scholarly journals The SCN5A point mutation M1875T, associated with familial atrial fibrillation, causes a gain-of-function effect of the cardiac Nav1.5 channel in atrial cardiomyocytes

EP Europace ◽  
2021 ◽  
Vol 23 (Supplement_3) ◽  
Author(s):  
M O"reilly ◽  
L Sommerfeld ◽  
C O"shea ◽  
S Broadway-Stringer ◽  
S Kabir ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Protein Expression ◽  
Point Mutation ◽  
Na Channel ◽  
Na Current ◽  
Α Subunit ◽  
Atrial Cardiomyocytes ◽  
Familial Atrial Fibrillation ◽  
And Function ◽  
Scn5a Gene

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): British Heart Foundation Leducq Foundation Background The point mutation M1875T in the SCN5A gene, which encodes the pore-forming α-subunit of the cardiac voltage-gated Na+ channel Nav1.5, has been associated with familial atrial fibrillation (AF), but its effects on atrial cardiomyocyte electrophysiology is unclear. Aim To investigate the effect of the point mutation M1875T on atrial electrophysiological parameters. Methods In a novel heterozygous knock-in murine model (Scn5a-M1875T+/-), whole-cell patch clamp electrophysiology was used to investigate Na+ currents in left atrial (LA) cardiomyocytes isolated from hearts of young adult mice (10-16 weeks). LA microelectrode and optical mapping recordings were used to study action potential (AP) characteristics. Cardiac size and function were measured by transthoracic echocardiography. Atrial Scn5a gene and Nav1.5 protein expression were assessed by Rt-PCR and Western blot. Results The Na+ current was increased in cardiomyocytes isolated from Scn5a-M1875T+/- LA (wildtype (WT) -22.7 ± 0.9 pA/pF (N = 14, n = 115); Scn5a-M1875T+/- -28.3 ± 1.1 pA/pF (N = 15, n = 117)). Scn5a-M1875T+/- intact isolated superfused LA had an elevated AP amplitude (100 ms pacing cycle length (PCL): WT 86.4 ± 0.9 mV (N = 8, n = 24); Scn5a-M1875T+/- 91.2 ± 0.7 mV (N = 8, n = 25)) and a faster peak upstroke velocity (100 ms PCL: WT 127.98 ± 3.28 mV/ms; Scn5a-M1875T+/- 142.80 ± 3.98 mV/ms). AP duration (APD) was not different apart from a small APD shortening at slow rates. Echocardiography revealed no difference in size and function at the age of investigation. Atrial Scn5a gene and Nav1.5 protein expression were comparable. When challenged with flecainide (1 µM), Scn5a-M1875T+/- LA showed less conduction slowing than WT (100 ms PCL: WT -10.43 ± 1.27 cm/s (N = 12); Scn5a-M1875T+/- -6.10 ± 1.34 cm/s (N = 12)).  5 µM flecainide caused significant increase in WT refractoriness (7/12 atria lost 1:1 capture at PCL ≤ 120 ms) compared to Scn5a-M1875T+/- (1/12). Conclusion(s): SCN5A point mutation M1875T increases the Na+ current in atrial cardiomyocytes and intact atria, leading to a faster AP upstroke and an attenuated response to flecainide. Abstract Figure 1: Current-Voltage relationship

scholarly journals Post-translational modifications of the cardiac Na channel: contribution of CaMKII-dependent phosphorylation to acquired arrhythmias

2013 ◽  
Vol 305 (4) ◽  
pp. H431-H445 ◽  
Author(s):  
Anthony W. Herren ◽  
Donald M. Bers ◽  
Eleonora Grandi
Keyword(s):  
Heart Failure ◽  
Na Channel ◽  
Macromolecular Complex ◽  
Na Current ◽  
Gene Encoding ◽  
Α Subunit ◽  
Post Translational Modifications ◽  
Voltage Gated ◽  
Novel Therapeutic Strategies ◽  
And Function

