Cellular coupling in the heart

Description Fibroblasts in scar tissue elicit myocyte excitation and promote arrhythmia in mouse hearts Traditionally, cardiac electrophysiology has focused on myocytes—the heart muscle cells that generate action potentials and are electrically excitable. Nonmyocytes within the heart are often considered barriers to action potential propagation. Typically defined as extracellular matrix–producing cells, cardiac fibroblasts are one of the largest nonmyocyte cardiac populations. However, they have been recognized to be important for maintaining normal cardiac function and for mediating cardiac remodeling during pathology, when their number substantially increases (1). The presence of electrical coupling between fibroblasts and myocytes has been established in vitro and more recently demonstrated in situ (2–4). But definitive in vivo evidence has been lacking. On page 1480 of this issue, Wang et al. (5) report that fibroblasts and myocytes are electrically coupled in living mice. This finding could transform the understanding of cardiac connectivity and arrhythmogenesis, with profound implications for the management of heart disease patients.