In vivo tebuconazole administration impairs heart electrical function and facilitates the occurrence of dobutamine-induced arrhythmias: involvement of reactive oxygen species

Tebuconazole (TEB), a widely used pesticide in agriculture to combat fungal infections, is commonly detected in global food, potable water, groundwater, and human urine samples. Despite its known in vivo toxicity, its impact on heart function remains unclear. In a 28-day study on male Wistar rats (approximately 100 g), administering 10 mg/kg/day TEB or a vehicle (control) revealed no effect on body weight gain or heart weight, but an increase in the infarct area in TEB-treated animals. Notably, TEB induced time-dependent changes in in vivo electrocardiograms, particularly prolonging the QT interval after 28 days of administration. Isolated left ventricular cardiomyocytes exposed to TEB exhibited lengthened action potentials and reduced transient outward potassium current. TEB also increased reactive oxygen species (ROS) production in these cardiomyocytes, a phenomenon reversed by N-acetylcysteine (NAC). Furthermore, TEB-treated animals, when subjected to an in vivo dobutamine (Dob) and caffeine (Caf) challenge, displayed heightened susceptibility to severe arrhythmias, a phenotype prevented by NAC. In conclusion, TEB at the no observed adverse effect level (NOAEL) dose adversely affects heart electrical function, increases arrhythmic susceptibility, partially through ROS overproduction, and this phenotype is reversible by scavenging ROS with NAC.

Extracellular acidification reveals the antiarrhythmic properties of amiodarone related to late sodium current-induced atrial arrhythmia

BACKGROUND

Amiodarone (AMIO) is an antiarrhythmic drug with the pKa in the physiological range. Here, we explored how mild extracellular pH (pHe) changes shape the interaction of AMIO with atrial tissue and impact its pharmacological properties in the classical model of sea anemone sodium channel neurotoxin type 2 (ATX) induced late sodium current (INa-Late) and arrhythmias.

METHOD

Isolated atrial cardiomyocytes from male Wistar rats and human embryonic kidney cells expressing SCN5A Na+ channels were used for patch-clamp experiments. Isolated right atria (RA) and left atria (LA) tissue were used for bath organ experiments.

RESULTS

A more acidophilic pHe caused negative inotropic effects on isolated RA and LA atrial tissue, without modification of the pharmacological properties of AMIO. A pHe of 7.0 changed the sodium current (INa) related components of the action potential (AP), which was enhanced in the presence of AMIO. ATXinduced arrhythmias in isolated RA and LA. Also, ATX prolonged the AP duration and enhanced repolarization dispersion in isolated cardiomyocytes in both pHe 7.4 and pHe 7.0. Pre-incubation of the isolated RA and LA and isolated atrial cardiomyocytes with AMIO prevented arrhythmias induced by ATX only at a pHe of 7.0. Moreover, AMIO was able to block INa-Late induced by ATX only at a pHe of 7.0.

CONCLUSION

The pharmacological properties of AMIO concerning healthy rat atrial tissue are not dependent on pHe. However, the prevention of arrhythmias induced by INa-Late is pHe-dependent. The development of drugs analogous to AMIO with charge stabilization may help to create more effective drugs to treat arrhythmias related to the INa-Late.

Interaction of the antiarrhythmic drug Amiodarone with the sodium channel Nav1.5 depends on the extracellular pH

INTRODUCTION

Amiodarone (AMD) is a clinically used drug to treat arrhythmias with significant effect upon the cardiac sodium channel Nav1.5. AMD has a pKa of 6.56, and changes in extracellular pH (pHe) may alter its pharmacological properties. Here we explored how changes in pHe impacts the pharmacological properties of AMD upon human-Nav1.5-sodium-current (INa) and in ex vivo rat hearts.

METHODS

Embryonic-human-kidney-cells (HEK293) were used to transiently express the human alpha-subunit of NaV1.5 channels and the isolated heart of Wistar rats were used. Patch-Clamp technique was deployed to study INa and for electrocardiogram (ECG) evaluation the ex vivo heart preparation in the Langendorff system was applied.

RESULTS

The potency of AMD upon peak INa was ∼25x higher in pHe 7.0 when compared to pHe 7.4. Voltage dependence for activation did not differ among all groups. AMD shifted the steady-state inactivation curve to more hyperpolarized potentials, with similar magnitudes for both pHes. The recovery from INa inactivation was delayed in the presence of AMD with similar profile in both pHes. Interestingly, the use-dependent properties of AMD was distinct at pHe 7.0 and 7.4. Finally, AMD was able to change the ex vivo ECG profile, however at pHe 7.0+AMD a larger increase in the RR and QRS duration and in the QT interval when compared to pHe 7.4 was found.

CONCLUSIONS

The pharmacological properties of AMD upon NaV1.5 and isolated heart preparation depends on the pHe and its use in vivo during extracellular acidosis may cause a distinct biological response in the heart tissue.

Exploring the involvement of TASK-1 in the control of isolated rat right atrium function from healthy animals and an experimental model of monocrotaline-induced pulmonary hypertension

The TASK-1 channel belongs to the two-pore domain potassium channel family. It is expressed in several cells of the heart, including the right atrial (RA) cardiomyocytes and the sinus node, and TASK-1 channel has been implicated in the pathogenesis of atrial arrhythmias (AA). Thus, using the rat model of monocrotaline-induced pulmonary hypertension (MCT-PH), we explored the involvement of TASK-1 in AA. Four-week-old male Wistar rats were injected with 50 mg/kg of MCT to induce MCT-PH and isolated RA function was studied 14 days later. Additionally, isolated RA from six-week-old male Wistar rats were used to explore the ability of ML365, a selective blocker of TASK-1, to modulate RA function. The hearts developed right atrial and ventricular hypertrophy, inflammatory infiltrate and the surface ECG demonstrated increased P wave duration and QT interval, which are markers of MCT-PH. The isolated RA from the MCT animals showed enhanced chronotropism, faster contraction and relaxation kinetics, and a higher sensibility to extracellular acidification. However, the addition of ML365 to extracellular media was not able to restore the phenotype. Using a burst pacing protocol, the RA from MCT animals were more susceptible to develop AA, and simultaneous administration of carbachol and ML365 enhanced AA, suggesting the involvement of TASK-1 in AA induced by MCT. TASK-1 does not play a key role in the chronotropism and inotropism of healthy and diseased RA; however, it may play a role in AA in the MCT-PH model.

