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Lilliu E, Hackl B, Zabrodska E, Gewessler S, Karge T, Marksteiner J, Sauer J, Putz EM, Todt H, Hilber K, Koenig X. Cell size induced bias of current density in hypertrophic cardiomyocytes. Channels (Austin) 2024; 18:2361416. [PMID: 38836323 PMCID: PMC11155701 DOI: 10.1080/19336950.2024.2361416] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2024] [Accepted: 05/26/2024] [Indexed: 06/06/2024] Open
Abstract
Alterations in ion channel expression and function known as "electrical remodeling" contribute to the development of hypertrophy and to the emergence of arrhythmias and sudden cardiac death. However, comparing current density values - an electrophysiological parameter commonly utilized to assess ion channel function - between normal and hypertrophied cells may be flawed when current amplitude does not scale with cell size. Even more, common routines to study equally sized cells or to discard measurements when large currents do not allow proper voltage-clamp control may introduce a selection bias and thereby confound direct comparison. To test a possible dependence of current density on cell size and shape, we employed whole-cell patch-clamp recording of voltage-gated sodium and calcium currents in Langendorff-isolated ventricular cardiomyocytes and Purkinje myocytes, as well as in cardiomyocytes derived from trans-aortic constriction operated mice. Here, we describe a distinct inverse relationship between voltage-gated sodium and calcium current densities and cell capacitance both in normal and hypertrophied cells. This inverse relationship was well fit by an exponential function and may be due to physiological adaptations that do not scale proportionally with cell size or may be explained by a selection bias. Our study emphasizes the need to consider cell size bias when comparing current densities in cardiomyocytes of different sizes, particularly in hypertrophic cells. Conventional comparisons based solely on mean current density may be inadequate for groups with unequal cell size or non-proportional current amplitude and cell size scaling.
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Affiliation(s)
- Elena Lilliu
- Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Benjamin Hackl
- Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Eva Zabrodska
- Institute of Anatomy, First Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Stefanie Gewessler
- Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Tobias Karge
- Ludwig Boltzmann Institute for Cardiovascular Research at the Center for Biomedical Research and Translational Surgery, Medical University of Vienna, Vienna, Austria
| | - Jessica Marksteiner
- Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Jakob Sauer
- Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Eva M. Putz
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Hannes Todt
- Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Karlheinz Hilber
- Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Xaver Koenig
- Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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2
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Scardigli M, Pásek M, Santini L, Palandri C, Conti E, Crocini C, Campione M, Loew LM, de Vries AAF, Pijnappels DA, Pavone FS, Poggesi C, Cerbai E, Coppini R, Kohl P, Ferrantini C, Sacconi L. Optogenetic confirmation of transverse-tubular membrane excitability in intact cardiac myocytes. J Physiol 2024; 602:791-808. [PMID: 38348881 DOI: 10.1113/jp285202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Accepted: 01/17/2024] [Indexed: 03/09/2024] Open
Abstract
T-tubules (TT) form a complex network of sarcolemmal membrane invaginations, essential for well-co-ordinated excitation-contraction coupling (ECC) and thus homogeneous mechanical activation of cardiomyocytes. ECC is initiated by rapid depolarization of the sarcolemmal membrane. Whether TT membrane depolarization is active (local generation of action potentials; AP) or passive (following depolarization of the outer cell surface sarcolemma; SS) has not been experimentally validated in cardiomyocytes. Based on the assessment of ion flux pathways needed for AP generation, we hypothesize that TT are excitable. We therefore explored TT excitability experimentally, using an all-optical approach to stimulate and record trans-membrane potential changes in TT that were structurally disconnected, and hence electrically insulated, from the SS membrane by transient osmotic shock. Our results establish that cardiomyocyte TT can generate AP. These AP show electrical features that differ substantially from those observed in SS, consistent with differences in the density of ion channels and transporters in the two different membrane domains. We propose that TT-generated AP represent a safety mechanism for TT AP propagation and ECC, which may be particularly relevant in pathophysiological settings where morpho-functional changes reduce the electrical connectivity between SS and TT membranes. KEY POINTS: Cardiomyocytes are characterized by a complex network of membrane invaginations (the T-tubular system) that propagate action potentials to the core of the cell, causing uniform excitation-contraction coupling across the cell. In the present study, we investigated whether the T-tubular system is able to generate action potentials autonomously, rather than following depolarization of the outer cell surface sarcolemma. For this purpose, we developed a fully optical platform to probe and manipulate the electrical dynamics of subcellular membrane domains. Our findings demonstrate that T-tubules are intrinsically excitable, revealing distinct characteristics of self-generated T-tubular action potentials. This active electrical capability would protect cells from voltage drops potentially occurring within the T-tubular network.
