Abstract 12861: Adjoining Myofibroblasts Disrupt Impulse Propagation of Myocardial Tissue via Connexin 43-Mediated Heterocellular Gap Junctional Coupling

Abstract

Introduction: The composite population of myofibroblasts (MFBs) and cardiomyocytes (CMCs) is known to alter impulse conduction in the heart. A previous study reported that structural disruption between cardiomyocytes by fibrosis or myofibroblast proliferation causes conduction delay due to insulating or reducing the intercellular current. However, it is unknown whether and how the conduction is altered when the myocardial tissue faces adjoining with MFB-rich granulation tissue, like, e.g. , the border zone of myocardial infarcts during infarct healing. Objectives: To clarify the influence of heterocellular gap-junctional coupling between CMCs and MFBs by calcium imaging in an injured myocardial tissue-mimicking model in which CMCs connect with MFBs via microporous membranes. Methods: Fluo-8 fluorescence patterns of impulse propagation were spatiotemporally imaged (27 x 18.9 mm, 333 frames/s, 32 °C) in neonatal rat CMC monolayers cultured on the upper sides of the Boyden chamber (pore diameter, 8 μm) of which MFB monolayer was co-cultured on the reverse sides (CMC-MFB group). For comparison, CMC monolayers were cultured on both membrane sides (CMC-CMC group). Results: During consecutive pacing at 1 - 4 Hz, CMC monolayers showed concentric propagation from the pacing site with slower conduction velocity (CV) and more irregular wavefronts in a frequency-dependent manner. The conduction slowing and its non-uniformity were more remarkable in the CMC-MFB group than in the CMC-CMC group. We confirmed the gap junction coupling between the upper CMC and lower MFB layers using co-immunostaining and calcein staining. Heptanol, gap junction inhibiter, inhibited calcein dye transfer from the upper CMC layer to the lower MFB layer. The knockdown of Cx43 in MFBs on the reverse layer improved the delay of CV and non-uniformity in the CMC-MFB group. Conclusions: In this study, we clarified the electric association between adjoining MFBs and CMCs. Our observations suggest that adjoining MFBs slow down conduction velocity and disrupt conduction uniformity on CMCs via Cx43-mediated heterocellular gap-junctional coupling between CMCs and MFBs.