title: Electrotonic coupling of excitable and nonexcitable cells in the heart revealed by optogenetics.
abstract: Electrophysiological studies of excitable organs usually focus on action potential (AP)-generating cells, whereas nonexcitable cells are generally considered as barriers to electrical conduction. Whether nonexcitable cells may modulate excitable cell function or even contribute to AP conduction via direct electrotonic coupling to AP-generating cells is unresolved in the heart: such coupling is present in vitro, but conclusive evidence in situ is lacking. We used genetically encoded voltage-sensitive fluorescent protein 2.3 (VSFP2.3) to monitor transmembrane potential in either myocytes or nonmyocytes of murine hearts. We confirm that VSFP2.3 allows measurement of cell type-specific electrical activity. We show that VSFP2.3, expressed solely in nonmyocytes, can report cardiomyocyte AP-like signals at the border of healed cryoinjuries. Using EM-based tomographic reconstruction, we further discovered tunneling nanotube connections between myocytes and nonmyocytes in cardiac scar border tissue. Our results provide direct electrophysiological evidence of heterocellular electrotonic coupling in native myocardium and identify tunneling nanotubes as a possible substrate for electrical cell coupling that may be in addition to previously discovered connexins at sites of myocyte-nonmyocyte contact in the heart. These findings call for reevaluation of cardiac nonmyocyte roles in electrical connectivity of the heterocellular heart.
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2, Canada; alex.quinn@dal.ca peter.kohl@universitaets-herzzentrum.de.
authors.forename: T Alexander
authors.initials: TA
authors.lastname: Quinn
authors.affiliation: School of Biosciences and Medicine, University of Surrey, Guildford GU2 7XH, United Kingdom.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Camelliti
authors.affiliation: National Heart and Lung Institute, Imperial College London, Harefield UB9 6JH, United Kingdom.
authors.forename: Eva A
authors.initials: EA
authors.lastname: Rog-Zielinska
authors.affiliation: National Heart and Lung Institute, Imperial College London, Harefield UB9 6JH, United Kingdom.
authors.forename: Urszula
authors.initials: U
authors.lastname: Siedlecka
authors.affiliation: National Heart and Lung Institute, Imperial College London, Harefield UB9 6JH, United Kingdom.
authors.forename: Tommaso
authors.initials: T
authors.lastname: Poggioli
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309.
authors.forename: Eileen T
authors.initials: ET
authors.lastname: O'Toole
authors.affiliation: Department of Medicine, Imperial College London, London W12 0NN, United Kingdom.
authors.forename: Thomas
authors.initials: T
authors.lastname: Knöpfel
authors.affiliation: National Heart and Lung Institute, Imperial College London, Harefield UB9 6JH, United Kingdom; alex.quinn@dal.ca peter.kohl@universitaets-herzzentrum.de.|Institute for Experimental Cardiovascular Medicine, University Heart Centre Freiburg/Bad Krozingen, Medical School of the University of Freiburg, 79110 Freiburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Kohl
mesh_terms: D000200:Action Potentials; D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism; D002450:Cell Communication; D002452:Cell Count; D002462:Cell Membrane / Q000378:metabolism; D017630:Connexins / Q000378:metabolism*; D004553:Electric Conductivity; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D017629:Gap Junctions / Q000378:metabolism*; D006321:Heart / Q000502:physiology; D006329:Heart Conduction System / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008822:Mice, Transgenic; D032342:Muscle Cells / Q000378:metabolism; D009206:Myocardium / Q000166:cytology*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D062308:Optogenetics
chemical_list: D001426:Bacterial Proteins; D017630:Connexins; D008164:Luminescent Proteins; C054562:yellow fluorescent protein, Bacteria
keywords: cardiac; electrophysiology; fibroblast; genetically-encoded voltage indicator; heterocellular coupling