The voltage-gated Na channel isoform 1.5 (NaV1.5) is the pore forming α-subunit of the voltage-gated cardiac Na channel, which is responsible for the initiation and propagation of cardiac action potentials. Mutations in the SCN5A gene encoding NaV1.5 have been linked to changes in the Na current leading to a variety of arrhythmogenic phenotypes, and alterations in the NaV1.5 expression level, Na current density, and/or gating have been observed in acquired cardiac disorders, including heart failure. The precise mechanisms underlying these abnormalities have not been fully elucidated. However, several recent studies have made it clear that NaV1.5 forms a macromolecular complex with a number of proteins that modulate its expression levels, localization, and gating and is the target of extensive post-translational modifications, which may also influence all these properties. We review here the molecular aspects of cardiac Na channel regulation and their functional consequences. In particular, we focus on the molecular and functional aspects of Na channel phosphorylation by the Ca/calmodulin-dependent protein kinase II, which is hyperactive in heart failure and has been causally linked to cardiac arrhythmia. Understanding the mechanisms of altered NaV1.5 expression and function is crucial for gaining insight into arrhythmogenesis and developing novel therapeutic strategies.

scholarly journals Zfhx3 Transcription Factor Represses the Expression of SCN5A Gene and Decreases Sodium Current Density (INa)

2021 ◽  
Vol 22 (23) ◽  
pp. 13031
Author(s):  
Marcos Rubio-Alarcón ◽  
Anabel Cámara-Checa ◽  
María Dago ◽  
Teresa Crespo-García ◽  
Paloma Nieto-Marín ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Cardiac Tissue ◽  
Sodium Current ◽  
Na Channel ◽  
Ubiquitin Protein Ligase ◽  
Endogenous Expression ◽  
Voltage Dependent ◽  
Familial Atrial Fibrillation ◽  
Cardiac Excitability ◽  
Scn5a Gene

The ZFHX3 and SCN5A genes encode the zinc finger homeobox 3 (Zfhx3) transcription factor (TF) and the human cardiac Na+ channel (Nav1.5), respectively. The effects of Zfhx3 on the expression of the Nav1.5 channel, and in cardiac excitability, are currently unknown. Additionally, we identified three Zfhx3 variants in probands diagnosed with familial atrial fibrillation (p.M1260T) and Brugada Syndrome (p.V949I and p.Q2564R). Here, we analyzed the effects of native (WT) and mutated Zfhx3 on Na+ current (INa) recorded in HL-1 cardiomyocytes. ZFHX3 mRNA can be detected in human atrial and ventricular samples. In HL-1 cardiomyocytes, transfection of Zfhx3 strongly reduced peak INa density, while the silencing of endogenous expression augmented it (from −65.9 ± 8.9 to −104.6 ± 10.8 pA/pF; n ≥ 8, p < 0.05). Zfhx3 significantly reduced the transcriptional activity of human SCN5A, PITX2, TBX5, and NKX25 minimal promoters. Consequently, the mRNA and/or protein expression levels of Nav1.5 and Tbx5 were diminished (n ≥ 6, p < 0.05). Zfhx3 also increased the expression of Nedd4-2 ubiquitin-protein ligase, enhancing Nav1.5 proteasomal degradation. p.V949I, p.M1260T, and p.Q2564R Zfhx3 produced similar effects on INa density and time- and voltage-dependent properties in WT. WT Zfhx3 inhibits INa as a result of a direct repressor effect on the SCN5A promoter, the modulation of Tbx5 increasing on the INa, and the increased expression of Nedd4-2. We propose that this TF participates in the control of cardiac excitability in human adult cardiac tissue.

scholarly journals Calmodulin Regulation of NaV1.4 Current: Role of Binding to the Carboxyl Terminus

2008 ◽  
Vol 131 (3) ◽  
pp. 197-209 ◽  
Author(s):  
Subrata Biswas ◽  
Isabelle Deschênes ◽  
Deborah DiSilvestre ◽  
Yanli Tian ◽  
Victoria L. Halperin ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Surface Membrane ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Na Channel ◽  
Na Current ◽  
Iq Motif ◽  
C Terminus ◽  
Steady State Inactivation ◽  
And Function

