Rare Presentation of Wide QRS Tachycardia in a Patient in Their 40s.

This article describes the case of a 40-year-old individual who presented with fulminant myocarditis. Initial ECG displayed sinus tachycardia with a heart rate of 117 bpm, QS complexes in leads V1-V3, ST-segment depression in leads II, III, aVF, V5-V6, and ST-segment elevation >0.2 mV in leads V1 through V3. The initial clinical assessment suggested an acute anteroseptal myocardial infarction. However, subsequent diagnostic evaluation through coronary angiography disclosed that the coronary arteries were normal. Therefore, clinicians should carefully consider the differential diagnosis between these conditions, as their management strategies differ markedly. Two hours after admission, the patient unexpectedly developed syncope. The ECG findings were consistent with the typical characteristics of bidirectional ventricular tachycardia. Our report described the appearance and morphology as well as mechanism of bidirectional ventricular tachycardia in detail. Additionally, we delineate differential diagnoses for disease that can cause bidirectional ventricular tachycardia, such as aconite poisoning, digoxin overdose, immune checkpoint inhibitor (ICI), myocardial ischemia, and hereditary channelopathies, such as catecholaminergic polymorphic ventricular tachycardia (CPVT) and Andersen-Tawil syndrome. Therefore, clinicians should recognize this ECG finding immediately and initiate appropriate treatment promptly as these measures may be vital in saving the patient's life.

Empagliflozin treatment rescues abnormally reduced Na+ currents in ventricular cardiomyocytes from dystrophin-deficient mdx mice.

Cardiac arrhythmias significantly contribute to mortality in Duchenne muscular dystrophy (DMD), a severe muscle illness caused by mutations in the gene encoding for the intracellular protein dystrophin. A major source for arrhythmia vulnerability in patients with DMD is impaired ventricular impulse conduction, which predisposes for ventricular asynchrony, decreased cardiac output, and the development of reentrant circuits. Using the dystrophin-deficient mdx mouse model for human DMD, we previously reported that the lack of dystrophin causes a significant loss of peak Na+ current (INa) in ventricular cardiomyocytes. This finding provided a mechanistic explanation for ventricular conduction defects and concomitant arrhythmias in the dystrophic heart. In the present study, we explored the hypothesis that empagliflozin (EMPA), an inhibitor of sodium/glucose cotransporter 2 in clinical use to treat type II diabetes and nondiabetic heart failure, rescues peak INa loss in dystrophin-deficient ventricular cardiomyocytes. We found that INa of cardiomyocytes derived from mdx mice, which had received clinically relevant doses of EMPA for 4 wk, was restored to wild-type level. Moreover, incubation of isolated mdx ventricular cardiomyocytes with 1 µM EMPA for 24 h significantly increased their peak INa. This effect was independent of Na+-H+ exchanger 1 inhibition by the drug. Our findings imply that EMPA treatment can rescue abnormally reduced peak INa of dystrophin-deficient ventricular cardiomyocytes. Long-term EMPA administration may diminish arrhythmia vulnerability in patients with DMD.NEW & NOTEWORTHY Dystrophin deficiency in cardiomyocytes leads to abnormally reduced Na+ currents. These can be rescued by long-term empagliflozin treatment.

New Adamantane-Containing Edaravone Conjugates as Potential Neuroprotective Agents for ALS Treatments.

Currently, there are no effective drugs for the treatment of amyotrophic lateral sclerosis (ALS). Only two drugs-edaravone and riluzole-have been approved, but they have very limited efficacy. The aim of this work was to modify the structural core of the Edaravone-phenylpyrazolone moiety and combine it with aminoadamantane pharmacophore in order to expand the spectrum of its action to a number of processes involved in the pathogenesis of ALS. New conjugates of edaravone derivatives with 1-aminoadamantanes combined with alkylene or hydroxypropylene spacers were synthesized, and their biological activity was investigated. Compounds were found that could inhibit lipid peroxidation and calcium-related mitochondrial permeability, block fast sodium currents of CNS neurons, and reduce aggregation of the mutated form of the FUS-protein typical to ALS. So, the proposed modification of the edaravone molecule has allowed the obtaining of new original structures that combine some prospective therapeutic mechanisms against key chains of the pathogenesis of ALS. The identified lead compounds can be used for further optimization and development of new promising drugs on this basis for the treatment of ALS.