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Affiliation(s)
- Marina Scardigli
- Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy
| | - Michal Pásek
- Institute of Thermomechanics, Czech Academy of Science, Prague, Czech Republic
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Lorenzo Santini
- Department of Neurology, Psychology, Drug Sciences and Child Health, University of Florence, Florence, Italy
| | - Chiara Palandri
- Department of Neurology, Psychology, Drug Sciences and Child Health, University of Florence, Florence, Italy
| | - Emilia Conti
- European Laboratory for Non-Linear Spectroscopy - LENS, Sesto Fiorentino, Italy
- Neuroscience Institute, National Research Council, Pisa, Italy
| | - Claudia Crocini
- DZHK (German Centre for Cardiovascular Research), Partner Site Berlin, Berlin, Germany
- Max Rubner Center for Cardiovascular Metabolic Renal Research (MRC), Deutsches Herzzentrum der Charité (DHZC), Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Marina Campione
- Institute of Neuroscience (IN-CNR) and Department of Biomedical Science, University of Padua, Padua, Italy
| | - Leslie M Loew
- Center for Cell Analysis and Modeling, University of Connecticut, Farmington, CT, USA
| | - Antoine A F de Vries
- Laboratory of Experimental Cardiology, Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Daniël A Pijnappels
- Laboratory of Experimental Cardiology, Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Francesco S Pavone
- European Laboratory for Non-Linear Spectroscopy - LENS, Sesto Fiorentino, Italy
| | - Corrado Poggesi
- Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy
| | - Elisabetta Cerbai
- Department of Neurology, Psychology, Drug Sciences and Child Health, University of Florence, Florence, Italy
- European Laboratory for Non-Linear Spectroscopy - LENS, Sesto Fiorentino, Italy
| | - Raffaele Coppini
- Department of Neurology, Psychology, Drug Sciences and Child Health, University of Florence, Florence, Italy
| | - Peter Kohl
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Medical Faculty, University of Freiburg, Freiburg, Germany
| | - Cecilia Ferrantini
- Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy
| | - Leonardo Sacconi
- European Laboratory for Non-Linear Spectroscopy - LENS, Sesto Fiorentino, Italy
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Medical Faculty, University of Freiburg, Freiburg, Germany
- Institute of Clinical Physiology, National Research Council (IFC-CNR), Florence, Italy
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3
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Vermij SH, Rougier JS, Agulló-Pascual E, Rothenberg E, Delmar M, Abriel H. Single-Molecule Localization of the Cardiac Voltage-Gated Sodium Channel Reveals Different Modes of Reorganization at Cardiomyocyte Membrane Domains. Circ Arrhythm Electrophysiol 2020; 13:e008241. [PMID: 32536203 PMCID: PMC7368852 DOI: 10.1161/circep.119.008241] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BACKGROUND Mutations in the gene encoding the cardiac voltage-gated sodium channel Nav1.5 cause various cardiac arrhythmias. This variety may arise from different determinants of Nav1.5 expression between cardiomyocyte domains. At the lateral membrane and T-tubules, Nav1.5 localization and function remain insufficiently characterized. METHODS We used novel single-molecule localization microscopy and computational modeling to define nanoscale features of Nav1.5 localization and distribution at the lateral membrane, the lateral membrane groove, and T-tubules in cardiomyocytes from wild-type (N=3), dystrophin-deficient (mdx; N=3) mice, and mice expressing C-terminally truncated Nav1.5 (ΔSIV; N=3). We moreover assessed T-tubules sodium current by recording whole-cell sodium currents in control (N=5) and detubulated (N=5) wild-type cardiomyocytes. RESULTS We show that Nav1.5 organizes as distinct clusters in the groove and T-tubules which density, distribution, and organization partially depend on SIV and dystrophin. We found that overall reduction in Nav1.5 expression in mdx and ΔSIV cells results in a nonuniform redistribution with Nav1.5 being specifically reduced at the groove of ΔSIV and increased in T-tubules of mdx cardiomyocytes. A T-tubules sodium current could, however, not be demonstrated. CONCLUSIONS Nav1.5 mutations may site-specifically affect Nav1.5 localization and distribution at the lateral membrane and T-tubules, depending on site-specific interacting proteins. Future research efforts should elucidate the functional consequences of this redistribution.
