Veress Roland, Terentyeva Radmila, Belevych Andriy E, Perger Fruzsina, Nichtova Zuzana, Pokrass Anastasia, Cheng Yujia, Chorna Snizhana, Deschenes Isabelle, Gyorke Sandor, Knollmann Bjorn, Clements Richard T, Singh Harpreet, Liu Bin, Csordas Gyorgy, Hamilton Shanna, Terentyev Dmitry
Department of Physiology and Cell Biology, The Ohio State University, Columbus (R.V., R.T., A.E.B., F.P., A.P., S.C., I.D., S.G., H.S., D.T.).
Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus (R.V., R.T., A.E.B., F.P., A.P., S.C., I.D., S.G., H.S., D.T.).
Circ Res. 2025 May 29. doi: 10.1161/CIRCRESAHA.124.325477.
Sarcolemmal small conductance Ca-activated K channels have the unique capacity to translate intracellular Ca signal into repolarization, while mitochondrial SK channels can link Ca cycling to mitochondrial function. We hypothesize that pharmacological enhancement of SK channels can be protective against malignant cardiac arrhythmias associated with disturbances in Ca handling machinery.
A mouse CASQ2 KO (calsequestrin type 2 knockout) model of catecholaminergic polymorphic ventricular tachycardia (CPVT) was used for in vivo ECG recordings and for cell electrophysiology, Ca, and reactive oxygen species imaging in isolated ventricular myocytes (VMs).
Bidirectional and polymorphic ventricular tachycardias in CASQ2 KO mice induced by stress challenge (epinephrine+caffeine cocktail) were attenuated by injection of NS309, a specific SK channel enhancer. Voltage-clamp experiments in isolated VMs treated with β-adrenergic agonist isoproterenol showed a reduction of sarcolemmal SK channel current (I) density in CPVT VMs. Application of NS309 to CPVT VMs increased I. Current-clamp experiments demonstrated a significant reduction of arrhythmogenic delayed afterdepolarizations and spontaneous Ca waves in isoproterenol-challenged CPVT VMs pretreated with NS309. Importantly, subsequent application of membrane-impermeable SK channel inhibitor apamin did not reverse the protective effects of NS309, suggesting important roles of mitochondrial SK channels in intracellular Ca handling rescue. SK channel enhancement reversed the increased rate of reactive oxygen species production by mitochondria in CPVT VMs. It also reversed increased cardiac RyR2 (ryanodine receptor 2) oxidation measured in samples from CPVT hearts of the animals after the stress challenge. Electron microscopy studies showed a significant widening of mitochondria cristae in the ventricular tissue from CPVT mice, which led to a decrease in quaternary supercomplexes of electron transport chain, resulting in impairment of ATP production in VMs under β-adrenergic stimulation. Application of NS309 facilitated cristae flattening in CPVT ventricular tissue and restored supercomplexes and ATP production in VMs from diseased animals.
Sarcolemmal SK channel enhancement reduces arrhythmic potential by restoring repolarization force in CPVT VMs. Activation of mitochondrial SK channels attenuates mitochondria structural changes in CPVT, restoring more efficient electron transport chain assembly into supercomplexes and reducing mito-reactive oxygen species production. This decreases RyR2 oxidation and thus channel activity, reducing spontaneous Ca waves underlying arrhythmogenic delayed afterdepolarizations.
肌膜小电导钙激活钾通道具有将细胞内钙信号转化为复极化的独特能力，而线粒体SK通道可将钙循环与线粒体功能联系起来。我们推测，药理学增强SK通道可预防与钙处理机制紊乱相关的恶性心律失常。
采用儿茶酚胺能多形性室性心动过速（CPVT）的小鼠CASQ2基因敲除（肌集钙蛋白2型敲除）模型进行体内心电图记录，并对分离的心室肌细胞（VMs）进行细胞电生理学、钙及活性氧成像。
应激刺激（肾上腺素+咖啡因鸡尾酒）诱导的CASQ2基因敲除小鼠的双向和多形性室性心动过速，通过注射特异性SK通道增强剂NS309得以减轻。用β-肾上腺素能激动剂异丙肾上腺素处理的分离VMs的电压钳实验显示，CPVT VMs中肌膜SK通道电流（I）密度降低。将NS309应用于CPVT VMs可增加I。电流钳实验表明，在用NS309预处理的异丙肾上腺素刺激的CPVT VMs中，致心律失常的延迟后去极化和自发钙波显著减少。重要的是，随后应用膜不可渗透的SK通道抑制剂蜂毒明肽并不能逆转NS309的保护作用，提示线粒体SK通道在细胞内钙处理挽救中起重要作用。SK通道增强可逆转CPVT VMs中线粒体活性氧产生速率的增加。它还逆转了应激刺激后动物CPVT心脏样本中测得的心脏兰尼碱受体2（RyR2）氧化增加。电子显微镜研究显示，CPVT小鼠心室组织中的线粒体嵴显著增宽，这导致电子传递链四级超复合物减少，从而导致β-肾上腺素能刺激下VMs中ATP生成受损。应用NS309可促进CPVT心室组织中的嵴变平，并恢复患病动物VMs中的超复合物和ATP生成。
肌膜SK通道增强通过恢复CPVT VMs中的复极化力来降低心律失常的可能性。线粒体SK通道的激活可减轻CPVT中线粒体的结构变化，恢复更有效的电子传递链组装成超复合物，并减少线粒体活性氧的产生。这减少了RyR2氧化，从而降低通道活性，减少致心律失常的延迟后去极化背后的自发钙波。