Afferent neurons of the kidney with impaired firing pattern in inflammation - role of sodium currents?

Peripheral neurons with renal afferents exhibit a predominantly tonic firing pattern of higher frequency that is reduced to low frequencies (phasic firing pattern) in renal inflammation. We wanted to test the hypothesis that the reduction in firing activity during inflammation is due to high-activity tonic neurons switching from higher to low frequencies depending on altered sodium currents. We identified and cultivated afferent sensory neurons with renal projections from the dorsal root ganglia (Th11-L2). Cultivated neurons were incubated with the chemokine CXCL1 (1,5 nmol/ml) for 12 h. We characterized neurons as "tonic," i.e., sustained action potential (AP) firing, or "phasic," i.e., < 5 APs upon stimulation in the current clamp. Their membrane currents were investigated in a voltage clamp. Data analyzed: renal vs. non-renal and tonic vs. phasic neurons. Renal afferent neurons exposed to CXCL1 showed a decrease in tonic firing pattern (CXCL1: 35,6% vs. control: 57%, P < 0.05). Na+ and K+ currents were not different between control renal and non-renal DRG neurons. Phasic neurons exhibited higher Na+ and K+ currents than tonic resulting in shorter APs (3.7 ± 0.3 vs. 6.1 ± 0.6 ms, P < 0.01). In neurons incubated with CXCL1, Na+ and K+ peak current density increased in phasic (Na+: - 969 ± 47 vs. - 758 ± 47 nA/pF, P < 0.01; K+: 707 ± 22 vs. 558 ± 31 nA/pF, P < 0.01), but were unchanged in tonic neurons. Phasic neurons exposed to CXCL1 showed a broader range of Na+ currents ([- 365- - 1429 nA] vs. [- 412- - 4273 nA]; P < 0.05) similar to tonic neurons. After CXCL1 exposure, significant changes in phasic neurons were observed in sodium activation/inactivation as well as a wider distribution of Na+ currents characteristic of tonic neurons. These findings indicate a subgroup of tonic neurons besides mere tonic or phasic neurons exists able to exhibit a phasic activity pattern under pathological conditions.

Aluminum alters excitability by inhibiting calcium, sodium, and potassium currents in bovine chromaffin cells.

Aluminum (Al3+ ) has long been related to neurotoxicity and neurological diseases. This study aims to describe the specific actions of this metal on cellular excitability and neurotransmitter release in primary culture of bovine chromaffin cells. Using voltage-clamp and current-clamp recordings with the whole-cell configuration of the patch clamp technique, online measurement of catecholamine release, and measurements of [Ca2+ ]c with Fluo-4-AM, we have observed that Al3+ reduced intracellular calcium concentrations around 25% and decreased catecholamine secretion in a dose-dependent manner, with an IC50 of 89.1 µM. Al3+ blocked calcium currents in a time- and concentration-dependent manner with an IC50 of 560 µM. This blockade was irreversible since it did not recover after washout. Moreover, Al3+ produced a bigger blockade on N-, P-, and Q-type calcium channels subtypes (69.5%) than on L-type channels subtypes (50.5%). Sodium currents were also inhibited by Al3+ in a time- and concentration-dependent manner, 24.3% blockade at the closest concentration to the IC50 (399 µM). This inhibition was reversible. Voltage-dependent potassium currents were low affected by Al3+ . Nonetheless, calcium/voltage-dependent potassium currents were inhibited in a concentration-dependent manner, with an IC50 of 447 µM. This inhibition was related to the depression of calcium influx through voltage-dependent calcium channels subtypes coupled to BK channels. In summary, the blockade of these ionic conductance altered cellular excitability that reduced the action potentials firing and so, the neurotransmitter release and the synaptic transmission. These findings prove that aluminum has neurotoxic properties because it alters neuronal excitability by inhibiting the sodium currents responsible for the generation and propagation of impulse nerve, the potassium current responsible for the termination of action potentials, and the calcium current responsible for the neurotransmitters release.

Diabetes mellitus differently affects electrical membrane properties of vagal afferent neurons of rats.

