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The voltage-gated sodium NaV1.7 channel plays a key role as a mediator of action potential propagation in C-fiber nociceptors and is an established molecular target for pain therapy. ProTx-II is a potent and moderately selective peptide toxin from tarantula venom that inhibits human NaV1.7 activation. Here we used available structural and experimental data to guide Rosetta design of potent and selective ProTx-II-based peptide inhibitors of human NaV1.7 channels. Functional testing of designed peptides using electrophysiology identified the PTx2-3127 and PTx2-3258 peptides with IC50s of 7 nM and 4 nM for hNaV1.7 and more than 1000-fold selectivity over human NaV1.1, NaV1.3, NaV1.4, NaV1.5, NaV1.8, and NaV1.9 channels. PTx2-3127 inhibits NaV1.7 currents in mouse and human sensory neurons and shows efficacy in rat models of chronic and thermal pain when administered intrathecally. Rationally designed peptide inhibitors of human NaV1.7 channels have transformative potential to define a new class of biologics to treat pain.

Men have a higher risk of developing atrial fibrillation (AF) than women, though the reason for this is unknown. Here, we compared atrial electrical and structural properties in male and female mice and explored the contribution of sex hormones. Cellular electrophysiological studies revealed that action potential configuration, Na+ and K+ currents were similar in atrial myocytes from male and female mice (4–5 months). Immunofluorescence showed that male atrial myocytes had more lateralization of connexins 40 (63 ± 4%) and 43 (66 ± 4%) than females (Cx40: 45 ± 4%, p = 0.006; Cx43: 44 ± 4%, p = 0.002), with no difference in mRNA expression. Atrial mass was significantly higher in males. Atrial myocyte dimensions were also larger in males. Atrial fibrosis was low and similar between sexes. Orchiectomy (ORC) abolished sex differences in AF susceptibility (M: 65%; ORC: 38%, p = 0.050) by reducing connexin lateralization and myocyte dimensions. Ovariectomy (OVX) did not influence AF susceptibility (F: 42%; OVX: 33%). This study shows that prior to the development of age-related remodeling, male mice have more connexin lateralization and larger atria and atrial myocyte than females. Orchiectomy reduced AF susceptibility in males by decreasing connexin lateralization and atrial myocyte size, supporting a role for androgens. These sex differences in AF substrates may contribute to male predisposition to AF.

Late sodium current (late INa) inhibition has been proposed to suppress the incidence of arrhythmias generated by pathological states or induced by drugs. However, the role of late INa in the human heart is still poorly understood. We therefore investigated the role of this conductance in arrhythmias using adult primary cardiomyocytes and tissues from donor hearts. Potentiation of late INa with ATX-II (anemonia sulcata toxin II) and E-4031 (selective blocker of the hERG channel) slowed the kinetics of action potential repolarization, impaired Ca2+ homeostasis, increased contractility, and increased the manifestation of arrhythmia markers. These effects could be reversed by late INa inhibitors, ranolazine and GS-967. We also report that atrial tissues from donor hearts affected by atrial fibrillation exhibit arrhythmia markers in the absence of drug treatment and inhibition of late INa with GS-967 leads to a significant reduction in arrhythmic behaviour. These findings reveal a critical role for the late INa in cardiac arrhythmias and suggest that inhibition of this conductance could provide an effective therapeutic strategy. Finally, this study highlights the utility of human ex-vivo heart models for advancing cardiac translational sciences.

Background In utero exposure to tobacco smoke is associated with sudden infant death syndrome (SIDS) and cardiac arrhythmias in newborns. The arrhythmogenic mechanisms seem linked to alterations of the cardiac sodium current (INa). We previously reported that in utero exposure to nicotine delays the postnatal development of the heart sinoatrial node in rabbits and altered expression of the sodium channels NaV1.5 and NaV1.1 in the atrium surrounding it. These channels react differently to sympathetic stimulation. Objective The purpose of this study was to test whether nicotine altered the response of INa to stimulation by the β-adrenoreceptor agonist isoproterenol in atrial myocytes. Our hypothesis is that changes in the sympathetic response of sinoatrial node peripheral cells may create a substrate for arrhythmia. Methods Using the patch-clamp technique we measured the effect of nicotine on the response of INa to adrenergic stimulation in isolated cardiomyocytes. Results Isoproterenol increased INa by 50% in newborn sham rabbits but had no effect in newborn rabbits exposed to nicotine in utero. Our data also show that nicotine increases the late sodium current, an effect that may promote QT prolongation. Conclusion We provide the first evidence linking fetal exposure to nicotine to long-term alterations of INa response to isoproterenol. These changes may impair INa adaptation to sympathetic tone and prevent awakening from sleep apnea, thus leading to arrhythmias that could potentially be involved in SIDS. Our data also raise concerns about the use of nicotine replacement therapies for pregnant women.

