroidism induces cardiac arrhythmias and ranolazine reverts and prevents the phenotype.

AIMS: Hypothyroidism is associated with an increased risk of cardiovascular disease and enhanced susceptibility to arrhythmias. In our investigation, we evaluated the potential involvement of late sodium current (INa,late) in cardiac arrhythmias in an experimental murine model of hypothyroidism. MAIN METHODS: Male Swiss mice were treated with methimazole (0.1 % w/vol, during 21 days) to induce experimental hypothyroidism before ECG, action potential (AP) and intracellular Ca2+ dynamics were evaluated. Susceptibility to arrhythmia was measured in vitro and in vivo. KEY FINDINGS: The results revealed that hypothyroid animals presented ECG alterations (e.g. increased QTc) with the presence of spontaneous sustained ventricular tachycardia. These changes were associated with depolarized resting membrane potential in isolated cardiomyocytes and increased AP duration and dispersion at 90 % of the repolarization. Aberrant AP waveforms were related to increased Ca2+ sparks and out-of-pace Ca2+ waves. These changes were observed in a scenario of enhanced INa,late. Interestingly, ranolazine, a clinically used blocker of INa,late, restored the ECG alterations, reduced Ca2+ sparks and aberrant waves, decreased the in vitro events and the severity of arrhythmias observed in isolated cardiomyocytes from hypothyroid animals. Using the in vivo dobutamine + caffeine protocol, animals with hypothyroidism developed catecholaminergic bidirectional ventricular tachycardia, but pre-treatment with ranolazine prevented this. SIGNIFICANCE: We concluded that animals with hypothyroidism have increased susceptibility to developing arrhythmias and ranolazine, a clinically used blocker of INa,late, is able to correct the arrhythmic phenotype.

Eugenol interacts with cardiac sodium channel and reduces heart excitability and arrhythmias.

AIMS: Eugenol is a natural compound found in the essential oils of many aromatic plants. The compound is used as a local anesthetic because of its inhibitory effect on the voltage-gated Na+ channels (Nav), which are expressed in the nociceptive neurons. Eugenol has shown wide range of activities in the cardiovascular system; most of these activities are attributed to the modulation of voltage-sensitive Ca2+ channels. However, its action on Nav1.5, the main subtype of Nav expressed in the mammalian myocardium, is unknown. The interaction of eugenol with Nav1.5 could also contribute to its antiarrhythmic properties in vitro and ex vivo. We investigated the compound's effect on sodium current (INa) and its possible cardiac antiarrhythmic activity. METHODS: The effect of eugenol on cardiac contractility was investigated using isolated atrium from guinea pig (for isometric force measurements). The compound's effect on INa was evaluated using human embryonic cell transiently expressing human Nav1.5 and patch-clamp technique. KEY FINDINGS: Eugenol caused negative inotropic and chronotropic effects in the atria. In the ex vivo arrhythmia model, eugenol decreased atrial pacing disturbance induced by ouabain. Eugenol reduced the INa in a concentration-dependent manner. Furthermore, the compound left-shifted the stationary inactivation curve, delayed recovery from inactivation of the INa, and preferentially blocked the channel in the inactivated state. Importantly, eugenol was able to attenuate the late sodium current. All these aspects are considered to be antiarrhythmic. SIGNIFICANCE: Overall, our findings demonstrate that eugenol has antiarrhythmic activity due, at least in part, to its interaction with Nav1.5.

Ethnic-Related Sodium Voltage-Gated Channel α Subunit 5 Polymorphisms Shape the In Vitro Pharmacological Action of Amiodarone upon Nav1.5.

Nav1.5-derived Na+ current (INa) exerts a pivotal role in the depolarization phase of cardiomyocytes' action potential, and, therefore, changes in INa can contribute to fatal arrhythmias. Nav1.5 displays naturally occurring ethnicity-related polymorphisms, which might alter the functioning and pharmacology of the channel. Some studies have shown how single-nucleotide polymorphism can change the response to antiarrhythmic drugs. Investigations on the role of Nav1.5 in arrhythmogenesis associated with its functional polymorphisms are currently growing as well as the possible variability in the antiarrhythmic pharmacotherapy among ethnic groups. The influence of the ethnicity-related polymorphisms (S524Y, S1103Y, R1193Q, V1951L) on the responsiveness, selectivity, and pharmacological efficacy of the clinically used antiarrhythmic amiodarone (AMIO) is not completely known. Our objectives were to analyze biophysical and pharmacological aspects of four ethnicity-related polymorphisms before and after exposure to AMIO. Polymorphisms caused reduced AMIO potency compared with wild type (WT), which can vary by up to 4× between them. AMIO shifted the voltage dependency for current inactivation without significant effect in voltage-dependent activation to a similar extent in WT and polymorphisms. The recovery from inactivation was altered between the polymorphisms when compared with WT. Finally, the use dependency of AMIO differed between studied groups, especially at a more depolarized cell membrane. Thus, our work may guide future studies focusing on the efficiency of AMIO in treating different arrhythmias and establish more individualized guidelines for its use depending on the Nav1.5 polymorphism after validating our findings using in vivo studies. SIGNIFICANCE STATEMENT: Sodium voltage-gated channel α subunit 5 (SCN5A) gene encodes the α subunit of Nav1.5, the main cardiac voltage-gated Na+ channel. Interestingly, ethnicity-related polymorphisms are found in SCN5A. Amiodarone is used in clinical practice, and some of its effects are attributed to interaction with Nav1.5. Important, amiodarone efficacy is variable among patients. Here we show that ethnicity-related SCN5A polymorphisms lead to altered Nav1.5-amiodarone interaction, which may be the cause for the variable efficacy observed in clinical usage of amiodarone.