To study whether diabetes mellitus (DM) would cause electrophysiological alterations in nodose ganglion (NG) neurons, we used patch clamp and intracellular recording for voltage and current clamp configuration, respectively, on cell bodies of NG from rats with DM. Intracellular microelectrodes recording, according to the waveform of the first derivative of the action potential, revealed three neuronal groups (A0 , Ainf , and Cinf ), which were differently affected. Diabetes only depolarized the resting potential of A0 (from -55 to -44 mV) and Cinf (from -49 to -45 mV) somas. In Ainf neurons, diabetes increased action potential and the after-hyperpolarization durations (from 1.9 and 18 to 2.3 and 32 ms, respectively) and reduced dV/dtdesc (from -63 to -52 V s-1 ). Diabetes reduced the action potential amplitude while increasing the after-hyperpolarization amplitude of Cinf neurons (from 83 and -14 mV to 75 and -16 mV, respectively). Using whole cell patch clamp recording, we observed that diabetes produced an increase in peak amplitude of sodium current density (from -68 to -176 pA pF-1 ) and displacement of steady-state inactivation to more negative values of transmembrane potential only in a group of neurons from diabetic animals (DB2). In the other group (DB1), diabetes did not change this parameter (-58 pA pF-1 ). This change in sodium current did not cause an increase in membrane excitability, probably explainable by the alterations in sodium current kinetics, which are also induced by diabetes. Our data demonstrate that diabetes differently affects membrane properties of different nodose neuron subpopulations, which likely have pathophysiological implications for diabetes mellitus.

Synthesis and evaluation of a novel analgesic conotoxin Lt7b that inhibits calcium currents and increases sodium currents.

Conotoxins are promising neuropharmacological tools and drug candidates due to their high efficiency and specificity in targeting ion channels or neurotransmitter receptors. In this study, a novel O2 -superfamily conotoxin, Lt7b, was synthesized and its pharmacological functions were evaluated. Lt7b with three modified amino acids and three disulfide bonds was successfully synthesized. CD spectra showed that Lt7b had a typical α-helix in the secondary structure. Patch clamp experiments on rat DRG neurons showed that Lt7b could significantly inhibit calcium currents with an IC50 value of 856 ± 95 nM. Meanwhile, 10 µM Lt7b could significantly increase the sodium currents by 77 ± 8%, but it had no obvious effects on the potassium currents in DRG neurons. In addition, patch clamp experiments on ion channel subtypes showed that 10 µM Lt7b could inhibit 7.0 ± 1.2%, 8.0 ± 1.5%, 4.6 ± 3.4%, and 9.5 ± 0.1% of the hCav 1.2, hCav 2.1, hCav 2.2, and hCav 3.2 currents, respectively, while it did not increase the rNav 1.7, rNav 1.8, hNav 1.5, hNav 1.7, and hNav 1.8 currents. Lt7b had no obvious toxicity to HaCaT and ND7/23 cells up to 1 mM and significantly increased the pain threshold at the testing time of 0.5-4 h in a dose-dependent manner in the mouse hotplate assay. This novel conotoxin Lt7b may be a useful tool for ion channel studies and analgesic drug development.

Identification of Sodium Transients Through NaV1.5 Channels as Regulators of Differentiation in Immortalized Dorsal Root Ganglia Neurons.

Neuronal differentiation is a complex process through which newborn neurons acquire the morphology of mature neurons and become excitable. We employed a combination of functional and transcriptomic approaches to deconvolute and identify key regulators of the differentiation process of a DRG neuron-derived cell line, and we focused our study on the Na V 1.5 ion channel (encoded by Scn5a) as a channel involved in the acquisition of DRG neuronal features. Overexpression of Scn5a enhances the acquisition of neuronal phenotypic features and increases the KCl-elicited hyperexcitability response in a DRG-derived cell line. Moreover, pharmacologic inhibition of the Na V 1.5 channel during differentiation hinders the acquisition of phenotypic features of neuronal cells and the hyperexcitability increase in response to changes in the extracellular medium ionic composition. Taken together, these data highlight the relevance of sodium transients in regulating the neuronal differentiation process in a DRG neuron-derived cell line.

Prefrontal cortex pyramidal neurons express functional Nav1.8 tetrodotoxin-resistant sodium currents.

