Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio; Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia.
Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio; Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
Biophys J. 2020 Jun 2;118(11):2829-2843. doi: 10.1016/j.bpj.2020.04.014. Epub 2020 Apr 21.
In cardiac myocytes, action potentials are initiated by an influx of sodium (Na) ions via voltage-gated Na channels. Na channel gain of function (GOF), arising in both inherited conditions associated with mutation in the gene encoding the Na channel and acquired conditions associated with heart failure, ischemia, and atrial fibrillation, enhance Na influx, generating a late Na current that prolongs action potential duration (APD) and triggering proarrhythmic early afterdepolarizations (EADs). Recent studies have shown that Na channels are highly clustered at the myocyte intercalated disk, facilitating formation of Na nanodomains in the intercellular cleft between cells. Simulations from our group have recently predicted that narrowing the width of the intercellular cleft can suppress APD prolongation and EADs in the presence of Na channel mutations because of increased intercellular cleft Na ion depletion. In this study, we investigate the effects of modulating multiple extracellular spaces, specifically the intercellular cleft and bulk interstitial space, in a novel computational model and experimentally via osmotic agents albumin, dextran 70, and mannitol. We perform optical mapping and transmission electron microscopy in a drug-induced (sea anemone toxin, ATXII) Na channel GOF isolated heart model and modulate extracellular spaces via osmotic agents. Single-cell patch-clamp experiments confirmed that the osmotic agents individually do not enhance late Na current. Both experiments and simulations are consistent with the conclusion that intercellular cleft narrowing or expansion regulates APD prolongation; in contrast, modulating the bulk interstitial space has negligible effects on repolarization. Thus, we predict that intercellular cleft Na nanodomain formation and collapse critically regulates cardiac repolarization in the setting of Na channel GOF.
在心肌细胞中，动作电位由电压门控钠离子通道（Na 通道）内流引发。Na 通道功能获得性突变（GOF）既存在于与编码 Na 通道的基因突变相关的遗传性疾病中，也存在于与心力衰竭、缺血和心房颤动相关的获得性疾病中，这种突变增强了 Na 内流，产生晚期 Na 电流，延长动作电位时程（APD），并引发致心律失常性早期后除极（EAD）。最近的研究表明，Na 通道在心肌细胞闰盘处高度聚集，有利于细胞间缝隙中形成 Na 纳米区。我们小组最近的模拟预测，由于细胞间缝隙中 Na 离子耗竭增加，缩小细胞间缝隙的宽度可以抑制 Na 通道突变时 APD 的延长和 EAD。在这项研究中，我们通过新型计算模型和渗透压剂白蛋白、葡聚糖 70 和甘露醇在药物诱导（海葵毒素 ATXII）Na 通道 GOF 分离心脏模型中进行实验，研究了调节多个细胞外空间的影响，特别是细胞间缝隙和间质空间。我们进行了光学映射和透射电子显微镜检查，并在药物诱导的 Na 通道 GOF 分离心脏模型中通过渗透压剂调节细胞外空间。单细胞膜片钳实验证实，渗透压剂单独使用不会增强晚期 Na 电流。实验和模拟的结果都一致表明，细胞间缝隙的变窄或扩张调节 APD 的延长；相反，调节间质空间对复极化几乎没有影响。因此，我们预测在 Na 通道 GOF 中，细胞间缝隙 Na 纳米区的形成和崩溃对心脏复极的调节起着关键作用。
