Aphysiomic approach to evaluate the role of mechano-electrical feedback in arrhythmia

我们使用基于碳纤维的拉伸装置结合电压敏感染料的同步荧光测量来评估单个心肌细胞膜电位对单轴拉伸的响应。为了实现无运动伪影的膜电位的定量估计，我们采用了比率测量技术。肌细胞的膜电位对拉伸的反应是幅度依赖的，当拉伸超过细胞长度的20%时，我们观察到动作电位的发展。在平台期施加的牵张延长了动作电位，Gd是拉伸激活通道的非选择性阻滞剂，它取消了这种反应。我们还发现，膜电位的响应依赖于拉伸速度，这表明连接细胞表面和通道的链接具有粘弹性性质。实验溶液中离子的置换改变了膜电位的响应，从这些结果我们认为，在小幅度拉伸时，Ca~(2+)是主要的载流子，而在较大幅度拉伸时，Na~+起主导作用。此外，横向应用焦点压痕可引起细胞内钙离子浓度的局部升高。最后，我们将这些特性融入到所提出的拉伸激活离子通道的数学模型中，建立了非均质结构的室壁模型。该模型能成功复制牵张性心律失常。这些研究结果将有助于我们理解在异常负荷条件下心脏受到拉伸的疾病状态下发生心律失常的机制。

We evaluated the response of membrane potential to the uni-axial stretch in the single cardiomyocytes using the carbon-fiber based stretching device coupled with the simultaneous fluorescence measurement from the voltage sensitive dye. To achieve the quantitative estimation of membrane potential without the motion artifact, we adopted the ratiometry technique. Membrane potential of the myocytes responded to the stretch in an amplitude dependent manner and, with a large stretch exceeding 20% of the cell length, we observed the development of the action potential. The stretch applied during the plateau phase prolonged the action potential Administration of gadolinium, a non-selective blocker of stretch-activated channel, abolished such responses. We also found that the responses of membrane potential were dependent on the speed of stretch indicating that the visco-elastic nature of the link connecting cell surface and channels. Replacement of ions in the experimental solutions changed the membrane potential response and from these results, we considered that the Ca^2+ is the major charge carrier for the stretch of small amplitude, while the Na^+ dominates the response when the larger stretch is applied. In addition, focal indentation applied transversely invoked a local rise in intracellular Ca^2+ concentration. Finally, we incorporated such characteristics into the proposed mathematical model of the stretch-activated ion channel and developed a ventricular wall model of heterogeneous structure. The model could successfully reproduce the stretch-induce arrhythmia. Such findings obtained in this study will contribute to our understanding of the mechanisms of arrhythmia in diseased condition in which heart is subjected to stretch under abnormal loading conditions.