It has been repeatedly proved that Nav1.8 tetrodotoxin (TTX)-resistant sodium currents are expressed in peripheral sensory neurons where they play important role in nociception. There are very few publications that show the presence of TTX-resistant sodium currents in central neurons. The aim of this study was to assess if functional Nav1.8 TTX-resistant sodium currents are expressed in prefrontal cortex pyramidal neurons. All recordings were performed in the presence of TTX in the extracellular solution to block TTX-sensitive sodium currents. The TTX-resistant sodium current recorded in this study was mainly carried by the Nav1.8 sodium channel isoform because the Nav1.9 current was inhibited by the -65 mV holding potential that we used throughout the study. Moreover, the sodium current that we recorded was inhibited by treatment with the selective Nav1.8 inhibitor A-803467. Confocal microscopy experiments confirmed the presence of the Nav1.8 α subunit in prefrontal cortex pyramidal neurons. Activation and steady state inactivation properties of TTX-resistant sodium currents were also assessed in this study and they were similar to activation and inactivation properties of TTX-resistant sodium currents expressed in dorsal root ganglia (DRG) neurons. Moreover, this study showed that carbamazepine (60 µM) inhibited the maximal amplitude of the TTX-resistant sodium current. Furthermore, we found that carbamazepine shifts steady state inactivation curve of TTX-resistant sodium currents toward hyperpolarization. This study suggests that the Nav1.8 TTX-resistant sodium channel is expressed not only in DRG neurons, but also in cortical neurons and may be molecular target for antiepileptic drugs such as carbamazepine.

Distinctive Properties and Powerful Neuromodulation of Nav1.6 Sodium Channels Regulates Neuronal Excitability.

Voltage-gated sodium channels (Navs) are critical determinants of cellular excitability. These ion channels exist as large heteromultimeric structures and their activity is tightly controlled. In neurons, the isoform Nav1.6 is highly enriched at the axon initial segment and nodes, making it critical for the initiation and propagation of neuronal impulses. Changes in Nav1.6 expression and function profoundly impact the input-output properties of neurons in normal and pathological conditions. While mutations in Nav1.6 may cause channel dysfunction, aberrant changes may also be the result of complex modes of regulation, including various protein-protein interactions and post-translational modifications, which can alter membrane excitability and neuronal firing properties. Despite decades of research, the complexities of Nav1.6 modulation in health and disease are still being determined. While some modulatory mechanisms have similar effects on other Nav isoforms, others are isoform-specific. Additionally, considerable progress has been made toward understanding how individual protein interactions and/or modifications affect Nav1.6 function. However, there is still more to be learned about how these different modes of modulation interact. Here, we examine the role of Nav1.6 in neuronal function and provide a thorough review of this channel's complex regulatory mechanisms and how they may contribute to neuromodulation.

A novel proline-rich M-superfamily conotoxin that can simultaneously affect sodium, potassium and calcium currents.

BACKGROUND: Conotoxins have become a research hotspot in the neuropharmacology field for their high activity and specificity in targeting ion channels and neurotransmitter receptors. There have been reports of a conotoxin acting on two ion channels, but rare reports of a conotoxin acting on three ion channels. METHODS: Vr3a, a proline-rich M-superfamily conotoxin from a worm-hunting Conus varius, was obtained by solid-phase synthesis and identified by mass spectrometry. The effects of synthesized Vr3a on sodium, potassium and calcium currents were tested on rat DRG cells by patch clamp experiments. The further effects of Vr3a on human Cav1.2 and Cav2.2 currents were tested on HEK293 cells. RESULTS: About 10 µM Vr3a has no effects on the peak sodium currents, but can induce a ~10 mV shift in a polarizing direction in the current-voltage relationship. In addition, 10 µM Vr3a can increase 19.61 ± 5.12% of the peak potassium currents and do not induce a shift in the current-voltage relationship. An amount of 10 µM Vr3a can inhibit 31.26% ± 4.53% of the peak calcium currents and do not induce a shift in the current-voltage relationship. The IC50 value of Vr3a on calcium channel currents in rat DRG neurons is 19.28 ± 4.32 µM. Moreover, 10 µM Vr3a can inhibit 15.32% ± 5.41% of the human Cav1.2 currents and 12.86% ± 4.93% of the human Cav2.2 currents. CONCLUSIONS: Vr3a can simultaneously affect sodium, potassium and calcium currents. This novel triple-target conotoxin Vr3a expands understanding of conotoxin functions.

Slow recovery from the inactivation of voltage-gated sodium channel Nav1.3 in mouse taste receptor cells.