Naringin improves post-ischemic myocardial injury by activation of KATP channels

Naringin (NRG) is a flavonoid with recognized cardioprotective effects. Then, it was investigated the cardioprotective mechanisms of NRG against ischemia-reperfusion (I/R) injury. The rats were pretreated for 7 days (v.o.) with NRG (25 mg/kg) or n-acetylcysteine (NAC, 100 mg/kg) and their isolated hearts were subjected to global ischemia (30 min) and reperfusion (60 min). Furthermore, isolated hearts were perfused with 5 μM NRG in the presence of 10 μM glibenclamide (GLI) and subjected to I/R protocol. In healthy ventricular cardiomyocyte, it was evaluated the acute effect of 5 μM NRG on the GLI sensitive current. The results showed that NRG pretreatment restored the cardiac function and electrocardiogram (ECG) alterations induced by I/R injury, decreasing arrhythmia scores and the occurrence of severe arrhythmias. Lactate dehydrogenase and infarct area were decreased while superoxide dismutase (SOD), catalase and citrate synthase activities increased. Expression of SOD CuZn and SOD Mn not was altered. NRG treatment decreased reactive oxygen species (ROS) generation and lipid peroxidation without alter sulfhydryl groups and protein carbonylation. Also, NRG (5 μM) increased the glibenclamide sensitive current in isolated cardiomyocytes. In isolated heart, the cardioprotection of NRG was significantly reduced by GLI. Furthermore, NRG promoted downregulation of Bax expression and Bax/Bcl-2. Histopathological analysis showed that NRG decreased cell edema, cardiomyocytes and nucleus diameter. Thus, NRG has a cardioprotective effect against cardiac I/R injury which is mediated by its antioxidant and antiapoptotic actions and KATP channels activation.

Eugenol delays the onset of ouabain-induced ventricular cardiac arrhythmias in guinea pigs

Eugenol is an aromatic compound used in the manufacture of medicines, perfumes, cosmetics and as an anaesthetic due to the ability of the drug to block the neuronal isoform of voltage-gated Na+ channels (NaV ). Some arrhythmias are associated with gain of function in the sodium current (INa ) found in cardiomyocytes, and antiarrhythmic sodium channel blockers are commonly used in the clinical practice. This study sought to elucidate the potential mechanisms of eugenol's protection in the arrhythmic model of ouabain-induced arrhythmias in guinea pig heart. Ex vivo arrhythmias were induced using 50 μM of ouabain. The antiarrhythmic properties of eugenol were evaluated in the ex vivo heart preparation and isolated ventricular cardiomyocytes. The compound's effects on cardiac sodium current and action potential using the patch-clamp technique were evaluated. In all, eugenol decreased the ex vivo cardiac arrhythmias induced by ouabain. Furthermore, eugenol showed concentration dependent effect upon peak INa , left-shifted the stationary inactivation curve and delayed the recovery from inactivation of the INa . All these aspects are considered to be antiarrhythmic. Our findings demonstrate that eugenol has antiarrhythmic activity, which may be partially explained by the ability of eugenol to change de biophysical properties of INa of cardiomyocytes.

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.

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 β-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.

Isolated Left Atrium Morphofunctional Study of an Experimental Pulmonary Hypertension Model in Rats

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.

d-Limonene complexed with cyclodextrin attenuates cardiac arrhythmias in an experimental model of doxorubicin-induced cardiotoxicity: Possible involvement of calcium/calmodulin-dependent protein kinase type II

BACKGROUND

Arrhythmias are one manifestation of the cardiotoxicity that results from doxorubicin (Doxo) administration. Although cardiotoxicity is an anticipated outcome in anticancer therapies, there is still a lack of treatment options available for its effective management. This study sought to evaluate the possible cardioprotective effect of complex d-limonene (DL) plus hydroxypropyl-β-cyclodextrin (HβDL) during treatment with Doxo, focusing on the arrhythmic feature.

METHODS

Cardiotoxicity was induced in Swiss mice with Doxo 20 mg/kg, with 10 mg/kg of HβDL being administered 30 min before the Doxo. Plasma CK-MB and LDH levels were analyzed. Cellular excitability and susceptibility to cardiac and cardiomyocyte arrhythmias were evaluated using in vivo (pharmacological cardiac stress) and in vitro (burst pacing) ECG protocols. Ca2+ dynamics were also investigated. The expression of CaMKII and its activation by phosphorylation and oxidation were evaluated by western blot, and molecular docking was used to analyze the possible interaction between DL and CaMKII.

RESULTS

Electrocardiograms showed that administration of 10 mg/kg of HβDL prevented Doxo-induced widening of the QRS complex and QT interval. HβDL also prevented cardiomyocyte electrophysiological changes that trigger cellular arrhythmias, such as increases in action potential duration and variability; decreased the occurrence of delayed afterdepolarizations (DADs) and triggered activities (TAs), and reduced the incidence of arrhythmia in vivo. Ca2+ waves and CaMKII overactivation caused by phosphorylation and oxidation were also decreased. In the in silico study, DL showed potential inhibitory interaction with CaMKII.

CONCLUSION

Our results show that 10 mg/kg of βDL protects the heart against Doxo-induced cardiotoxicity arrhythmias, and that this is probably due to its inhibitory effect on CaMKII hyperactivation.

The effects of flavonoids in experimental sepsis: A systematic review and meta-analysis

Sepsis is a host's dysregulated immune response to an infection associated with systemic inflammation and excessive oxidative stress, which can cause multiple organ failure and death. The literature suggests that flavonoids, a broad class of secondary plant metabolites, have numerous biological activities which can be valuable in the treatment of sepsis. This study aimed to review the effects of flavonoids on experimental sepsis, focusing mainly on survival rate, and also summarizing information on its mechanisms of action. We searched in the main databases up to November 2022 using relevant keywords, and data were extracted and analyzed qualitatively and quantitatively. Thirty-two articles met the study criteria for review and 29 for meta-analysis. Overall, 30 different flavonoids were used in the studies. The flavonoids were able to strongly inhibit inflammatory response by reducing the levels of important pro-inflammatory mediators, for example, tumor necrosis factor-alpha and interleukin-1β, oxidative stress, and showed antibacterial and anti-apoptotic actions. The meta-analysis found an increase of 50% in survival rate of the animals treated with flavonoids. They appear to act as multi-target drugs and may be an excellent therapeutic alternative to reduce a number of the complications caused by sepsis, and consequently, to improve survival rate.

Ranolazine exerts atrial antiarrhythmic effects in a rat model of monocrotaline-induced pulmonary hypertension

Atrial arrhythmias are a hallmark of heart diseases. The antiarrhythmic drug ranolazine with multichannel blocker properties is a promising agent to treat atrial arrhythmias. We therefore used the rat model of monocrotaline-induced pulmonary-hypertension to assess whether ranolazine can reduce the incidence of ex vivo atrial arrhythmias in isolated right atrium. Four-week-old Wistar rats were injected with 50 mg/kg of monocrotaline, and isolated right atrium function was studied 14 days later. The heart developed right atrium and right ventricular hypertrophy, and the ECG showed an increased P wave duration and QT interval, which are markers of the disease. Moreover, monocrotaline injection caused enhanced chronotropism and faster kinetics of contraction and relaxation in isolated right atrium. Additionally, in a concentration-dependent manner, ranolazine showed chronotropic and ionotropic effects upon isolated right atrium, with higher potency in the control when compared with experimental model. Using a burst pacing protocol, the isolated right atrium from the monocrotaline-treated animals was more susceptible to develop arrhythmias, and ranolazine was able to attenuate the phenotype. Thus, we concluded that the rat model of monocrotaline-induced pulmonary-hypertension develops right atrium remodelling, which increased the susceptibility to present ex vivo atrial arrhythmias, and the antiarrhythmic drug ranolazine ameliorated the phenotype.

