SK4 K+ Channels Regulate Sinoatrial Pacemaker and their Blockade Ameliorate Arrhythmias in CPVT2 Patient-Derived IPSC and in vivo in CASQ2 Knock-In and Knock-Out Mice

Abstract

Catecholaminergic Polymorphic Ventricular Tachychardia (CPVT) is a stressed-provoked ventricular arrhythmia triggered by diastolic intracellular calcium leak, which can lead to sudden death. While many studies have focused on ventricular tachyarrhythmia, very little is known about the pathological pacemaker of this disease. Recently, we identified the calcium-activated potassium channel SK4 as a new player involved in the pacemaker of cardiomyocytes derived from human embryonic stem cells. Here we used human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) from healthy and CPVT2 (CASQ2 D307H) patients, mouse sinoatrial node (SAN) cells as well as knock-in (CASQ2 D307H) and knock-out mice to investigate the pacemaker arrhythmogenic properties of this disease. Using TRAM-34, a selective blocker of SK4 channels, we could isolate SK4 currents in both wild-type and CPVT2-derived hiPS-CMs. Delayed afterdepolarizations in CPVT2-derived hiPS-CMs cells were observed following application of the beta-adrenergic agonist isoproterenol (Iso). Interestingly, the iso-provoked arrhythmias were markedly reduced by adding TRAM-34 (2-5 μM). Like in hiPS-CMs, we also identified TRAM34-sensitive SK4 currents in mouse SAN. Under continuous ECG recording, we found that intraperitoneal injection of the SK4 blockers TRAM 34 or clotrimazole (20 mg/kg) produced a bradycardic effect in WT, knock-in and knock-out mice, thereby increasing the PP and PR intervals. Remarkably, TRAM 34 or clotrimazole dramatically reduced the ECG arrhythmia features of knock-in and knock-out mice like ventricular tachycardia, ventricular premature contractions or bigeminy. These results suggest that SK4 Ca2+ activated K+ channels play a critical role in normal and diseased pacemaker dysfunction and notably that found in CPVT2. Our data also indicate that SK4 channel blockers could open new horizons in the management of CPVT rhythm disorders.