Action potentials play an important role in neurotransmitter release in response to taste. Here, I have investigated voltage-gated Na+ channels, a primary component of action potentials, in respective cell types of mouse fungiform taste bud cells (TBCs) with in situ whole-cell clamping and single-cell RT-PCR techniques. The cell types of TBCs electrophysiologically examined were determined immunohistochemically using the type III inositol 1,4,5-triphoshate receptor as a type II cell marker and synaptosomal-associated protein 25 as a type III cell marker. I show that type II cells, type III cells, and TBCs not immunoreactive to these markers (likely type I cells) generate voltage-gated Na+ currents. The recovery following inactivation of these currents was well fitted with double exponential curves. The time constants in type III cells (~20 ms and ~ 1 s) were significantly slower than respective time constants in other cell types. RT-PCR analysis indicated the expression of Nav1.3, Nav1.5, Nav1.6, and ß1 subunit mRNAs in TBCs. Pharmacological inhibition and single-cell RT-PCR studies demonstrated that type II and type III cells principally express tetrodotoxin (TTX)-sensitive Nav1.3 channels and that ~ 30% of type I cells express TTX-resistant Nav1.5 channels. The auxiliary ß1 subunit that modulates gating kinetics was rarely detected in TBCs. As the ß1 subunit co-expressed with an α subunit is known to accelerate the recovery from inactivation, it is likely that voltage-gated Na+ channels in TBCs may function without ß subunits. Slow recovery from inactivation, especially in type III cells, may limit high-frequency firing in response to taste substances.

Multiple arrhythmic and cardiomyopathic phenotypes associated with an SCN5A A735E mutation.

BACKGROUND: SCN5A mutations are associated with multiple arrhythmic and cardiomyopathic phenotypes including Brugada syndrome (BrS), sinus node dysfunction (SND), atrioventricular block, supraventricular tachyarrhythmias (SVTs), long QT syndrome (LQTS), dilated cardiomyopathy and left ventricular noncompaction. Several single SCN5A mutations have been associated with overlap of some of these phenotypes, but never with overlap of all the phenotypes. OBJECTIVE: We encountered two pedigrees with multiple arrhythmic phenotypes with or without cardiomyopathic phenotypes, and sought to identify a responsible mutation and reveal its functional abnormalities. METHODS: Target panel sequencing of 72 genes, including inherited arrhythmia syndromes- and cardiomyopathies-related genes, was employed in two probands. Cascade screening was performed by Saner sequencing. Wild-type or identified mutant SCN5A were expressed in tsA201 cells, and whole-cell sodium currents (INa) were recorded using patch-clamp techniques. RESULTS: We identified an SCN5A A735E mutation in these probands, but did not identify any other mutations. All eight mutation carriers exhibited at least one of the arrhythmic phenotypes. Two patients exhibited multiple arrhythmic phenotypes: one (15-year-old girl) exhibited BrS, SND, and exercise and epinephrine-induced QT prolongation, the other (4-year-old boy) exhibited BrS, SND, and SVTs. Another one (30-year-old male) exhibited all arrhythmic and cardiomyopathic phenotypes, except for LQTS. One male suddenly died at age 22. Functional analysis revealed that the mutant did not produce functional INa. CONCLUSIONS: A non-functional SCN5A A735E mutation could be associated with multiple arrhythmic and cardiomyopathic phenotypes, although there remains a possibility that other unidentified factors may be involved in the phenotypic variability of the mutation carriers.

Effects of modulation on sodium and potassium channel currents by extremely low frequency electromagnetic fields stimulation on hippocampal CA1 pyramidal cells.

To investigate the effects of extremely low-frequency electromagnetic fields (ELF-EMFs) stimulation on sodium channel currents (INa), transient outward potassium channel currents (IA) and delayed rectifier potassium channel currents (IK) on hippocampal CA1 pyramidal neurons of young Sprague-Dawley rats. CA1 pyramidal neurons of rat hippocampal slices were subjected to ELF-EMFs stimulation with different frequencies (15 and 50 Hz), intensities (0.5, 1 and 2 mT) and durations (10, 20 and 30 min). The INa, IA and IK of neurons were recorded by a whole-cell patch-clamp method. ELF-EMFs stimulation enhanced INa densities, and depressed IA and IK densities. In detail, INa was more sensitive to the variation of intensities and frequencies of ELF-EMFs, whereas IA and IK were mainly affected by the variation of the duration of ELF-EMFs. ELF-EMFs stimulation altered activation and deactivation properties of INa, IA and IK. ELF-EMFs stimulation plays a role as a regulator rather than an inducer for ion channels. It might change the transition probability of ion channel opening or closing, and might also change the structure and function of the ion channel which need to be proved by the further technical method.

