Functional Analysis of SCN5A Genetic Variants Associated with Brugada Syndrome.

BACKGROUND: Brugada syndrome (BrS) is a rare inherited cardiac arrhythmia with increased risk of sudden cardiac death. Mutations in gene SCN5A, which encodes the α-subunit of cardiac voltage-gated sodium channel NaV1.5, have been identified in over 20% of patients with BrS. However, only a small fraction of NaV1.5 variants, which are associated with BrS, are characterized in electrophysiological experiments. RESULTS: Here we explored variants V281A and L1582P, which were found in our patients with BrS, and variants F543L and K1419E, which are reportedly associated with BrS. Heterologous expression of the variants in CHO-K1 cells and the Western blot analysis demonstrated that each variant appeared at the cell surface. We further measured sodium current in the whole-cell voltage clamp configuration. Variant F543L produced robust sodium current with a hyperpolarizing shift in the voltage dependence of steady-state fast inactivation. Other variants did not produce detectable sodium currents, indicating a complete loss of function. In a recent cryoEM structure of the hNaV1.5 channel, residues V281, K1419, and L1582 are in close contacts with residues whose mutations are reportedly associated with BrS, indicating functional importance of respective contacts. CONCLUSIONS: Our results support the notion that loss of function of NaV1.5 or decrease of the channel activity is involved in the pathogenesis of BrS.

SGLT2 Inhibitor Empagliflozin Modulates Ion Channels in Adult Zebrafish Heart.

Empagliflozin, an inhibitor of sodium-glucose co-transporter 2 (iSGLT2), improves cardiovascular outcomes in patients with and without diabetes and possesses an antiarrhythmic activity. However, the mechanisms of these protective effects have not been fully elucidated. This study aimed to explore the impact of empagliflozin on ion channel activity and electrophysiological characteristics in the ventricular myocardium. The main cardiac ionic currents (INa, ICaL, ICaT, IKr, IKs) and action potentials (APs) were studied in zebrafish. Whole-cell currents were measured using the patch clamp method in the isolated ventricular cardiomyocytes. The conventional sharp glass microelectrode technique was applied for the recording of APs from the ventricular myocardium of the excised heart. Empagliflozin pretreatment compared to the control group enhanced potassium IKr step current density in the range of testing potentials from 0 to +30 mV, IKr tail current density in the range of testing potentials from +10 to +70 mV, and IKs current density in the range of testing potentials from -10 to +20 mV. Moreover, in the ventricular myocardium, empagliflozin pretreatment shortened AP duration APD as shown by reduced APD50 and APD90. Empagliflozin had no influence on sodium (INa) and L- and T-type calcium currents (ICaL and ICaT) in zebrafish ventricular cardiomyocytes. Thus, we conclude that empagliflozin increases the rapid and slow components of delayed rectifier K+ current (IKr and IKs). This mechanism could be favorable for cardiac protection.