Calmodulin (CaM) regulates steady-state inactivation of sodium currents (NaV1.4) in skeletal muscle. Defects in Na current inactivation are associated with pathological muscle conditions such as myotonia and paralysis. The mechanisms of CaM modulation of expression and function of the Na channel are incompletely understood. A physical association between CaM and the intact C terminus of NaV1.4 has not previously been demonstrated. FRET reveals channel conformation-independent association of CaM with the C terminus of NaV1.4 (CT-NaV1.4) in mammalian cells. Mutation of the NaV1.4 CaM-binding IQ motif (NaV1.4IQ/AA) reduces cell surface expression of NaV1.4 channels and eliminates CaM modulation of gating. Truncations of the CT that include the IQ region abolish Na current. NaV1.4 channels with one CaM fused to the CT by variable length glycine linkers exhibit CaM modulation of gating only with linker lengths that allowed CaM to reach IQ region. Thus one CaM is sufficient to modulate Na current, and CaM acts as an ancillary subunit of NaV1.4 channels that binds to the CT in a conformation-independent fashion, modulating the voltage dependence of inactivation and facilitating trafficking to the surface membrane.

scholarly journals Atrial Myocyte NLRP3/CaMKII Nexus Forms a Substrate for Postoperative Atrial Fibrillation

2020 ◽  
Vol 127 (8) ◽  
pp. 1036-1055 ◽  
Author(s):  
Jordi Heijman ◽  
Azinwi Phina Muna ◽  
Tina Veleva ◽  
Cristina E. Molina ◽  
Henry Sutanto ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Patch Clamp ◽  
Protein Expression ◽  
Postoperative Atrial Fibrillation ◽  
Interleukin 1Β ◽  
Right Atrial ◽  
Open Probability ◽  
Atrial Cardiomyocytes ◽  
Increased Risk ◽  
Tissue Homogenates

Rationale: Postoperative atrial fibrillation (POAF) is a common and troublesome complication of cardiac surgery. POAF is generally believed to occur when postoperative triggers act on a preexisting vulnerable substrate, but the underlying cellular and molecular mechanisms are largely unknown. Objective: To identify cellular POAF mechanisms in right atrial samples from patients without a history of atrial fibrillation undergoing open-heart surgery. Methods and Results: Multicellular action potentials, membrane ion-currents (perforated patch-clamp), or simultaneous membrane-current (ruptured patch-clamp) and [Ca 2+ ] i -recordings in atrial cardiomyocytes, along with protein-expression levels in tissue homogenates or cardiomyocytes, were assessed in 265 atrial samples from patients without or with POAF. No indices of electrical, profibrotic, or connexin remodeling were noted in POAF, but Ca 2+ -transient amplitude was smaller, although spontaneous sarcoplasmic reticulum (SR) Ca 2+ -release events and L-type Ca 2+ -current alternans occurred more frequently. CaMKII (Ca 2+ /calmodulin-dependent protein kinase-II) protein-expression, CaMKII-dependent phosphorylation of the cardiac RyR2 (ryanodine-receptor channel type-2), and RyR2 single-channel open-probability were significantly increased in POAF. SR Ca 2+ -content was unchanged in POAF despite greater SR Ca 2+ -leak, with a trend towards increased SR Ca 2+ -ATPase activity. Patients with POAF also showed stronger expression of activated components of the NLRP3 (NACHT, LRR, and PYD domains-containing protein-3)-inflammasome system in atrial whole-tissue homogenates and cardiomyocytes. Acute application of interleukin-1β caused NLRP3-signaling activation and CaMKII-dependent RyR2/phospholamban hyperphosphorylation in an immortalized mouse atrial cardiomyocyte cell-line (HL-1-cardiomyocytes) and enhanced spontaneous SR Ca 2+ -release events in both POAF cardiomyocytes and HL-1-cardiomyocytes. Computational modeling showed that RyR2 dysfunction and increased SR Ca 2+ -uptake are sufficient to reproduce the Ca 2+ -handling phenotype and indicated an increased risk of proarrhythmic delayed afterdepolarizations in POAF subjects in response to interleukin-1β. Conclusions: Preexisting Ca 2+ -handling abnormalities and activation of NLRP3-inflammasome/CaMKII signaling are evident in atrial cardiomyocytes from patients who subsequently develop POAF. These molecular substrates sensitize cardiomyocytes to spontaneous Ca 2+ -releases and arrhythmogenic afterdepolarizations, particularly upon exposure to inflammatory mediators. Our data reveal a potential cellular and molecular substrate for this important clinical problem.

scholarly journals Aldosterone regulation of intestinal Na absorption involves SGK-mediated changes in NHE3 and Na+ pump activity