Sex-specific IKAS activation in rabbit ventricles with drug-induced QT prolongation.

BACKGROUND: Female sex is a known risk factor for drug-induced long QT syndrome (diLQTS). We recently demonstrated a sex difference in apamin-sensitive small-conductance Ca2+-activated K+ current (IKAS) activation during ß-adrenergic stimulation. OBJECTIVE: The purpose of this study was to test the hypothesis that there is a sex difference in IKAS in the rabbit models of diLQTS. METHODS: We evaluated the sex difference in ventricular repolarization in 15 male and 22 female Langendorff-perfused rabbit hearts with optical mapping techniques during atrial pacing. HMR1556 (slowly activating delayed rectifier K+ current [IKs] blocker), E4031 (rapidly activating delayed rectifier K+ current [IKr] blocker) and sea anemone toxin (ATX-II, late Na+ current [INaL] activator) were used to simulate types 1-3 long QT syndrome, respectively. Apamin, an IKAS blocker, was then added to determine the magnitude of further QT prolongation. RESULTS: HMR1556, E4031, and ATX-II led to the prolongation of action potential duration at 80% repolarization (APD80) in both male and female ventricles at pacing cycle lengths of 300-400 ms. Apamin further prolonged APD80 (pacing cycle length 350 ms) from 187.8±4.3 to 206.9±7.1 (P=.014) in HMR1556-treated, from 209.9±7.8 to 224.9±7.8 (P=.003) in E4031-treated, and from 174.3±3.3 to 188.1±3.0 (P=.0002) in ATX-II-treated female hearts. Apamin did not further prolong the APD80 in male hearts. The Cai transient duration (CaiTD) was significantly longer in diLQTS than baseline but without sex differences. Apamin did not change CaiTD. CONCLUSION: We conclude that IKAS is abundantly increased in female but not in male ventricles with diLQTS. Increased IKAS helps preserve the repolarization reserve in female ventricles treated with IKs and IKr blockers or INaL activators.

A novel proline-rich M-superfamily conotoxin that can simultaneously affect sodium, potassium and calcium currents

Background Conotoxins have become a research hotspot in the neuropharmacology field for their high activity and specificity in targeting ion channels and neurotransmitter receptors. There have been reports of a conotoxin acting on two ion channels, but rare reports of a conotoxin acting on three ion channels. Methods Vr3a, a proline-rich M-superfamily conotoxin from a worm-hunting Conus varius, was obtained by solid-phase synthesis and identified by mass spectrometry. The effects of synthesized Vr3a on sodium, potassium and calcium currents were tested on rat DRG cells by patch clamp experiments. The further effects of Vr3a on human Cav1.2 and Cav2.2 currents were tested on HEK293 cells. Results About 10 μM Vr3a has no effects on the peak sodium currents, but can induce a ~10 mV shift in a polarizing direction in the current-voltage relationship. In addition, 10 μM Vr3a can increase 19.61 ± 5.12% of the peak potassium currents and do not induce a shift in the current-voltage relationship. An amount of 10 μM Vr3a can inhibit 31.26% ± 4.53% of the peak calcium currents and do not induce a shift in the current-voltage relationship. The IC50 value of Vr3a on calcium channel currents in rat DRG neurons is 19.28 ± 4.32 μM. Moreover, 10 μM Vr3a can inhibit 15.32% ± 5.41% of the human Cav1.2 currents and 12.86% ± 4.93% of the human Cav2.2 currents. Conclusions Vr3a can simultaneously affect sodium, potassium and calcium currents. This novel triple-target conotoxin Vr3a expands understanding of conotoxin functions.(AU)

Biophysical defects of an SCN5A V1667I mutation associated with epinephrine-induced marked QT prolongation.