S-limonene protects the heart in an experimental model of myocardial infarction induced by isoproterenol: Possible involvement of mitochondrial reactive oxygen species

BACKGROUND

Myocardial infarction (MI) is associated with high mortality rates, despite the fact that there are therapies available. Importantly, excessive oxidative stress may contribute to ischemia/reperfusion injury leading to death related to MI. In this scenario, naturally occurring antioxidant compounds are an important source of possible therapeutic intervention. Thus, this study sought to elucidate the mechanisms of cardioprotection of s-limonene in an isoproterenol-induced MI animal model.

METHODS

Wistar rats were treated with 1 mg/kg s-limonene (SL) or 100 mg/kg N-acetylcysteine (NAC, positive control) once, 30 min after isoproterenol-induced MI (applied in two doses with a 24 h interval). The protective effects of SL in the heart were examined via the serum level of creatine kinase myocardial band (CK-MB), electrocardiographic profile, infarct size and histological parameters. Using isolated cardiomyocytes, we also assessed calcium transient amplitude, cytosolic and mitochondrial oxidative stress and the expression of proteins related to oxidative stress.

RESULTS

SL at a concentration of 1 mg/kg attenuated isoproterenol-induced MI injury, by preventing ST-segment elevation and QTc prolongation in the ECG. SL reduced the infarct size and collagen content in cardiac tissue. At the cellular level, SL prevented increased Ca²⁺, associated with attenuation of cytosolic and mitochondrial oxidative stress. These changes resulted in a reduction of the oxidized form of Ca²⁺ Calmodulin-Dependent Kinase II (CaMKII) and restored superoxide dismutase and glutathione peroxidase activity.

CONCLUSION

Our data show that s-limonene promotes cardioprotection against MI injury, probably through inhibition of increased Ca²⁺ and attenuation of oxidative stress via CaMKII.

Impact of IFN-γ Deficiency on the Cardiomyocyte Function in the First Stage of Experimental Chagas Disease

Chagas disease (CD) is caused by the parasitic protozoan T. cruzi. The progression of CD in ~30% of patients results in Chagasic Cardiomyopathy (CCM). Currently, it is known that the inflammatory system plays a significant role in the CCM. Interferon-gamma (IFN-γ) is the major cytokine involved in parasitemia control but has also been linked to CCM. The L-type calcium current (I_Ca,L) is crucial in the excitation/contraction coupling in cardiomyocytes. Thus, we compared I_Ca,L and the mechanical properties of cardiomyocytes isolated from infected wild type (WT) and IFN-γ^(−/−) mice in the first stage of T. cruzi infection. Using the patch clamp technique, we demonstrated that the infection attenuated I_Ca,L in isolated cardiomyocytes from the right and left ventricles of WT mice at 15 days post-infection (dpi), which was not observed in the IFN-γ^(−/−) cardiomyocytes. However, I_Ca,L was attenuated between 26 and 30 dpi in both experimental groups. Interestingly, the same profile was observed in the context of the mechanical properties of isolated cardiomyocytes from both experimental groups. Simultaneously, we tracked the mortality and MCP-1, TNF-α, IL-12, IL-6, and IL-10 serum levels in the infected groups. Importantly, the IFN-γ^(−/−) and WT mice presented similar parasitemia and serum inflammatory markers at 10 dpi, indicating that the modifications in the cardiomyocyte functions observed at 15 dpi were directly associated with IFN-γ^(−/−) deficiency. Thus, we showed that IFN-γ plays a crucial role in the electromechanical remodeling of cardiomyocytes during experimental T. cruzi infection in mice.

Inhibition of calcium/calmodulin (Ca2+ /CaM)-Calcium/calmodulin-dependent protein kinase II (CaMKII) axis reduces in vitro and ex vivo arrhythmias in experimental Chagas disease

Chagasic cardiomyopathy (CCC) is one of the main causes of heart failure and sudden death in Latin America. To date, there is no available medication to prevent or reverse the onset of cardiac symptoms. CCC occurs in a scenario of disrupted calcium dynamics and enhanced oxidative stress, which combined, may favor the hyper activation of calcium/calmodulin (Ca²⁺ /CaM)-calcium/calmodulin-dependent protein kinase II (CaMKII) (Ca²⁺ /CaM-CaMKII) pathway, which is fundamental for heart physiology and it is implicated in other cardiac diseases. Here, we evaluated the association between Ca²⁺ /CaM-CaMKII in the electro-mechanical (dys)function of the heart in the early stage of chronic experimental Trypanosoma cruzi infection. We observed that in vitro and ex vivo inhibition of Ca²⁺ /CaM-CaMKII reversed the arrhythmic profile of isolated hearts and isolated left-ventricles cardiomyocytes. The benefits of the limited Ca²⁺ /CaM-CaMKII activation to cardiomyocytes' electrical properties are partially related to the restoration of Ca²⁺ dynamics in a damaged cellular environment created after T. cruzi infection. Moreover, Ca²⁺ /CaM-CaMKII inhibition prevented the onset of arrhythmic contractions on isolated heart preparations of chagasic mice and restored the responsiveness to the increase in the left-ventricle pre-load. Taken together, our data provide the first experimental evidence for the potential of targeting Ca²⁺ /CaM-CaMKII pathway as a novel therapeutic target to treat CCC.

SCN5A compound heterozygosity mutation in Brugada syndrome: Functional consequences and the implication for pharmacological treatment

AIMS

SCN5A gene encodes the α-subunit of Na_v1.5, mainly found in the human heart. SCN5A variants are the most common genetic alterations associated with Brugada syndrome (BrS). In rare cases, compound heterozygosity is observed; however, its functional consequences are poorly understood. We aimed to analyze the functional impact of de novo Na_v1.5 mutations in compound heterozygosity in distinct alleles (G400R and T1461S positions) previously found in a patient with BrS. Moreover, we evaluated the potential benefits of quinidine to improve the phenotype of mutant Na⁺ channels in vitro.

MATERIALS AND METHODS

The functional properties of human wild-type and Na_v1.5 variants were evaluated using whole-cell patch-clamp and immunofluorescence techniques in transiently expressed human embryonic kidney (HEK293) cells.

KEY FINDINGS

Both variants occur in the highly conservative positions of SCN5A. Although all variants were expressed in the cell membrane, a significant reduction in the Na⁺ current density (except for G400R alone, which was undetected) was observed along with abnormal biophysical properties, once the variants were expressed in homozygosis and heterozygosis. Interestingly, the incubation of transfected cells with quinidine partially rescued the biophysical properties of the mutant Na⁺ channel.

