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Open AccessArticle

Real-Time In Vivo Imaging of Mouse Left Ventricle Reveals Fluctuating Movements of the Intercalated Discs

1
Department of Cell Physiology, The Jikei University School of Medicine, Tokyo 105-8461, Japan
2
Technical Division, School of Science, The University of Tokyo, Tokyo 113-0033, Japan
3
Department of Anesthesiology, The Jikei University School of Medicine, Tokyo 105-8461, Japan
4
Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology, Gunma 370-1292, Japan
5
Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway
6
KG Jebsen Center for Cardiac Research, University of Oslo, Oslo, Norway
7
Department of Physics, Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan
*
Authors to whom correspondence should be addressed.
Nanomaterials 2020, 10(3), 532; https://doi.org/10.3390/nano10030532
Received: 18 February 2020 / Revised: 10 March 2020 / Accepted: 11 March 2020 / Published: 16 March 2020
(This article belongs to the Special Issue Application of Nanotechnology in Cardiology)
Myocardial contraction is initiated by action potential propagation through the conduction system of the heart. It has been thought that connexin 43 in the gap junctions (GJ) within the intercalated disc (ID) provides direct electric connectivity between cardiomyocytes (electronic conduction). However, recent studies challenge this view by providing evidence that the mechanosensitive cardiac sodium channels Nav1.5 localized in perinexii at the GJ edge play an important role in spreading action potentials between neighboring cells (ephaptic conduction). In the present study, we performed real-time confocal imaging of the CellMask-stained ID in the living mouse heart in vivo. We found that the ID structure was not rigid. Instead, we observed marked flexing of the ID during propagation of contraction from cell to cell. The variation in ID length was between ~30 and ~42 μm (i.e., magnitude of change, ~30%). In contrast, tracking of α-actinin-AcGFP revealed a comparatively small change in the lateral dimension of the transitional junction near the ID (i.e., magnitude of change, ~20%). The present findings suggest that, when the heart is at work, mechanostress across the perinexii may activate Nav1.5 by promoting ephaptic conduction in coordination with electronic conduction, and, thereby, efficiently transmitting excitation-contraction coupling between cardiomyocytes. View Full-Text
Keywords: myocardium; gap junction; action potential; heart myocardium; gap junction; action potential; heart
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Kobirumaki-Shimozawa, F.; Nakanishi, T.; Shimozawa, T.; Terui, T.; Oyama, K.; Li, J.; Louch, W.E.; Ishiwata, S.; Fukuda, N. Real-Time In Vivo Imaging of Mouse Left Ventricle Reveals Fluctuating Movements of the Intercalated Discs. Nanomaterials 2020, 10, 532.

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