BACKGROUND: The epinephrine infusion test (EIT) typically induces marked QT prolongation in LQT1, but not LQT3, while the efficacy of ß-blocker therapy is established in LQT1, but not LQT3. We encountered an LQT3 family, with an SCN5A V1667I mutation, that exhibited epinephrine-induced marked QT prolongation. METHODS: Wild-type (WT) or V1667I-SCN5A was transiently expressed into tsA-201 cells, and whole-cell sodium currents (INa ) were recorded using patch-clamp techniques. To mimic the effects of epinephrine, INa was recorded after the application of protein kinase A (PKA) activator, 8-CPT-cAMP (200 µM), for 10 minutes. RESULTS: The peak density of V1667I-INa was significantly larger than WT-INa (WT: 469 ± 48 pA/pF, n = 20; V1667I: 690 ± 62 pA/pF, n = 19, P < .01). The steady-state activation (SSA) and fast inactivation rate of V1667I-INa were comparable to WT-INa . V1667I-INa displayed a significant depolarizing shift in steady-state inactivation (SSI) in comparison to WT-INa (V1/2 -WT: -88.1 ± 0.8 mV, n = 17; V1667I: -82.5 ± 1.1 mV, n = 17, P < .01), which increases window currents. Tetrodotoxin (30 µM)-sensitive persistent V1667I-INa was comparable to WT-INa . However, the ramp pulse protocol (RPP) displayed an increased hump in V1667I-INa in comparison to WT-INa . Although 8-CPT-cAMP shifted SSA to hyperpolarizing potentials in WT-INa and V1667I-INa to the same extent, it shifted SSI to hyperpolarizing potentials much less in V1667I-INa than in WT-INa (V1/2 -WT: -92.7 ± 1.3 mV, n = 6; V1667I: -85.3 ± 1.6 mV, n = 6, P < .01). Concordantly, the RPP displayed an increased hump in V1667I-INa , but not in WT-INa . CONCLUSIONS: We demonstrated an increase of V1667I-INa by PKA activation, which may provide a rationale for the efficacy of ß-blocker therapy in some cases of LQT3.

Effect of carvedilol on atrial excitation-contraction coupling, Ca2+ release, and arrhythmogenicity.

Carvedilol is an FDA-approved ß-blocker commonly used for treatment of high blood pressure, congestive heart failure, and cardiac tachyarrhythmias, including atrial fibrillation. We investigated at the cellular level the mechanisms through which carvedilol interferes with sarcoplasmic reticulum (SR) Ca2+ release during excitation-contraction coupling (ECC) in single rabbit atrial myocytes. Carvedilol caused concentration-dependent (1-10 µM) failure of SR Ca2+ release. Failure of ECC and Ca2+ release was the result of dose-dependent inhibition of voltage-gated Na+ (INa) and L-type Ca2+ (ICa) currents that are responsible for the rapid depolarization phase of the cardiac action potential (AP) and the initiation of Ca2+-induced Ca2+ release from the SR, respectively. Carvedilol (1 µM) led to AP duration shortening, AP failures, and peak INa inhibition by ~80%, whereas ICa was not markedly affected. Carvedilol (10 µM) blocked INa almost completely and reduced ICa by ~40%. No effect on Ca2+-transient amplitude, ICa, and INa was observed in control experiments with the ß-blocker metoprolol, suggesting that the carvedilol effect on ECC is unlikely the result of its ß-blocking property. The effects of carvedilol (1 µM) on subcellular SR Ca2+ release was spatially inhomogeneous, where a selective inhibition of peripheral subsarcolemmal Ca2+ release from the junctional SR accounted for the cell-averaged reduction in Ca2+-transient amplitude. Furthermore, carvedilol significantly reduced the probability of spontaneous arrhythmogenic Ca2+ waves without changes of SR Ca2+ load. The data suggest a profound antiarrhythmic action of carvedilol in atrial myocytes resulting from an inhibitory effect on the SR Ca2+ release channel.NEW & NOTEWORTHY Here we show that the clinically widely used ß-blocker carvedilol has profound effects on Ca2+ signaling and ion currents, but also antiarrhythmic effects in adult atrial myocytes. Carvedilol inhibits sodium and calcium currents and leads to failure of ECC but also prevents spontaneous Ca2+ release from cellular sarcoplasmic reticulum (SR) Ca2+ stores in form of arrhythmogenic Ca2+ waves. The antiarrhythmic effect occurs by carvedilol acting directly on the SR ryanodine receptor Ca2+ release channel.

Enhanced closed-state inactivation of mutant cardiac sodium channels (SCN5A N1541D and R1632C) through different mechanisms.