SIGNIFICANCE

De novo compound heterozygosis mutations in SNC5A disrupt the Na⁺ macroscopic current. Quinidine could partially reverse the in vitro loss-of-function phenotype of Na⁺ current. Thus, our data provide, for the first time, a detailed biophysical characterization of dysfunctional Na⁺ channels linked to compound heterozygosity in BrS as well as the benefits of the pharmacological treatment using quinidine on the biophysical properties of Na_v1.5.

Andrographolide protects against isoproterenol-induced myocardial infarction in rats through inhibition of L-type Ca2+ and increase of cardiac transient outward K+ currents

Myocardial infarction (MI) is the irreversible injury of the myocardium caused by prolonged myocardial ischemia and is a major cause of heart failure and eventual death among ischemic patients. The present study assessed the protective potentials of andrographolide against isoproterenol-induced myocardial infarction in rats. Animals were randomly divided into four groups: Control (Ctr) group received 0.9% saline solution once daily for 21 days, Isoproterenol (Iso) group received 0.9% saline solution once daily for 19 days followed by 80 mg/kg/day of isoproterenol hydrochloride solution on day 20 and 21, Andrographolide (Andro) group received 20 mg/kg/day of andrographolide for 21 days, and Andrographolide plus Isoproterenol (Andro + Iso) group received 20 mg/kg/day of andrographolide for 21 days with co-administration of 80 mg/kg/day of isoproterenol hydrochloride solution on day 20 and 21. After all treatments, cardiac-specific parameters that define cardiac health and early subacute MI were measured in all groups using both biophysical and pharmacological assay methods. Isoproterenol administration significantly (P < 0.05) increased cardiac mass indexes, systemic cardiac biomarkers, infarct size and caused cardiac histological alterations; significantly (P < 0.05) increased heart rate, QRS & QTc intervals and caused ST-segment elevation; significantly (P < 0.05) increased myocytes shortening, action potential duration (APD), L-type Ca²⁺ current (I_Ca,L) density and significantly (P < 0.05) decreased transient outward K⁺ current (I_to) density typical of the early subacute MI. Interestingly, pretreatment with andrographolide prevented and or minimized these anomalies, notably, by reducing I_Ca,L density and increasing I_to density significantly. Therefore, andrographolide could be seen as a promising therapeutic agent capable of making the heart resistant to early subacute infarction and it could be used as template for the development of semisynthetic drug(s) for cardiac protection against MI.

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

Na_v1.5-derived Na⁺ current (I_Na) exerts a pivotal role in the depolarization phase of cardiomyocytes' action potential, and, therefore, changes in I_Na can contribute to fatal arrhythmias. Na_v1.5 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 Na_v1.5 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 Na_v1.5 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 Na_v1.5, 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 Na_v1.5. Important, amiodarone efficacy is variable among patients. Here we show that ethnicity-related SCN5A polymorphisms lead to altered Na_v1.5-amiodarone interaction, which may be the cause for the variable efficacy observed in clinical usage of amiodarone.

Cardiodepressive Effect of Eugenyl Acetate in Rodent Heart

No presente trabalho investigou-se o efeito inotrópico do acetato de eugenil (AE), bem como sua ação sobre a corrente de Ca²⁺ do tipo L (I_Ca,L). Os experimentos de contratilidade foram realizados em átrio esquerdo isolado de cobaia exposto às concentrações crescentes da droga (1 a 5.000μM). O AE reduziu a força de contração atrial (IC₅₀=558±24,06μM) de modo dependente de concentração. O efeito do AE sobre a I_Ca,L também foi avaliado em cardiomiócitos ventriculares isolados de camundongos, utilizando-se a técnica de “patch-clamp”. O AE apresentou um efeito inibitório (IC₅₀=1.337±221μM) sobre os canais de Ca²⁺ sensíveis à voltagem (Ca_V1.2). Em conclusão, o AE apesenta efeito cardiodepressor que se deve, pelo menos em parte, à diminuição da entrada de Ca²⁺ nos cardiomiócitos.

Impact of pacing frequency in amiodarone interaction with cardiomyocytes near physiological temperature in health and disease conditions

Long QT syndrome type 3 (LQT-3) is a disease related to abnormal cardiac sodium channel function (Nav 1.5), usually due to augmented late sodium current (I_NaL ), and may lead to ventricular fibrillation. Amiodarone is approved for ventricular fibrillation. Thus, we investigated whether pacing frequency impacts the ability of amiodarone to reverse the arrhythmic phenotype observed in LQT-3. Anemone neurotoxin 2 (ATX-II, here named only ATX) was used to enhance I_NaL in mice left ventricular myocytes (LVM). A video detector system monitored sarcomere shortening. At 1 Hz, amiodarone attenuated sarcomere shortening only at 10 µmol/L; at 3 and 5 Hz, 0.1 and 1 µmol/L amiodarone also reduced sarcomere shortening. However, no effect of amiodarone was observed on time to 50% of sarcomere contraction and relaxation. In LVM exposed to ATX (10 nmol/L), an arrhythmic phenotype was observed, and it was more severe when cells were paced at 1 Hz. Amiodarone failed to reverse the ATX induced phenotype at different pacing frequencies. Thus, our results suggest that amiodarone's ability to reverse arrhythmias induced by augmentation of I_NaL is limited. These findings suggest further experimentation will be required to clarify whether a clinical effect can be ascribed to an effect of amiodarone on other ion channels in LQT-3.

NOTCH1 is critical for fibroblast-mediated induction of cardiomyocyte specialization into ventricular conduction system-like cells in vitro

Cardiac fibroblasts are present throughout the myocardium and are enriched in the microenvironment surrounding the ventricular conduction system (VCS). Several forms of arrhythmias are linked to VCS abnormalities, but it is still unclear whether VCS malformations are cardiomyocyte autonomous or could be linked to crosstalk between different cell types. We reasoned that fibroblasts influence cardiomyocyte specialization in VCS cells. We developed 2D and 3D culture models of neonatal rat cardiac cells to assess the influence of cardiac fibroblasts on cardiomyocytes. Cardiomyocytes adjacent to cardiac fibroblasts showed a two-fold increase in expression of VCS markers (NAV1.5 and CONTACTIN 2) and calcium transient duration, displaying a Purkinje-like profile. Fibroblast-conditioned media (fCM) was sufficient to activate VCS-related genes (Irx3, Scn5a, Connexin 40) and to induce action potential prolongation, a hallmark of Purkinge phenotype. fCM-mediated response seemed to be spatially-dependent as cardiomyocyte organoids treated with fCM had increased expression of connexin 40 and NAV1.5 primarily on its outer surface. Finally, NOTCH1 activation in both cardiomyocytes and fibroblasts was required for connexin 40 up-regulation (a proxy of VCS phenotype). Altogether, we provide evidence that cardiac fibroblasts influence cardiomyocyte specialization into VCS-like cells via NOTCH1 signaling in vitro.

