Brown Tashalee R, Krogh-Madsen Trine, Christini David J
Department of Physiology, Biophysics, and Systems Biology, Weill Cornell Graduate School of Medical Sciences, New York, New York; Weill Cornell/Rockefeller/Sloan-Kettering Tri-Institutional MD-PhD Program, New York, New York.
Greenberg Division of Cardiology, Weill Cornell Medicine, New York, New York.
Biophys J. 2016 Aug 23;111(4):785-797. doi: 10.1016/j.bpj.2016.06.042.
Fibroblasts play a significant role in the development of electrical and mechanical dysfunction of the heart; however, the underlying mechanisms are only partially understood. One widely studied mechanism suggests that fibroblasts produce excess extracellular matrix, resulting in collagenous septa that slow propagation, cause zig-zag conduction paths, and decouple cardiomyocytes, resulting in a substrate for cardiac arrhythmia. An emerging mechanism suggests that fibroblasts promote arrhythmogenesis through direct electrical interactions with cardiomyocytes via gap junction (GJ) channels. In the heart, three major connexin (Cx) isoforms, Cx40, Cx43, and Cx45, form GJ channels in cell-type-specific combinations. Because each Cx is characterized by a unique time- and transjunctional voltage-dependent profile, we investigated whether the electrophysiological contributions of fibroblasts would vary with the specific composition of the myocyte-fibroblast (M-F) GJ channel. Due to the challenges of systematically modifying Cxs in vitro, we coupled native cardiomyocytes with in silico fibroblast and GJ channel electrophysiology models using the dynamic-clamp technique. We found that there is a reduction in the early peak of the junctional current during the upstroke of the action potential (AP) due to GJ channel gating. However, effects on the cardiomyocyte AP morphology were similar regardless of the specific type of GJ channel (homotypic Cx43 and Cx45, and heterotypic Cx43/Cx45 and Cx45/Cx43). To illuminate effects at the tissue level, we performed multiscale simulations of M-F coupling. First, we developed a cell-specific model of our dynamic-clamp experiments and investigated changes in the underlying membrane currents during M-F coupling. Second, we performed two-dimensional tissue sheet simulations of cardiac fibrosis and incorporated GJ channels in a cell type-specific manner. We determined that although GJ channel gating reduces junctional current, it does not significantly alter conduction velocity during cardiac fibrosis relative to static GJ coupling. These findings shed more light on the complex electrophysiological interplay between cardiac fibroblasts and myocytes.
成纤维细胞在心脏电和机械功能障碍的发展中起重要作用；然而，其潜在机制仅得到部分理解。一种被广泛研究的机制表明，成纤维细胞产生过量的细胞外基质，导致胶原间隔，减缓电信号传播，造成曲折的传导路径，并使心肌细胞解耦联，从而形成心律失常的基质。一种新出现的机制表明，成纤维细胞通过间隙连接（GJ）通道与心肌细胞直接进行电相互作用来促进心律失常的发生。在心脏中，三种主要的连接蛋白（Cx）亚型，即Cx40、Cx43和Cx45，以细胞类型特异性组合形成GJ通道。由于在体外系统修饰Cx存在挑战，我们使用动态钳技术将天然心肌细胞与计算机模拟的成纤维细胞和GJ通道电生理模型相结合。我们发现，由于GJ通道门控，动作电位（AP）上升支期间的连接电流早期峰值降低。然而，无论GJ通道的具体类型（同型Cx43和Cx45，以及异型Cx43/Cx45和Cx45/Cx43）如何，对心肌细胞AP形态的影响都是相似的。为了阐明组织水平的影响，我们进行了心肌-成纤维细胞（M-F）耦联的多尺度模拟。首先，我们建立了动态钳实验的细胞特异性模型，并研究了M-F耦联过程中基础膜电流的变化。其次，我们进行了心脏纤维化的二维组织片模拟，并以细胞类型特异性方式纳入GJ通道。我们确定，尽管GJ通道门控会降低连接电流，但相对于静态GJ耦联，它在心脏纤维化期间不会显著改变传导速度。这些发现为心脏成纤维细胞和心肌细胞之间复杂的电生理相互作用提供了更多的线索。