BACKGROUND: SCN5A variants can be associated with overlapping phenotypes such as Brugada syndrome (BrS), sinus node dysfunction and supraventricular tachyarrhythmias. Our genetic screening of SCN5A in 65 consecutive BrS probands revealed two patients with overlapping phenotypes: one carried an SCN5A R1632C (in domain IV-segment 4), which we have previously reported, the other carried a novel SCN5A N1541D (in domain IV-segment 1). OBJECTIVE: We sought to reveal whether or not these variants are associated with the same biophysical defects. METHODS: Wild-type (WT) or mutant SCN5A was expressed in tsA201-cells, and whole-cell sodium currents (hNav1.5/INa) were recorded using patch-clamp techniques. RESULTS: The N1541D-INa density, when assessed from a holding potential of -150 mV, was not different from WT-INa as with R1632C-INa, indicating that SCN5A N1541D did not cause trafficking defects. The steady-state inactivation curve of N1541D-INa was markedly shifted to hyperpolarizing potentials in comparison to WT-INa (V1/2-WT: -82.3 ±â€¯0.9 mV, n = 15; N1541D: -108.8 ±â€¯1.6 mV, n = 26, P < .01) as with R1632C-INa. Closed-state inactivation (CSI) was evaluated using prepulses of -90 mV for 1460 ms. Residual N1541D-INa and R1632C-INa were markedly reduced in comparison to WT-INa (WT: 63.8 ±â€¯4.6%, n = 18; N1541D: 15.1 ±â€¯2.3%, n = 19, P < .01 vs WT; R1632C: 5.3 ±â€¯0.5%, n = 15, P < .01 vs WT). Entry into CSI of N1541D-INa was markedly accelerated, and that of R1632C-INa was weakly accelerated in comparison to WT-INa (tau-WT: 65.8 ±â€¯7.4 ms, n = 18; N1541D: 13.7 ±â€¯1.1 ms, n = 19, P < .01 vs WT; R1632C: 39.5 ±â€¯2.9 ms, n = 15, P < .01 vs WT and N1541D). Although N1541D-INa recovered from closed-state fast inactivation at the same rate as WT-INa, R1632C-INa recovered very slowly (tau-WT: 1.90 ±â€¯0.16 ms, n = 10; N1541D: 1.72 ±â€¯0.12 ms, n = 10, P = .41 vs WT; R1632C: 53.0 ±â€¯2.5 ms, n = 14, P < .01 vs WT and N1541D). CONCLUSIONS: Both N1541D-INa and R1632C-INa exhibited marked enhancement of CSI, but through different mechanisms. The data provided a novel understanding of the mechanisms of CSI of INa. Clinically, the enhanced CSI of N1541D-INa leads to a severe loss-of-function of INa at voltages near the physiological resting membrane potential (~-90 mV) of cardiac myocytes; this can be attributable to the patient's phenotypic manifestations.

Feeding cycle alters the biophysics and molecular expression of voltage-gated Na+ currents in rat hippocampal CA1 neurones.

The function of hippocampus as a hub for energy balance is a subject of broad and current interest. This study aims at providing more evidence on this regard by addressing the effects of feeding cycle on the voltage-gated sodium (Na+ ) currents of acutely isolated Wistar rat hippocampal CA1 neurones. Specifically, by applying patch clamp techniques (whole cell voltage clamp and single channel in inside-out patches) we assessed the influence of feeding and fasting conditions on the intrinsic biophysical properties of Na+ currents. Additionally, mass spectrometry and western blotting experiments were used to address the effect of feeding cycle over the Na+ channel population of the rat hippocampus. Na+ currents were recorded in neurones obtained from fed and fasted animals (here termed "fed neurones" and "fasted neurones", respectively). Whole cell Na+ currents of fed neurones, as compared to fasted neurones, showed increased mean maximum current density and a higher "window current" amplitude. We demonstrate that these results are supported by an increased single channel Na+ conductance in fed neurones and, also, by a greater Nav1.2 channel density in plasma membrane-enriched fractions of fed samples (but not in whole hippocampus preparations). These results imply fast variations on the biophysics and molecular expression of Na+ currents of rat hippocampal CA1 neurones, throughout the feeding cycle. Thus, one may expect a differentiated regulation of the intrinsic neuronal excitability, which may account for the role of the hippocampus as a processor of satiety information.