Effects of amiodarone on rodent ventricular cardiomyocytes: Novel perspectives from a cellular model of Long QT Syndrome Type 3

AIMS

Amiodarone (AMIO) is currently used in medical practice to reverse ventricular tachycardia. Here we determine the effects of AMIO in the electromechanical properties of isolated left ventricle myocyte (LVM) from mice and guinea pig and in a cellular model of Long QT Syndrome Type 3 (LQTS-3) using anemone neurotoxin 2 (ATX II), which induces increase of late sodium current in LVM.

MAIN METHODS AND KEY FINDINGS

Using patch-clamp technique, fluorescence imaging to detect cellular Ca²⁺ transient and sarcomere detection systems we evaluate the effect of AMIO in healthy LVM. AMIO produced a significant reduction in the percentage of sarcomere shortening (0.1, 1 and 10 μM) in a range of pacing frequencies, however, without significant attenuation of Ca²⁺ transient. Also, 10 μM of AMIO caused the opposite effect on action potential repolarization of mouse and guinea pig LVM. When LVM from mouse and guinea pig were paced in a range of pacing frequencies and exposed to ATX (10 nM), AMIO (10 μM) was only able to abrogate electromechanical arrhythmias in LVM from guinea pig at lower pacing frequency.

SIGNIFICANCE

AMIO has negative inotropic effect with opposite effect on action potential waveform in mouse and guinea pig LVM. Furthermore, the antiarrhythmic action of AMIO in LQTS-3 is species and frequency-dependent, which indicates that AMIO may be beneficial for some types of arrhythmias related to late sodium current.

Time Course of Gene Expression Profile in Renal Ischemia and Reperfusion Injury in Mice

Ischemic renal failure is an inflammatory disease that can affect various organs, including the heart. The organ responds to the stimulus and undergoes tissue remodeling that can result in cardiac hypertrophy. This study aimed to characterize the cardiac global gene expression profile in renal ischemia/reperfusion (IR) model using microarray technology. To do that, left kidney ischemia was induced in male C57BL/6 mice for 60 minutes, followed by reperfusion (IR) for 5, 8, 15, or 20 days post ischemia (dpi). Total cardiac tissue RNA was extracted and hybridized to chips with 35,000 mouse genes. The GeneChip Mouse Genome 430 2.0 Array Expression chip (Affymetrix) was used, and CEL files generated were processed with DNA-Chip-Analyzer (dCHIP) software. Subsequent analysis considered only differences among groups of at least 1.2-fold (up or down) expression changes. Analyses of the samples indicated positive modulation of 17,413 genes and 405 pathways and negative modulation of 18,287 genes and 300 pathways. A narrower analysis of genes related to inflammation, metabolism, apoptosis, oxidative stress, and channels/ion transport was performance, and it was correlated with IR injury, corroborating previous data from literature. Renal IR induced a global shift in cardiac tissue gene expression; in particular, genes related to the inflammatory system and cardiomyocyte function were changed. The in-depth study of the cell signaling in the present study could stimulate the development of new therapeutic option to ameliorate the outcome of renal-IR-induced heart damage.

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.

Functional Upregulation of STIM-1/Orai-1-Mediated Store-Operated Ca2+ Contributing to the Hypertension Development Elicited by Chronic EtOH Consumption

BACKGROUND

Chronic ethanol (EtOH) consumption has been associated with deleterious effects on the cardiovascular system by abnormal calcium (Ca2+) handling. Store-operated Ca2+ entry (SOCE) is related to cardiovascular remodeling which leads to the hypertension development, and the coupling between STIM-1 (ER Ca2+ sensor) and Orai-1 (channel pore) is a key mechanism to control SOCE through of store-operated Ca2+ channels (SOCCs). However, the role of STIM-1/Orai-1-mediated SOCE and its cross-talk with EtOH-triggered vascular remodeling and hypertension remain poorly understood. We address this subject in the present study by evaluating how chronic EtOH consumption induces alterations in Ca2+ handling via SOCE.

METHODS

Male Wistar Kyoto (WKY) and Spontaneously Hypertensive (SHR) rats were subjected to the intake of increasing EtOH concentrations (5-20%, for 30 days). Systolic blood pressure (SBP) and EtOH concentration were measured; cardiovascular remodeling was assessed by histomorphometry; and function/ expression of STIM-1/Orai-1-mediated Ca2+ influx were evaluated by isometric contraction and western blot experiments.

RESULTS

Compared to the WKY-Control, our results show that: (1) chronic EtOH consumption caused a significant elevation of SBP in both strains; (2) cardiac hypertrophy and hypertrophic aortic wall remodeling much more pronounced in WKY-EtOH; (3) decreased capacity of ER to store and release Ca2+; (4) increased STIM-1/Orai-1-mediated SOCCs activation, which was selectively inhibited by YM-58483; and (5) increased expression of STIM-1 in WKY-EtOH and SHR-Control rats.

CONCLUSION

These findings suggest that hypertrophic aortic remodeling and abnormal contraction triggered mainly by Ca2+ overload via STIM-1/Orai-1-mediated SOCE through SOCCs are involved hypertension developed by EtOH consumption.

Exercise Training Protects Cardiomyocytes from Deleterious Effects of Palmitate

We investigated the effects of palmitate, a high saturated fat, on Ca²⁺, action potential and reactive oxygen species dynamics in cardiomyocytes from untrained and trained mice. Male mice were subjected to moderate intensity exercise training on a treadmill. Cardiomyocytes of untrained and trained mice were isolated, treated for 30 min with palmitate and intracellular calcium transient and action potential duration were recorded. Additionally, we assessed reactive oxygen species generation. Treatment of cardiomyocytes from untrained mice with palmitate induced a significant decrease in Ca²⁺ transient magnitude by 34%. Exercise training did not change cardiomyocyte Ca²⁺ dynamics in the control group. However, trained cardiomyocytes were protected from deleterious effects of palmitate. Action potential duration was not altered by palmitate in either untrained or trained cardiomyocytes. Moreover, palmitate treatment increased reactive oxygen species generation in both untrained and trained cardiomyocytes. Nevertheless, the levels of reactive oxygen species in trained cardiomyocytes treated with palmitate were still 27% lower than those seen at basal conditions in untrained cardiomyocytes. Taken together, these findings indicate that exercise training protects cardiomyocytes from deleterious effects of palmitate possibly by inhibiting exacerbated ROS production.

The Impact of Heterozygous KCNK3 Mutations Associated With Pulmonary Arterial Hypertension on Channel Function and Pharmacological Recovery

BACKGROUND

Heterozygous loss of function mutations in the KCNK3 gene cause hereditary pulmonary arterial hypertension (PAH). KCNK3 encodes an acid-sensitive potassium channel, which contributes to the resting potential of human pulmonary artery smooth muscle cells. KCNK3 is widely expressed in the body, and dimerizes with other KCNK3 subunits, or the closely related, acid-sensitive KCNK9 channel.

