Quantitative assessment of passive electrical properties of the cardiac T-tubular system by FRAP microscopy

Year: 2017

Authors: Scardigli M., Crocini C., Ferrantini C., Gabbrielli T., Silvestri L., Coppini R., Tesi C., Rog-Zielinska E., Kohl P., Cerbai E., Poggesi C., Pavone F. S., Sacconi L.

Autors Affiliation: European Laboratory for Non-Linear Spectroscopy, 50019 Sesto Fiorentino, Italy; National Institute of Optics, National Research Council, 50019 Sesto Fiorentino, Italy; Division of Physiology, Department of Experimental and Clinical Medicine, University of Florence, 50121 Florence, Italy; Division of Pharmacology, Dipartimento di Neuroscienze, Psicologia, Area del Farmaco e Salute del Bambino, University of Florence, 50139 Florence, Italy; Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, Faculty of Medicine, University of Freiburg, 79110 Freiburg, Germany; The Magdi Yacoub Institute, National Heart and Lung Institute, Imperial College London, UB9 6JH London, United Kingdom; Department of Physics and Astronomy, University of Florence, 50019 Florence, Italy

Abstract: Well-coordinated activation of all cardiomyocytes must occur on every heartbeat. At the cell level, a complex network of sarcolemmal invaginations, called the transverse-axial tubular system (TATS), propagates membrane potential changes to the cell core, ensuring synchronous and uniformexcitation-contraction coupling. Although myocardial conduction of excitation has been widely described, the electrical properties of the TATS remain mostly unknown. Here, we exploit the formal analogy between diffusion and electrical conductivity to link the latter with the diffusional properties of TATS. Fluorescence recovery after photobleaching (FRAP) microscopy is used to probe the diffusion properties of TATS in isolated rat cardiomyocytes: A fluorescent dextran inside TATS lumen is photobleached, and signal recovery by diffusion of unbleached dextran from the extracellular space is monitored. We designed a mathematical model to correlate the time constant of fluorescence recovery with the apparent diffusion coefficient of the fluorescent molecules. Then, apparent diffusion is linked to electrical conductivity and used to evaluate the efficiency of the passive spread of membrane depolarization along TATS. The method is first validated in cells where most TATS elements are acutely detached by osmotic shock and then applied to probe TATS electrical conductivity in failing heart cells. We find that acute and pathological tubular remodeling significantly affect TATS electrical conductivity. This may explain the occurrence of defects in action potential propagation at the level of single T-tubules, recently observed in diseased cardiomyocytes.


Volume: 114 (22)      Pages from: 5737  to: 5742

More Information: We thank Dr. Marie Caroline Mullenbroich for helpful discussions on the manuscript. This work was supported by European Union
KeyWords: cardiac disease; transverse-axial tubular system; diffusion; electrical conductivity; porous rock
DOI: 10.1073/pnas.1702188114

Citations: 31
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