Rationale:: The cardiac sodium channel Na _v 1.5 plays a key role in excitability and conduction. The 3 last residues of Na _v 1.5 (Ser-Ile-Val) constitute a PDZ-domain binding motif that interacts with the syntrophin–dystrophin complex. As dystrophin is absent at the intercalated discs, Na _v 1.5 could potentially interact with other, yet unknown, proteins at this site. Objective:: The aim of this study was to determine whether Na _v 1.5 is part of distinct regulatory complexes at lateral membranes and intercalated discs. Methods and Results:: Immunostaining experiments demonstrated that Na _v 1.5 localizes at lateral membranes of cardiomyocytes with dystrophin and syntrophin. Optical measurements on isolated dystrophin-deficient mdx hearts revealed significantly reduced conduction velocity, accompanied by strong reduction of Na _v 1.5 at lateral membranes of mdx cardiomyocytes. Pull-down experiments revealed that the MAGUK protein SAP97 also interacts with the SIV motif of Na _v 1.5, an interaction specific for SAP97 as no pull-down could be detected with other cardiac MAGUK proteins (PSD95 or ZO-1). Furthermore, immunostainings showed that Na _v 1.5 and SAP97 are both localized at intercalated discs. Silencing of SAP97 expression in HEK293 and rat cardiomyocytes resulted in reduced sodium current ( I _Na ) measured by patch-clamp. The I _Na generated by Na _v 1.5 channels lacking the SIV motif was also reduced. Finally, surface expression of Na _v 1.5 was decreased in silenced cells, as well as in cells transfected with SIV-truncated channels. Conclusions:: These data support a model with at least 2 coexisting pools of Na _v 1.5 channels in cardiomyocytes: one targeted at lateral membranes by the syntrophin-dystrophin complex, and one at intercalated discs by SAP97.

Brugada syndrome (BrS) is characterized by arrhythmias leading to sudden cardiac death. BrS is caused, in part, by mutations in the SCN5A gene, which encodes the sodium channel alpha-subunit Na_v1.5. Here, we aimed to characterize the biophysical properties and consequences of a novel BrS SCN5A mutation. SCN5A was screened for mutations in a male patient with type-1 BrS pattern ECG. Wild-type (WT) and mutant Na_v1.5 channels were expressed in HEK293 cells. Sodium currents (I_Na) were analysed using the whole-cell patch-clamp technique at 37°C. The electrophysiological effects of the mutation were simulated using the Luo-Rudy model, into which the transient outward current (I_to) was incorporated. A new mutation (C1850S) was identified in the Na_v1.5 C-terminal domain. In HEK293 cells, mutant I_Na density was decreased by 62% at −20 mV. Inactivation of mutant I_Na was accelerated in a voltage-dependent manner and the steady-state inactivation curve was shifted by 11.6 mV towards negative potentials. No change was observed regarding activation characteristics. Altogether, these biophysical alterations decreased the availability of I_Na. In the simulations, the I_to density necessary to precipitate repolarization differed minimally between the two genotypes. In contrast, the mutation greatly affected conduction across a structural heterogeneity and precipitated conduction block. Our data confirm that mutations of the C-terminal domain of Na_v1.5 alter the inactivation of the channel and support the notion that conduction alterations may play a significant role in the pathogenesis of BrS.

Background: Mutations in SCN4A may lead to myotonia. Methods: Presentation of a large family with myotonia, including molecular studies and patch clamp experiments using human embryonic kidney 293 cells expressing wild-type and mutated channels. Results: In a large family with historic data on seven generations and a clear phenotype, including myotonia at movement onset, with worsening by cold temperature, pregnancy, mental stress, and especially after rest after intense physical activity, but without weakness, the phenotype was linked with the muscle sodium channel gene (SCN4A) locus, in which a novel p.I141V mutation was found. This modification is located within the first transmembrane segment of domain I of the Na_v1.4 α subunit, a region where no mutation has been reported so far. Patch clamp experiments revealed a mutation-induced hyperpolarizing shift (−12.9 mV) of the voltage dependence of activation, leading to a significant increase (approximately twofold) of the window current amplitude. In addition, the mutation shifted the voltage dependence of slow inactivation by −8.7 mV and accelerated the entry to this state. Conclusions: We propose that the gain-of-function alteration in activation leads to the observed myotonic phenotype, whereas the enhanced slow inactivation may prevent depolarization-induced paralysis.

A patient with an SCN5A p.W822X nonsense mutation, localized in the transmembrane region DII-S4 of the Na _v 1.5 sodium channel and leading to a non-expression of the mutant allele, was prescribed the selective serotonin reuptake inhibitor (SSRI) fluvoxamine (Floxyfral ^® ), 100 mg per day. His normal baseline ECG changed to a characteristic Brugada-Type-1-ECG pattern. To investigate whether fluvoxamine may reduce the cardiac sodium current, the effect of this drug was studied on the wild-type voltage-gated cardiac sodium channel Na _v 1.5 stably expressed in HEK293 cells. Patch-clamp recording showed a 50% inhibition of the current at a concentration of 57.3 µM. In our patient, no arrhythmia occurred but the proarrhythmic potential of SSRI in patients with SCN5A mutations cannot be excluded. Therefore, we advise 12-lead ECG control after administering SSRI in these patients.

In the recent years, an increased use of marginal donors and grafts and a growing prevalence of peripheral arterial disease in the recipients have been observed. Meanwhile, the open surgical technique for kidney transplantation has not changed. The aim of this study is to analyze all surgical complications occurring in the first year after kidney transplant and to determine potential predictive risk factors. Data of the 399 patients who underwent kidney transplant in our University Hospital between January 2006 and December 2015 were retrospectively reviewed. The primary endpoint was the overall rate of vascular, parietal and urological complications at 1 year following kidney transplantation. The secondary outcomes were graft and patient' survival rates, and the identification of predictive factors of the surgical complications. 24% of patients developed 134 complications. Vascular complication represented 39% of all complications and resulted in 9 graft losses. Parietal and urological complications represented 46-15% of all complications, respectively, No parietal or urological complications were associated with graft loss. 5 patients died during the 1^st year, none of these cases was associated with graft loss. The graft survival rate reached 96% at 1 year, including patients still alive. The occurrence of surgical complication was associated with reduced graft survival at 1 year. Using a multivariate analysis, 4 predictive factors were identified: age, deceased donor, operative time and dyslipidemia. Surgical complications after kidney transplantation remained frequent and age, deceased kidney donors, and operative time were identified as risk factors. As vascular complications were a major cause of early graft loss, efforts should aim to reduce their occurrence to increase graft survival.