METHODS AND RESULTS

We engineered homomeric and heterodimeric mutant and nonmutant KCNK3 channels associated with PAH. Using whole-cell patch-clamp electrophysiology in human pulmonary artery smooth muscle and COS7 cell lines, we determined that homomeric and heterodimeric mutant channels in heterozygous KCNK3 conditions lead to mutation-specific severity of channel dysfunction. Both wildtype and mutant KCNK3 channels were activated by ONO-RS-082 (10 μmol/L), causing cell hyperpolarization. We observed robust gene expression of KCNK3 in healthy and familial PAH patient lungs, but no quantifiable expression of KCNK9, and demonstrated in functional studies that KCNK9 minimizes the impact of select KCNK3 mutations when the 2 channel subunits co-assemble.

CONCLUSIONS

Heterozygous KCNK3 mutations in PAH lead to variable loss of channel function via distinct mechanisms. Homomeric and heterodimeric mutant KCNK3 channels represent novel therapeutic substrates in PAH. Pharmacological and pH-dependent activation of wildtype and mutant KCNK3 channels in pulmonary artery smooth muscle cells leads to membrane hyperpolarization. Co-assembly of KCNK3 with KCNK9 subunits may provide protection against KCNK3 loss of function in tissues where both KCNK9 and KCNK3 are expressed, contributing to the lung-specific phenotype observed clinically in patients with PAH because of KCNK3 mutations.

(-)-Terpinen-4-ol changes intracellular Ca2+ handling and induces pacing disturbance in rat hearts

(-)-Terpinen-4-ol is a naturally occurring plant monoterpene and has been shown to have a plethora of biological activities. The objective of this study was to investigate the effects of (-)-terpinen-4-ol on the rat heart, a key player in the control and maintenance of arterial blood pressure. The effects of (-)-terpinen-4-ol on the rat heart were investigated using isolated left atrium isometric force measurements, in vivo electrocardiogram (ECG) recordings, patch clamp technique, and confocal microscopy. It was observed that (-)-terpinen-4-ol reduced contraction force in an isolated left atrium at millimolar concentrations. Conversely, it induced a positive inotropic effect and extrasystoles at micromolar concentrations, suggesting that (-)-terpinen-4-ol may have arrhythmogenic activity on cardiac tissue. In anaesthetized animals, (-)-terpinen-4-ol also elicited rhythm disturbance, such as supraventricular tachycardia and atrioventricular block. To investigate the cellular mechanism underlying the dual effect of (-)-terpinen-4-ol on heart muscle, experiments were performed on isolated ventricular cardiomyocytes to determine the effect of (-)-terpinen-4-ol on L-type Ca²⁺ currents, Ca²⁺ sparks, and Ca²⁺ transients. The arrhythmogenic activity of (-)-terpinen-4-ol in vitro and in vivo may be explained by its effect on intracellular Ca²⁺ handling. Taken together, our data suggest that (-)-terpinen-4-ol has cardiac arrhythmogenic activity.

Dissection of the Effects of Quercetin on Mouse Myocardium

Quercetin is a plant flavonoid with several biological activities. This study aimed to describe quercetin effects on contractile and electrophysiological properties of the cardiac muscle as well as on calcium handling. Quercetin elicited positive inotropism that was significantly reduced by propranolol indicating an involvement of the sympathetic nervous system. In cardiomyocytes, 30 μM quercetin increased I_Ca,L at 0 mV from -0.95 ± 0.01 A/F to -1.21 ± 0.08 A/F. The membrane potential at which 50% of the channels are activated (V_0.5 ) shifted towards more negative potentials from -13.06 ± 1.52 mV to -19.26 ± 1.72 mV and did not alter the slope factor. Furthermore, quercetin increased [Ca²⁺ ]_i transient by 28% when compared to control. Quercetin accelerated [Ca²⁺ ]_i transient decay time, which could be attributed to SERCA activation. In resting cardiomyocytes, quercetin did not change amplitude or frequency of Ca²⁺ sparks. In isolated heart, quercetin increased heart rate and decreased PRi, QTc and duration of the QRS complex. Thus, we showed that quercetin activates β-adrenoceptors, leading to increased L-type Ca²⁺ current and cell-wide intracellular Ca²⁺ transient without visible changes in Ca²⁺ sparks.

Absence of suppressor of cytokine signaling 2 turns cardiomyocytes unresponsive to LIF-dependent increases in Ca2+ levels

Little is known regarding the role of suppressor of cytokine signaling (SOCS) in the control of cytokine signaling in cardiomyocytes. We investigated the consequences of SOCS2 ablation for leukemia inhibitory factor (LIF)-induced enhancement of intracellular Ca²⁺ ([Ca²⁺]_i) transient by performing experiments with cardiomyocytes from SOCS2-knockout (ko) mice. Similar levels of SOCS3 transcripts were seen in cardiomyocytes from wild-type and SOCS2-ko mice, while SOCS1 mRNA was reduced in SOCS2-ko. Immunoprecipitation experiments showed increased SOCS3 association with gp130 receptor in SOCS2-ko myocytes. Measurements of Ca²⁺ in wild-type myocytes exposed to LIF showed a significant increase in the magnitude of the Ca²⁺ transient. This change was absent in LIF-treated SOCS2-ko cells. LIF activation of ERK and STAT3 was observed in both wild-type and SOCS2-ko cells, indicating that in SOCS2-ko, LIF receptors were functional, despite the lack of effect in the Ca²⁺ transient. In wild-type cells, LIF-induced increase in [Ca²⁺]_i and phospholamban Thr17 [PLN(Thr17)] phosphorylation was inhibited by KN-93, indicating a role for CaMKII in LIF-induced Ca²⁺ raise. LIF-induced phosphorylation of PLN(Thr17) was abrogated in SOCS2-ko myocytes. In wild-type cardiomyocytes, LIF treatment increased L-type Ca²⁺ current (I_Ca,L), a key activator of CaMKII in response to LIF. Conversely, SOCS2-ko myocytes failed to activate I_Ca,L in response to LIF, providing a rationale for the lack of LIF effect on Ca²⁺ transient. Our data show that absence of SOCS2 turns cardiomyocytes unresponsive to LIF-induced [Ca²⁺] raise, indicating that endogenous levels of SOCS2 are crucial for full activation of LIF signaling in the heart.