Introduction: Infarcts are responsible for cardiac arrhythmias and transient ischemic episodes. It has been demonstrated that the neuronal sodium channels (nNavs) are overexpressed around an ischemic area. Ischemias induce a depolarization of the membrane potential and it's known that nNavs channels activate at more depolarized potentials than the cardiac sodium channels (Nav1.5). We hypothesised that this overexpression of nNavs channels may act as a safety factor for cardiac conduction during ischemia. However, the nNavs have a larger late component than Nav1.5 therefore prolonging the action potential duration (APD) and creating an arrythmogenic substrate (AS). The aim of this study is to estimate the contribution of the nNavs in the late sodium current (INaL) in ischemic condition in order to determine if an overexpression of the nNavs can modify the APD and create an AS.Methods: Freshly isolated cardiomyocytes were placed under ischemic conditions for 45 minutes. INaL currents were recorded with the patch clamp technique in whole cell configuration. Tetrodotoxin (a specific nNavs blocker) and MTSEA (a specific Nav1.5 blocker) were used to differentiate the two sodium channels isoforms.Results: In normal condition, nNavs account for 11% of peak current. INaL represents 0.3% of the peak current at a potential of −10 mV. Contribution of nNavs (TTX sensitive) to INaL was 36% ± 5%. Ischemia decreases the maximal current density from −73.3 nA/pF to −53.4 nA/pF. Surprisingly, nNavs contribution was not modified (10% of the peak current). However, ischemia increases INaL from 0.3% to 1.6% compared to the peak current.Conclusion: Ischemia increases by 5.3 times INaL that can play a critical role in the duration of the action potential and facilitates the outcome of arrhythmias.

More than 50% of newborns death is due to the sudden infant death syndrome (SIDS). Exposure to cigarette smoke represents the highest risk factor for SIDS. Cardiac bradycardias are observed in most cases. The cardiac conduction system is molded by a resorptive degeneration process (apoptosis). Nicotine is known to possess anti-apoptotic effects. Therefore, we hypothesized that nicotine disrupts the maturation of the sinoatrial (SAN) and auriculoventricular (AVN) nodes, which in return can cause arrhythmias leading to SIDS.Osmotic pumps delivering nicotine were implanted in rabbits at their second week of pregnancy. We characterized the level of apoptosis in SAN of newborn rabbits exposed or not to nicotine. Moreover, we did patch clamp techniques to evaluate the effects of nicotine on adrenergic responses. Finally, using quantitative PCR, we quantified the expression of sodium channels in the atria of the rabbits’ hearts at 0, 7, 14 and 30 days postnatal.Nicotine decreased apoptosis at 7 days postnatal, thus preventing the early development of SAN. At 14 and 30 days when serum nicotine levels reached 0 ng/ml, apoptosis reached levels similar to unexposed rabbit at 7 days. Nicotine inverted the expression pattern of SCN1A and SCN5A in the SAN of rabbits at 0 day postnatal and increased the expression of SCN5A by 70 times in the right atrium at 30 days postnatal. Expression of SCN1A and SCN4A increased by 4 fold in the 0 day old treated rabbit in the atria. Finally, nicotine suppresses the effect of isoproterenol on sodium channels.In conclusion, our study demonstrates that nicotine disturbed the resorptive degeneration process, delays the development of the SAN and regionally perturbed the expression of SCN1A, SCN4A and SCN5A. These changes might explain the conduction disturbances observed in SIDS.