Cardiac electrical remodeling and neurodegenerative diseases association.

Cardiac impairment contributes significantly to the mortality associated with several neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), primarily recognized as brain pathologies. These diseases may be caused by aggregation of a misfolded protein, most often, in the brain, although new evidence also reveals peripheral abnormalities. After characterization of the cardiac involvement in neurodegenerative diseases, several studies concentrated on elucidating the cause of the impaired cardiac function. However, most of the current knowledge is focused on the mechanical aspects of the heart rather than the electrical disturbances. The main objective of this review is to summarize the most recent advances in the elucidation of cardiac electrical remodeling in the neurodegenerative environment. We aimed to determine a crosstalk between the heart and the brain in three neurodegenerative conditions: AD, PD, and HD. We found that the most studies demonstrated important alterations in the electrocardiogram (ECG) of patients with neurodegeneration and in animal models of the conditions. We also showed that little is described when considering excitability disruptions in cardiomyocytes, for example, action potential impairments. It is a matter of contention whether central nervous system abnormalities or the peripheral ones increase the risk of heart diseases in patients with neurodegenerative conditions. To determine this notion, there is a need for new heart studies focusing specifically on the cardiac electrophysiology (e.g., ECG and cardiomyocyte excitability). This review could serve as an important guide in designing novel accurate approaches targeting the heart in neuronal conditions.

Correction: Reactive oxygen species and nitric oxide imbalances lead to in vivo and in vitro arrhythmogenic phenotype in acute phase of experimental Chagas disease.

[This corrects the article DOI: 10.1371/journal.ppat.1008379.].

Reactive oxygen species and nitric oxide imbalances lead to in vivo and in vitro arrhythmogenic phenotype in acute phase of experimental Chagas disease.

Chagas Disease (CD) is one of the leading causes of heart failure and sudden death in Latin America. Treatments with antioxidants have provided promising alternatives to ameliorate CD. However, the specific roles of major reactive oxygen species (ROS) sources, including NADPH-oxidase 2 (NOX2), mitochondrial-derived ROS and nitric oxide (NO) in the progression or resolution of CD are yet to be elucidated. We used C57BL/6 (WT) and a gp91PHOX knockout mice (PHOX-/-), lacking functional NOX2, to investigate the effects of ablation of NOX2-derived ROS production on the outcome of acute chagasic cardiomyopathy. Infected PHOX-/- cardiomyocytes displayed an overall pro-arrhythmic phenotype, notably with higher arrhythmia incidence on ECG that was followed by higher number of early afterdepolarizations (EAD) and 2.5-fold increase in action potential (AP) duration alternans, compared to AP from infected WT mice. Furthermore, infected PHOX-/- cardiomyocytes display increased diastolic [Ca2+], aberrant Ca2+ transient and reduced Ca2+ transient amplitude. Cardiomyocyte contraction is reduced in infected WT and PHOX-/- mice, to a similar extent. Nevertheless, only infected PHOX-/- isolated cardiomyocytes displayed significant increase in non-triggered extra contractions (appearing in ~75% of cells). Electro-mechanical remodeling of infected PHOX-/-cardiomyocytes is associated with increase in NO and mitochondria-derived ROS production. Notably, EADs, AP duration alternans and in vivo arrhythmias were reverted by pre-incubation with nitric oxide synthase inhibitor L-NAME. Overall our data show for the first time that lack of NOX2-derived ROS promoted a pro-arrhythmic phenotype in the heart, in which the crosstalk between ROS and NO could play an important role in regulating cardiomyocyte electro-mechanical function during acute CD. Future studies designed to evaluate the potential role of NOX2-derived ROS in the chronic phase of CD could open new and more specific therapeutic strategies to treat CD and prevent deaths due to heart complications.

Increased oxidative stress and CaMKII activity contribute to electro-mechanical defects in cardiomyocytes from a murine model of Huntington's disease.