Cardiovascular effects of Sp-CTx, a cytolysin from the scorpionfish (Scorpaena plumieri) venom

Fish venom cytolysins are multifunctional proteins that in addition to their cytolytic/hemolytic effects display neurotoxic, cardiotoxic and inflammatory activities, being described as "protein lethal factors". A pore-forming cytolysin called Sp-CTx (Scorpaena plumieriCytolytic Toxin) has been recently purified from the venom of the scorpionfish Scorpaena plumieri. It is a glycoprotein with dimeric constitution, comprising subunits of approximately 65 kDa. Previous studies have revealed that this toxin has a vasorelaxant activity that appears to involve the L-arginine-nitric oxide synthase pathway; however its cardiovascular effects have not been fully comprehended. The present study examined the cardiovascular effects of Sp-CTx in vivo and in vitro. In anesthetized rats Sp-CTx (70 μg/kg i.v) produced a biphasic response which consisted of an initial systolic and diastolic pressure increase followed by a sustained decrease of these parameters and the heart rate. In isolated rats hearts Sp-CTx (10(-9) to 5 × 10(-6) M) produced concentration-dependent and transient ventricular positive inotropic effect and vasoconstriction response on coronary bed. In papillary muscle, Sp-CTx (10(-7) M) also produced an increase in contractile isometric force, which was attenuated by the catecholamine releasing agent tyramine (100 μM) and the β-adrenergic antagonist propranolol (10 μM). On isolated ventricular cardiomyocytes Sp-CTx (1 nM) increased the L-type Ca(2+) current density. The results show that Sp-CTx induces disorders in the cardiovascular system through increase of sarcolemmal calcium influx, which in turn is partially caused by the release of endogenous noradrenaline.

Altered Cardiomyocyte Function and Trypanosoma cruzi Persistence in Chagas Disease

Chagas disease, caused by the triatominae Trypanosoma cruzi, is one of the leading causes of heart malfunctioning in Latin America. The cardiac phenotype is observed in 20-30% of infected people 10-40 years after their primary infection. The cardiac complications during Chagas disease range from cardiac arrhythmias to heart failure, with important involvement of the right ventricle. Interestingly, no studies have evaluated the electrical properties of right ventricle myocytes during Chagas disease and correlated them to parasite persistence. Taking advantage of a murine model of Chagas disease, we studied the histological and electrical properties of right ventricle in acute (30 days postinfection [dpi]) and chronic phases (90 dpi) of infected mice with the Colombian strain of T. cruzi and their correlation to parasite persistence. We observed an increase in collagen deposition and inflammatory infiltrate at both 30 and 90 dpi. Furthermore, using reverse transcriptase polymerase chain reaction, we detected parasites at 90 dpi in right and left ventricles. In addition, we observed action potential prolongation and reduced transient outward K(+) current and L-type Ca(2+) current at 30 and 90 dpi. Taking together, our results demonstrate that T. cruzi infection leads to important modifications in electrical properties associated with inflammatory infiltrate and parasite persistence in mice right ventricle, suggesting a causal role between inflammation, parasite persistence, and altered cardiomyocyte function in Chagas disease. Thus, arrhythmias observed in Chagas disease may be partially related to altered electrical function in right ventricle.

Electrical properties of isolated cardiomyocytes in a rat model of thiamine deficiency

In modern society, thiamine deficiency (TD) remains an important medical condition linked to altered cardiac function. There have been contradictory reports about the impact of TD on heart physiology, especially in the context of cardiac excitability. In order to address this particular question, we used a TD rat model and patch-clamp technique to investigate the electrical properties of isolated cardiomyocytes from epicardium and endocardium. Neither cell type showed substantial differences on the action potential waveform and transient outward potassium current. Based on our results we can conclude that TD does not induce major electrical remodeling in isolated cardiac myocytes in either endocardium or epicardium cells.

Pharmacological evaluation of R(+)-pulegone on cardiac excitability: role of potassium current blockage and control of action potential waveform

INTRODUCTION

R(+)-pulegone is a ketone monoterpene and it is the main constituent of essential oils in several plants. Previous studies provided some evidence that R(+)-pulegone may act on isolated cardiac myocytes. In this study, we evaluated in extended detail, the pharmacological effects of R(+)-pulegone on cardiac tissue.

METHODS

Using in vivo measurements of rat cardiac electrocardiogram (ECG) and patch-clamp technique in isolated myocytes we determinate the influence of R(+)-pulegone on cardiac excitability.

RESULTS

R(+)-pulegone delayed action potential repolarization (APR) in a concentration-dependent manner (EC50=775.7±1.48, 325.0±1.30, 469.3±1.91 μM at 10, 50 and 90% of APR respectively). In line with prolongation of APR R(+)-pulegone, in a concentration-dependent manner, blocked distinct potassium current components (transient outward potassium current (I(to)), rapid delayed rectifier potassium current (I(Kr)), inactivating steady state potassium current (I(ss)) and inward rectifier potassium current (I(K1))) (EC50=1441±1.04; 605.0±1.22, 818.7±1.22; 1753±1.09 μM for I(to), I(Kr), I(ss) and I(K1), respectively). The inhibition occurred in a fast and reversible way, without changing the steady-state activation curve, but instead shifting to the left the steady-state inactivation curve (V1/2 from -56.92±0.35 to -67.52±0.19 mV). In vivo infusion of 100 mg/kg R(+)-pulegone prolonged the QTc (∼40%) and PR (∼62%) interval along with reducing the heart rate by ∼26%.

CONCLUSION

Taken together, R(+)-pulegone prolongs the APR by inhibiting several cardiomyocyte K(+) current components in a concentration-dependent manner. This occurs through a direct block by R(+)-pulegone of the channel pore, followed by a left shift on the steady state inactivation curve. Finally, R(+)-pulegone induced changes in some aspects of the ECG profile, which are in agreement with its effects on potassium channels of isolated cardiomyocytes.

Cardiomyocyte dysfunction during the chronic phase of Chagas disease

Chagas disease, which is caused by the parasite Trypanosoma cruzi, is an important cause of heart failure. We investigated modifications in the cellular electrophysiological and calcium-handling characteristics of an infected mouse heart during the chronic phase of the disease. The patch-clamp technique was used to record action potentials (APs) and L-type Ca2+ and transient outward K+ currents. [Ca2+]i changes were determined using confocal microscopy. Infected ventricular cells showed prolonged APs, reduced transient outward K+ and L-type Ca2+ currents and reduced Ca2+ release from the sarcoplasmic reticulum. Thus, the chronic phase of Chagas disease is characterised by cardiomyocyte dysfunction, which could lead to heart failure.

Current aspects of thiamine deficiency on heart function

Beriberi is a disease caused by thiamine deficiency (TD), which may lead to heart problems, including heart failure. Despite the fact that thiamine prevalence is reduced in the industrialized world, it remains a health hazard especially due to chronic alcohol consumption. Diagnosing the presence of TD based on both electrocardiogram and echocardiogram exams is particularly challenging because of its non-specific symptoms. TD diagnosis is unique, which then leads to determination of its severity. If thiamine infusion abrogates its symptomology, only then can the case be definitely diagnosed as TD. Another condition eliciting increased likelihood of developing TD in humans is furosemide administration to heart failure patients. Furosemide administration worsens heart failure due to heightened TD. However, literature data provided are contradictory and require clarification. Up until now, the rat has been the preferred TD animal model. However, the results are even more contradictory than those in humans. It seems that if the rat TD models are separated into two distinct groups, according to animal age, the results appear to be more consistent: younger rats are more prone to develop TD signs similar to those found in humans. Their symptoms stem from changes in cardiac myocyte function that are reversed after thiamine supplementation. However, it remains an open question as to why only younger rats are able to develop human-like symptoms and deserve further investigation.