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Affiliation(s)
- Sarah H Vermij
- Institute of Biochemistry and Molecular Medicine, University of Bern, Switzerland (S.H.V., J.-S.R., H.A.)
| | - Jean-Sébastien Rougier
- Institute of Biochemistry and Molecular Medicine, University of Bern, Switzerland (S.H.V., J.-S.R., H.A.)
| | | | - Eli Rothenberg
- Department of Biochemistry and Pharmacology (E.R.), New York University School of Medicine, NY
| | - Mario Delmar
- Department of Cardiology (M.D.), New York University School of Medicine, NY
| | - Hugues Abriel
- Institute of Biochemistry and Molecular Medicine, University of Bern, Switzerland (S.H.V., J.-S.R., H.A.)
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Vermij SH, Abriel H, Kucera JP. Modeling Depolarization Delay, Sodium Currents, and Electrical Potentials in Cardiac Transverse Tubules. Front Physiol 2020; 10:1487. [PMID: 31920695 PMCID: PMC6916517 DOI: 10.3389/fphys.2019.01487] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 11/21/2019] [Indexed: 01/22/2023] Open
Abstract
T-tubules are invaginations of the lateral membrane of striated muscle cells that provide a large surface for ion channels and signaling proteins, thereby supporting excitation–contraction coupling. T-tubules are often remodeled in heart failure. To better understand the electrical behavior of T-tubules of cardiac cells in health and disease, this study addresses two largely unanswered questions regarding their electrical properties: (1) the delay of T-tubular membrane depolarization and (2) the effects of T-tubular sodium current on T-tubular potentials. Here, we present an elementary computational model to determine the delay in depolarization of deep T-tubular membrane segments as the narrow T-tubular lumen provides resistance against the extracellular current. We compare healthy tubules to tubules with constrictions and diseased tubules from mouse and human, and conclude that constrictions greatly delay T-tubular depolarization, while diseased T-tubules depolarize faster than healthy ones due to tubule widening. Increasing the tubule length non-linearly delays the depolarization. We moreover model the effect of T-tubular sodium current on intraluminal T-tubular potentials. We observe that extracellular potentials become negative during the sodium current transient (up to −40 mV in constricted T-tubules), which feedbacks on sodium channel function (self-attenuation) in a manner resembling ephaptic effects that have been described for intercalated discs where opposing membranes are very close together. The intraluminal potential and sodium current self-attenuation however greatly depend on sodium current conductance. These results show that (1) the changes in passive electrical properties of remodeled T-tubules cannot explain the excitation–contraction coupling defects in diseased cells; and (2) the sodium current may modulate intraluminal potentials. Such extracellular potentials might also affect excitation–contraction coupling and macroscopic conduction.
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Affiliation(s)
- Sarah Helena Vermij
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - Hugues Abriel
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
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