2008 ◽  
Vol 295 (5) ◽  
pp. G909-G919 ◽  
Author(s):  
Mark W. Musch ◽  
Alvaro Lucioni ◽  
Eugene B. Chang
Keyword(s):  
Protein Expression ◽  
Basolateral Membrane ◽  
Sodium Concentration ◽  
Second Phase ◽  
Multiple Time ◽  
Α Subunit ◽  
Two Phases ◽  
And Function ◽  
Induced Changes ◽  
Stimulation Of

Aldosterone-induced intestinal Na+ absorption is mediated by increased activities of apical membrane Na+/H+ exchange (aNHE3) and basolateral membrane Na+-K+-ATPase (BLM-Na+-K+-ATPase) activities. Because the processes coordinating these events were not well understood, we investigated human intestinal Caco-2BBE cells where aldosterone increases within 2–4 h of aNHE3 and α-subunit of BLM-Na+-K+-ATPase, but not total abundance of these proteins. Although aldosterone activated Akt2 and serum glucorticoid kinase-1 (SGK-1), the latter through stimulation of phosphatidylinositol 3-kinase (PI3K), only the SGK-1 pathway mediated its effects on Na+-K+-ATPase. Ouabain inhibition of the early increase in aldosterone-induced Na+-K+-ATPase activation blocked most of the apical NHE3 insertion, possibly by inhibiting Na+-K+-ATPase-induced changes in intracellular sodium concentration ([Na]i). Over the next 6–48 h, further increases in aNHE3 and BLM-Na+-K+-ATPase activity and total protein expression were observed to be largely mediated by aldosterone-activated SGK-1 pathway. Aldosterone-induced increases in NHE3 mRNA, for instance, could be inhibited by RNA silencing of SGK-1, but not Akt2. Additionally, aldosterone-induced increases in NHE3 promoter activity were blocked by silencing SGK-1 as well as pharmacological inhibition of PI3K. In conclusion, aldosterone-stimulated intestinal Na+ absorption involves two phases. The first phase involves stimulation of PI3K, which increases SGK-dependent insertion and function of BLM-Na+-K+-ATPase and subsequent increased membrane insertion of aNHE3. The latter may be caused by Na+-K+-ATPase-induced changes in [Na] or transcellular Na flux. The second phase involves SGK-dependent increases in total NHE3 and Na+-K+-ATPase protein expression and activities. The coordination of apical and BLM transporters after aldosterone stimulation is therefore a complex process that requires multiple time- and interdependent cellular processes.

scholarly journals Increased NaV1.8 expression in patients with sleep-disordered breathing induces pro-arrhythmic activity

2021 ◽  
Vol 42 (Supplement_1) ◽  
Author(s):  
S Lebek ◽  
J Rohde ◽  
P Hegner ◽  
M Tafelmeier ◽  
B Floerchinger ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Mrna Expression ◽  
Sleep Disordered Breathing ◽  
Significant Positive Correlation ◽  
Interaction Analysis ◽  
Right Atrial ◽  
Na Channel ◽  
Na Current ◽  
Positive Correlation ◽  
Disordered Breathing

