Dept. of Physiology, University of Bern, Bühlplatz 5, CH-3012 Bern, Switzerland.
Circ Res. 2011 Oct 28;109(10):1120-31. doi: 10.1161/CIRCRESAHA.111.244798. Epub 2011 Sep 15.
Myofibroblasts typically appear in the myocardium after insults to the heart like mechanical overload and infarction. Apart from contributing to fibrotic remodeling, myofibroblasts induce arrhythmogenic slow conduction and ectopic activity in cardiomyocytes after establishment of heterocellular electrotonic coupling in vitro. So far, it is not known whether α-smooth muscle actin (α-SMA) containing stress fibers, the cytoskeletal components that set myofibroblasts apart from resident fibroblasts, are essential for myofibroblasts to develop arrhythmogenic interactions with cardiomyocytes.
We investigated whether pharmacological ablation of α-SMA containing stress fibers by actin-targeting drugs affects arrhythmogenic myofibroblast-cardiomyocyte cross-talk.
Experiments were performed with patterned growth cell cultures of neonatal rat ventricular cardiomyocytes coated with cardiac myofibroblasts. The preparations exhibited slow conduction and ectopic activity under control conditions. Exposure to actin-targeting drugs (Cytochalasin D, Latrunculin B, Jasplakinolide) for 24 hours led to disruption of α-SMA containing stress fibers. In parallel, conduction velocities increased dose-dependently to values indistinguishable from cardiomyocyte-only preparations and ectopic activity measured continuously over 24 hours was completely suppressed. Mechanistically, antiarrhythmic effects were due to myofibroblast hyperpolarization (Cytochalasin D, Latrunculin B) and disruption of heterocellular gap junctional coupling (Jasplakinolide), which caused normalization of membrane polarization of adjacent cardiomyocytes.
The results suggest that α-SMA containing stress fibers importantly contribute to myofibroblast arrhythmogeneicity. After ablation of this cytoskeletal component, cells lose their arrhythmic effects on cardiomyocytes, even if heterocellular electrotonic coupling is sustained. The findings identify α-SMA containing stress fibers as a potential future target of antiarrhythmic therapy in hearts undergoing structural remodeling.
心肌细胞受到机械过载和梗塞等心脏损伤后，通常会出现肌成纤维细胞。除了促进纤维化重塑外，肌成纤维细胞在体外建立异质细胞电偶联后，还会导致心肌细胞产生致心律失常的缓慢传导和异位活动。到目前为止，尚不清楚是否含有应力纤维的α-平滑肌肌动蛋白（α-SMA），即区分肌成纤维细胞和驻留成纤维细胞的细胞骨架成分，对于肌成纤维细胞与心肌细胞发生致心律失常相互作用是否是必需的。
我们研究了肌成纤维细胞中含应力纤维的α-SMA 的药理学消融是否会影响致心律失常的肌成纤维细胞-心肌细胞交叉对话。
采用涂覆心肌成纤维细胞的新生大鼠心室心肌细胞模式化生长细胞培养进行实验。在对照条件下，这些制备物表现出缓慢的传导和异位活动。暴露于肌动蛋白靶向药物（细胞松弛素 D、拉曲库林 B、jasplakinolide）24 小时可导致含应力纤维的α-SMA 断裂。同时，传导速度呈剂量依赖性增加，与仅心肌细胞制备物的值无区别，并且连续 24 小时测量的异位活动完全被抑制。从机制上讲，抗心律失常作用是由于肌成纤维细胞超极化（细胞松弛素 D、拉曲库林 B）和异质细胞缝隙连接偶联的破坏（jasplakinolide），这导致相邻心肌细胞的膜极化正常化。
结果表明，含应力纤维的α-SMA 对肌成纤维细胞的致心律失常性有重要贡献。消融这种细胞骨架成分后，即使维持异质细胞电偶联，细胞也会失去对心肌细胞的致心律失常作用。这些发现将含应力纤维的α-SMA 确定为正在进行结构重塑的心脏中抗心律失常治疗的潜在未来靶点。
