Coupling of Cardiac Electrical Activity Over Extended Distances by Fibroblasts of Cardiac Origin

Abstract

Abstract-Roughly half of the cells of the heart consist of nonmyocardial cells, with fibroblasts representing the predominant cell type. It is well established that individual cardiomyocytes and fibroblasts in culture establish gap junctional communication at the single cell level (short-range interaction). However, it is not known whether such coupling permits activation of cardiac tissue over extended distances (long-range interaction). Long-range interactions may be responsible for electrical synchronization of donor and recipient tissue after heart transplantation and may play a role in arrhythmogenesis. This question was investigated using a novel heterocellular culture model with strands of cardiomyocytes interrupted by cardiac fibroblasts over defined distances. With use of optical recording techniques, it could be shown that impulse propagation along fibroblast inserts was successful over distances up to 300 m and was characterized by length-dependent local propagation delays ranging from 11 to 68 ms (apparent local "conduction velocities" 4.6Ϯ1.8 mm/s, nϭ23). Involvement of mechanical stretch in this phenomenon was excluded by showing that inserts consisting of communication-deficient HeLa cells were incapable of supporting propagation. In contrast, HeLa cells expressing connexin43 permitted impulse conduction over distances as long as 600 m. Immunocytochemistry showed that fibroblasts and cardiomyocytes expressed connexin43 and connexin45, whereas connexin40 was absent. These results illustrate that fibroblasts of cardiac origin are capable of synchronizing electrical activity of multicellular cardiac tissue over extended distances through electrotonic interactions. This synchronization is accompanied by extremely large local conduction delays, which might contribute to the generation of arrhythmias in fibrotic hearts.

Cardiac cell therapy in vitro: reproducible assays for comparing the efficacy of different donor cells [Cellular/Tissue Engineering]

“…Unlike wild-type cells, genetically modified cells were able to propagate impulses over the 330-μm long inserts within cardiac strands. The results obtained are consistent with studies on wildtype and genetically modified HeLa cells by Gaudesius et al [19].…”

“…In particular, we optically mapped at a spatial resolution of 37.5 μm (i.e., subcardiomyocyte length) the propagation of calcium waves in micropatterned strands composed only of cardiomyocytes (as a control) and strands containing donor cell inserts made of skeletal myoblasts, MSCs, wild-type or genetically modified HEK-293 cells, or ES-CMs. Similar to studies by others [19], [28], positions of optical channels were overlaid on a phase contrast image of the strand, allowing the monitoring of impulse propagation along the strand by viewing impulse traces in successive channels. Importantly, the use of a pseudo onedimensional geometry circumvented potential ambiguities in the pattern of electrical propagation, a situation occasionally encountered in two-dimensional and, in particular, threedimensional tissue settings.…”

Neonatal rat cardiac fibroblasts express three types of voltage-gated K+ channels: regulation of a transient outward current by protein kinase C

“…When plated in primary culture, cardiac fibroblasts form physical interactions with cardiac myocytes through establishment of gap-junctional channels (6,8,14). With the use of a heterocellular culture model, it was established that fibroblasts are capable of relaying electrical excitation over distances as long as 300 m between strands of cardiac myocytes (14).…”

Fibroblasts modulate cardiomyocyte excitability: implications for cardiac gene therapy

“…8 More recently in a heterocellular culture system, cardiac fibroblasts were found to couple cardiomyocyte electrical activity across distances up to 300 mm. 9 In vivo demonstration of this type of electrical propagation in heterologously coupled cells is, however, lacking.…”