Abstract Background Sleep-disordered breathing (SDB) is often associated with atrial fibrillation, but detailed mechanisms remain elusive. Interestingly, late Na current (late INa) has been shown to be increased in patients with SDB, while expression of cardiac Na channel NaV1.5 and peak Na current were decreased. Indeed, recent data demonstrated that enhanced NaV1.8-dependent late INa may also induce pro-arrhythmic activity. Purpose We tested whether Na-V1.8 expression and subsequent NaV1.8-dependent pro-arrhythmic activity are increased in patients with SDB. Methods We prospectively analysed 29 right atrial appendage biopsies of patients undergoing elective coronary artery bypass grafting. SDB was assessed using polygraphy in the preoperative night and an apnoea-hypopnea index (AHI) ≥15/h defined SDB. Micro-dissected atrial trabeculae were electrically field stimulated (at 1 Hz, 5 V for 50 ms, at 37°C) to elicit regular contractions. Trabecular arrhythmias were induced using 100 nM isoproterenol at [Ca]o of 3.5 mmol/L and pro-arrhythmic activity was scored from 0 (no arrhythmias) to 5 (salve). Sarcoplasmic reticulum Ca leak was estimated by the contractility after paused stimulation (at 2 Hz, normalized to before pause). To correlate functional and expression data for each individual patient, NaV1.8 mRNA expression was quantified in each trabeculum using qPCR. Results NaV1.8 mRNA expression was increased in patients with SDB, leading to a significant positive correlation with the severity of SDB (i.e. AHI, p=0.02, r2=0.22, Fig. 1A). Multivariate regression analysis revealed that this association was independent from age, sex, atrial fibrillation, heart failure, diabetes mellitus, and renal function (p=0.03, r2=0.35). Accordingly, selective NaV1.8 blockade with PF-01247324 (PF, 1 μM, 30 min) significantly improved post-pause contractility of isolated trabeculae from 1.69±0.31 to 2.95±0.54 in patients with SDB (p=0.001), whereas no significant improvement was observed in patients without SDB. This resulted in significant positive correlations between the PF-dependent improvement of post-pause contractility and both AHI (p=0.047, r2=0.19) and NaV1.8 mRNA expression (p=0.03, r2=0.17). Most importantly, we also observed a significant increase in arrhythmia severity in patients with SDB of 2.21±0.52 (vs. 1.00±0.49, p=0.03) that could be significantly reduced by selective NaV1.8 inhibition with PF to 0.25±0.18 (p=0.0008, Fig. 1B). In accordance, there was a significant positive correlation between arrhythmia severity and AHI (p=0.01, r2=0.28) that was abolished in the presence of PF (interaction analysis: p=0.ehab724.33141, r2=0.46). Conclusion In patients with SDB, enhanced NaV1.8 expression contribute to atrial pro-arrhythmic activity independent from comorbidities. Selective NaV1.8 inhibition may have therapeutic implications for patients with SDB. FUNDunding Acknowledgement Type of funding sources: Other. Main funding source(s): Part of the study was supported by grants from Philips Respironics (Murrysville, PA 15668) and the Medical Faculty at the University of Regensburg. Figure 1

scholarly journals The Effect of Catheter Ablation on Left Atrial Size and Function for Patients with Atrial Fibrillation: An Updated Meta-Analysis

PLoS ONE ◽  
2015 ◽  
Vol 10 (7) ◽  
pp. e0129274 ◽  
Author(s):  
Bin Xiong ◽  
Dan Li ◽  
Jianling Wang ◽  
Laxman Gyawali ◽  
Jinjin Jing ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Catheter Ablation ◽  
Left Atrial ◽  
Meta Analysis ◽  
Left Atrial Size ◽  
Atrial Size ◽  
And Function

scholarly journals Maturation of the Na,K-ATPase in the Endoplasmic Reticulum in Health and Disease

2021 ◽  
Author(s):  
Vitalii Kryvenko ◽  
Olga Vagin ◽  
Laura A. Dada ◽  
Jacob I. Sznajder ◽  
István Vadász
Keyword(s):  
Endoplasmic Reticulum ◽  
Intracellular Signaling ◽  
Loss Of Function ◽  
Α Subunit ◽  
Rate Limiting Step ◽  
Atpase Subunits ◽  
A Cell ◽  
Health And Disease ◽  
And Function ◽  
Rate Limiting

Abstract The Na,K-ATPase establishes the electrochemical gradient of cells by driving an active exchange of Na+ and K+ ions while consuming ATP. The minimal functional transporter consists of a catalytic α-subunit and a β-subunit with chaperon activity. The Na,K-ATPase also functions as a cell adhesion molecule and participates in various intracellular signaling pathways. The maturation and trafficking of the Na,K-ATPase include co- and post-translational processing of the enzyme in the endoplasmic reticulum (ER) and the Golgi apparatus and subsequent delivery to the plasma membrane (PM). The ER folding of the enzyme is considered as the rate-limiting step in the membrane delivery of the protein. It has been demonstrated that only assembled Na,K-ATPase α:β-complexes may exit the organelle, whereas unassembled, misfolded or unfolded subunits are retained in the ER and are subsequently degraded. Loss of function of the Na,K-ATPase has been associated with lung, heart, kidney and neurological disorders. Recently, it has been shown that ER dysfunction, in particular, alterations in the homeostasis of the organelle, as well as impaired ER-resident chaperone activity may impede folding of Na,K-ATPase subunits, thus decreasing the abundance and function of the enzyme at the PM. Here, we summarize our current understanding on maturation and subsequent processing of the Na,K-ATPase in the ER under physiological and pathophysiological conditions. Graphic Abstract

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