A novel channelopathy in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension is a devastating disease with high mortality. Familial cases of pulmonary arterial hypertension are usually characterized by autosomal dominant transmission with reduced penetrance, and some familial cases have unknown genetic causes.

METHODS

We studied a family in which multiple members had pulmonary arterial hypertension without identifiable mutations in any of the genes known to be associated with the disease, including BMPR2, ALK1, ENG, SMAD9, and CAV1. Three family members were studied with whole-exome sequencing. Additional patients with familial or idiopathic pulmonary arterial hypertension were screened for the mutations in the gene that was identified on whole-exome sequencing. All variants were expressed in COS-7 cells, and channel function was studied by means of patch-clamp analysis.

RESULTS

We identified a novel heterozygous missense variant c.608 G→A (G203D) in KCNK3 (the gene encoding potassium channel subfamily K, member 3) as a disease-causing candidate gene in the family. Five additional heterozygous missense variants in KCNK3 were independently identified in 92 unrelated patients with familial pulmonary arterial hypertension and 230 patients with idiopathic pulmonary arterial hypertension. We used in silico bioinformatic tools to predict that all six novel variants would be damaging. Electrophysiological studies of the channel indicated that all these missense mutations resulted in loss of function, and the reduction in the potassium-channel current was remedied by the application of the phospholipase inhibitor ONO-RS-082.

CONCLUSIONS

Our study identified the association of a novel gene, KCNK3, with familial and idiopathic pulmonary arterial hypertension. Mutations in this gene produced reduced potassium-channel current, which was successfully remedied by pharmacologic manipulation. (Funded by the National Institutes of Health.)

The positive inotropic effect of the ethyl acetate fraction from Erythrina velutina leaves on the mammalian myocardium: the role of adrenergic receptors

Objectives

We studied the effects of ethyl acetate fraction (EAcF) obtained from Erythrina velutina leaves on mammalian myocardium.

Methods

The effect of EAcF on the contractility was studied using guinea-pig left atria mounted in a tissue bath (Tyrode's solution, 29°C, 95% CO2, 5% O2) and electrically stimulated (1 Hz). Concentration-response curves of EAcF were obtained in the presence of propranolol (1 μm), nifedipine (1 μm) and in reserpinized animals (5 mg/kg). The involvement of l-type calcium current (ICa,L) on the EAcF effect was observed in cardiomyocytes of mice assessed using patch-clamp technique.

Key findings

EAcF (550 μg/ml) had a positive inotropic effect, increasing the atrial force by 164% (EC50 = 157 ± 44 μg/ml, n = 6), but it was less potent than isoproterenol (EC50 = 0.0036 ± 0.0019 μg/ml, n = 8). The response evoked by EAcF was abolished by propranolol or nifedipine. Reserpine did not alter the inotropic response of EAcF. Furthermore, an enhancement of the ICa,L peak (31.2%) with EAcF was observed. Chemical analysis of EAcF revealed the presence of at least 10 different flavonoid glycoside derivatives. Two were identified as vicenin II and isorhoifolin.

Conclusions

We conclude that EAcF increases the cardiac contractile force by increasing the l-type calcium current and activating the adrenergic receptor pathway.

Cardiodepressive effect elicited by the essential oil of Alpinia speciosa is related to L-type Ca²+ current blockade

This study was undertaken to elucidate the effect of the essential oil from Alpinia speciosa (EOAs) on cardiac contractility and the underlying mechanisms. The essential oil was obtained from Alpinia speciosa leaves and flowers and the oil was analyzed by GC-MS method. Chemical analysis revealed the presence of at least 18 components. Terpinen-4-ol and 1,8-cineole corresponded to 38% and 18% of the crude oil, respectively. The experiments were conducted on spontaneously-beating right atria and on electrically stimulated left atria isolated from adult rats. The effect of EOAs on the isometric contractions and cardiac frequency in vitro was examined. EOAs decreased rat left atrial force of contraction with an EC₅₀ of 292.2±75.7 μg/ml. Nifedipine, a well known L-type Ca²+ blocker, inhibited in a concentration-dependent manner left atrial force of contraction with an EC₅₀ of 12.1±3.5 μg/ml. Sinus rhythm was diminished by EOAs with an EC₅₀ of 595.4±56.2 μg/ml. Whole-cell L-type Ca²+ currents were recorded by using the patch-clamp technique. EOAs at 25 μg/ml decreased I(Ca,L) by 32.6±9.2% and at 250 μg/ml it decreased by 89.3±7.4%. Thus, inhibition of L-type Ca²+ channels is involved in the cardiodepressive effect elicited by the essential oil of Alpinia speciosa in rat heart.

Exercise training and detraining modify the morphological and mechanical properties of single cardiac myocytes obtained from spontaneously hypertensive rats

We determined the effects of exercise training and detraining on the morphological and mechanical properties of left ventricular myocytes in 4-month-old spontaneously hypertensive rats (SHR) randomly divided into the following groups: sedentary for 8 weeks (SED-8), sedentary for 12 weeks (SED-12), treadmill-running trained for 8 weeks (TRA, 16 m/min, 60 min/day, 5 days/week), and treadmill-running trained for 8 weeks followed by 4 weeks of detraining (DET). At sacrifice, left ventricular myocytes were isolated enzymatically, and resting cell length, width, and cell shortening after stimulation at a frequency of 1 Hz (~25°C) were measured. Cell length was greater in TRA than in SED-8 (161.30 ± 1.01 vs 156.10 ± 1.02 μm, P < 0.05, 667 vs 618 cells, respectively) and remained larger after detraining. Cell width and volume were unaffected by either exercise training or detraining. Cell length to width ratio was higher in TRA than in SED-8 (8.50 ± 0.08 vs 8.22 ± 0.10, P < 0.05) and was maintained after detraining. Exercise training did not affect cell shortening, which was unchanged with detraining. TRA cells exhibited higher maximum velocity of shortening than SED-8 (102.01 ± 4.50 vs 82.01 ± 5.30 μm/s, P < 0.05, 70 cells per group), with almost complete regression after detraining. The maximum velocity of relengthening was higher in TRA cells than in SED-8 (88.20 ± 4.01 vs70.01 ± 4.80 μm/s, P < 0.05), returning to sedentary values with detraining. Therefore, exercise training affected left ventricle remodeling in SHR towards eccentric hypertrophy, which remained after detraining. It also improved single left ventricular myocyte contractile function, which was reversed by detraining.