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.

The insecticide ß-Cyfluthrin induces acute arrhythmic cardiotoxicity through interaction with NaV1.5 and ranolazine reverses the phenotype.

ß-Cyfluthrin, a class II Pyrethroid, is an insecticide used worldwide in agriculture, horticulture (field and protected crops), viticulture, and domestic applications. ß-Cyfluthrin may impair the function of biological systems; however, little information is available about its potential cardiotoxic effect. Here, we explored the acute toxicity of ß-Cyfluthrin in isolated heart preparations and its cellular basis, using isolated cardiomyocytes. Moreover, ß-Cyfluthrin effects on the sodium current, especially late sodium current (INa-L), were investigated using human embryonic kidney cells (HEK-293) cells transiently expressing human NaV1.5 channels. We report that ß-Cyfluthrin raised INa-L in a dose-dependent manner. ß-Cyfluthrin prolonged the repolarization of the action potential (AP) and triggered oscillations on its duration. Cardiomyocytes contraction and calcium dynamics were disrupted by the pesticide with a marked incidence of non-electronic-stimulated contractions. The antiarrhythmic drug Ranolazine was able to reverse most of the phenotypes observed in isolated cells. Lastly, ventricular premature beats (VPBs) and long QT intervals were found during ß-Cyfluthrin exposure, and Ranolazine was able to attenuate them. Overall, we demonstrated that ß-Cyfluthrin can cause significant cardiac alterations and Ranolazine ameliorated the phenotype. Understanding the insecticides' impacts upon electromechanical properties of the heart is important for the development of therapeutic approaches to treat cases of pesticides intoxication.

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.

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.