Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg, Bad Krozingen, Medical Center - University of Freiburg, Germany; Faculty of Medicine, University of Freiburg, Germany.
CNRS University Cote d'Azur laboratory Institut Biology Valrose, Nice, France.
J Mol Cell Cardiol. 2021 Sep;158:49-62. doi: 10.1016/j.yjmcc.2021.05.002. Epub 2021 May 8.
Atrial Fibrillation (AF) is an arrhythmia of increasing prevalence in the aging populations of developed countries. One of the important indicators of AF is sustained atrial dilatation, highlighting the importance of mechanical overload in the pathophysiology of AF. The mechanisms by which atrial cells, including fibroblasts, sense and react to changing mechanical forces, are not fully elucidated. Here, we characterise stretch-activated ion channels (SAC) in human atrial fibroblasts and changes in SAC- presence and activity associated with AF.
Using primary cultures of human atrial fibroblasts, isolated from patients in sinus rhythm or sustained AF, we combine electrophysiological, molecular and pharmacological tools to identify SAC. Two electrophysiological SAC- signatures were detected, indicative of cation-nonselective and potassium-selective channels. Using siRNA-mediated knockdown, we identified the cation-nonselective SAC as Piezo1. Biophysical properties of the potassium-selective channel, its sensitivity to calcium, paxilline or iberiotoxin (blockers), and NS11021 (activator), indicated presence of calcium-dependent 'big potassium channels' (BK). In cells from AF patients, Piezo1 activity and mRNA expression levels were higher than in cells from sinus rhythm patients, while BK activity (but not expression) was downregulated. Both Piezo1-knockdown and removal of extracellular calcium from the patch pipette resulted in a significant reduction of BK current during stretch. No co-immunoprecipitation of Piezo1 and BK was detected.
Human atrial fibroblasts contain at least two types of ion channels that are activated during stretch: Piezo1 and BK. While Piezo1 is directly stretch-activated, the increase in BK activity during mechanical stimulation appears to be mainly secondary to calcium influx via SAC such as Piezo1. During sustained AF, Piezo1 is increased, while BK activity is reduced, highlighting differential regulation of both channels. Our data support the presence and interplay of Piezo1 and BK in human atrial fibroblasts in the absence of physical links between the two channel proteins.
心房颤动（AF）是发达国家老龄化人口中发病率不断上升的心律失常。AF 的一个重要指标是持续性心房扩张，这突出了机械超负荷在 AF 病理生理学中的重要性。心房细胞（包括成纤维细胞）感知和对不断变化的机械力作出反应的机制尚未完全阐明。在这里，我们描述了在人类心房成纤维细胞中拉伸激活的离子通道（SAC）以及与 AF 相关的 SAC 存在和活性变化。
我们使用从窦性心律或持续性 AF 患者中分离的原代培养的人心房成纤维细胞，结合电生理学、分子和药理学工具来鉴定 SAC。检测到两种电生理学 SAC 特征，表明存在阳离子非选择性和钾选择性通道。使用 siRNA 介导的敲低，我们鉴定出阳离子非选择性 SAC 为 Piezo1。钾选择性通道的生物物理特性、对钙、paxilline 或 iberiotoxin（阻断剂）的敏感性以及 NS11021（激活剂）表明存在钙依赖性“大钾通道”（BK）。在来自 AF 患者的细胞中，Piezo1 活性和 mRNA 表达水平高于来自窦性心律患者的细胞，而 BK 活性（而非表达）下调。Piezo1 敲低和从贴壁电极中去除细胞外钙都会导致在拉伸期间 BK 电流的显著减少。未检测到 Piezo1 和 BK 的共免疫沉淀。
人类心房成纤维细胞中至少含有两种在拉伸过程中被激活的离子通道：Piezo1 和 BK。虽然 Piezo1 是直接拉伸激活的，但机械刺激期间 BK 活性的增加似乎主要是由于 Piezo1 等 SAC 引起的钙内流引起的。在持续性 AF 中，Piezo1 增加，而 BK 活性降低，突出了两种通道的差异调节。我们的数据支持在不存在两种通道蛋白之间物理联系的情况下，Piezo1 和 BK 存在于人类心房成纤维细胞中，并相互作用。