Huntington's disease (HD) is a neurodegenerative genetic disorder. Although described as a brain pathology, there is evidence suggesting that defects in other systems can contribute to disease progression. In line with this, cardiovascular defects are a major cause of death in HD. To date, relatively little is known about the peripheral abnormalities associated with the disease. Here, we applied a range of assays to evaluate cardiac electro-mechanical properties in vivo, using a previously characterized mouse model of HD (BACHD), and in vitro, using cardiomyocytes isolated from the same mice. We observed conduction disturbances including QT interval prolongation in BACHD mice, indicative of cardiac dysfunction. Cardiomyocytes from these mice demonstrated cellular electro-mechanical abnormalities, including a prolonged action potential, arrhythmic contractions, and relaxation disturbances. Cellular arrhythmia was accompanied by an increase in calcium waves and increased Ca2+ /calmodulin-dependent protein kinase II activity, suggesting that disruption of calcium homeostasis plays a key part. We also described structural abnormalities in the mitochondria of BACHD-derived cardiomyocytes, indicative of oxidative stress. Consistent with this, imbalances in superoxide dismutase and glutathione peroxidase activities were detected. Our data provide an in vivo demonstration of cardiac abnormalities in HD together with new insights into the cellular mechanistic basis, providing a possible explanation for the higher cardiovascular risk in HD.

Muscle atrophy is associated with cervical spinal motoneuron loss in BACHD mouse model for Huntington's disease.

Involuntary choreiform movements are clinical hallmark of Huntington's disease, an autosomal dominant neurodegenerative disorder caused by an increased number of CAG trinucleotide repeats in the huntingtin gene. Involuntary movements start with an impairment of facial muscles and then affect trunk and limbs muscles. Huntington's disease symptoms are caused by changes in cortex and striatum neurons induced by mutated huntingtin protein. However, little is known about the impact of this abnormal protein in spinal cord motoneurons that control movement. Therefore, in this study we evaluated abnormalities in the motor unit (spinal cervical motoneurons, motor axons, neuromuscular junctions and muscle) in a mouse model for Huntington's disease (BACHD). Using light, fluorescence, confocal, and electron microscopy, we showed significant changes such as muscle fibers atrophy, fragmentation of neuromuscular junctions, axonal alterations, and motoneurons death in BACHD mice. Noteworthy, the surviving motoneurons from BACHD spinal cords were smaller than WT. We suggest that this loss of larger putative motoneurons is accompanied by a decrease in the expression of fast glycolytic muscle fibers in this model for Huntington's disease. These observations show spinal cord motoneurons loss in BACHD that might help to understand neuromuscular changes in Huntington's disease.

New insights into the elucidation of angiotensin-(1-7) in vivo antiarrhythmic effects and its related cellular mechanisms.

NEW FINDINGS: What is the central question of this study? Recently, there have been many studies exploring the biological effects of angiotensin-(1-7), which has been proved to have cardioprotective actions. However, the effects of this peptide on cardiac arrhythmias in vivo and details regarding its mechanism of action are still undetermined. What is the main finding and its importance? We investigated protective effects of angiotensin-(1-7) on cardiac arrhythmias in vivo, which were not properly explored in terms of cellular mechanisms. To verify effects of angiotensin-(1-7), we used different but complementary experimental approaches. Our data provide new evidence on the cellular mechanism and an in vivo demonstration of the acute antiarrhythmic effect of angiotensin-(1-7). Angiotensin-(1-7) [Ang-(1-7)] has been proved to have cardioprotective effects. However, the effects of this peptide on cardiac arrhythmias in vivo and details regarding its mechanism of action are still undetermined. The aim of this study was to investigate the protective effects of Ang-(1-7) against cardiac arrhythmias, its in vivo effects and cellular mechanism of action. We analysed the ECG upon inducement of arrhythmias in vivo in rats using a combination of halothane and adrenaline. To analyse the effects of Ang-(1-7) on cells, fresh mouse ventricular cardiomyocytes were isolated. The cardiomyocytes were superfused with a solution containing halothane and isoprenaline as a model to induce arrhythmias and used in three different approaches, namely a contractility assay, patch-clamp technique and confocal microscopy. The in vivo ECG showed that the injection of Ang-(1-7) (4 nm i.v.) significantly reduced cardiac arrhythmias [before, 49 ± 43 arrhythmic events versus after Ang-(1-7), 16 ± 14 arrhythmic events]. This effect was blocked by injection of A-779 and l-NAME, without changes in haemodynamic parameters. In addition, contractility experiments showed that Ang-(1-7) significantly decreased the number of arrhythmic events without changing the fractional shortening. This protection was associated with a reduction of the action potential repolarization and membrane hyperpolarization. Moreover, Ang-(1-7) decreased the number of calcium waves without any changes in the amplitude of the calcium transient, despite a significant reduction in the decay rate. Our data provide new evidence on the cellular mechanism together with an in vivo demonstration of the antiarrhythmic effects of Ang-(1-7).