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Lang D, Medvedev RY, Ratajczyk L, Zheng J, Yuan X, Lim E, Han OY, Valdivia HH, Glukhov AV. Region-specific distribution of transversal-axial tubule system organization underlies heterogeneity of calcium dynamics in the right atrium. Am J Physiol Heart Circ Physiol 2022; 322:H269-H284. [PMID: 34951544 PMCID: PMC8782648 DOI: 10.1152/ajpheart.00381.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The atrial myocardium demonstrates the highly heterogeneous organization of the transversal-axial tubule system (TATS), although its anatomical distribution and region-specific impact on Ca2+ dynamics remain unknown. Here, we developed a novel method for high-resolution confocal imaging of TATS in intact live mouse atrial myocardium and applied a custom-developed MATLAB-based computational algorithm for the automated analysis of TATS integrity. We observed a twofold higher (P < 0.01) TATS density in the right atrial appendage (RAA) than in the intercaval regions (ICR, the anatomical region between the superior vena cava and atrioventricular junction and between the crista terminalis and interatrial septum). Whereas RAA predominantly consisted of well-tubulated myocytes, ICR showed partially tubulated/untubulated cells. Similar TATS distribution was also observed in healthy human atrial myocardium sections. In both mouse atrial preparations and isolated mouse atrial myocytes, we observed a strong anatomical correlation between TATS distribution and Ca2+ transient synchronization and rise-up time. This region-specific difference in Ca2+ transient morphology disappeared after formamide-induced detubulation. ICR myocytes showed a prolonged action potential duration at 80% of repolarization as well as a significantly lower expression of RyR2 and Cav1.2 proteins but similar levels of NCX1 and Cav1.3 compared with RAA tissue. Our findings provide a detailed characterization of the region-specific distribution of TATS in mouse and human atrial myocardium, highlighting the structural foundation for anatomical heterogeneity of Ca2+ dynamics and contractility in the atria. These results could indicate different roles of TATS in Ca2+ signaling at distinct anatomical regions of the atria and provide mechanistic insight into pathological atrial remodeling.NEW & NOTEWORTHY Mouse and human atrial myocardium demonstrate high variability in the organization of the transversal-axial tubule system (TATS), with more organized TATS expressed in the right atrial appendage. TATS distribution governs anatomical heterogeneity of Ca2+ dynamics and thus could contribute to integral atrial contractility, mechanics, and arrhythmogenicity.
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Affiliation(s)
- Di Lang
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
| | - Roman Y Medvedev
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
| | - Lucas Ratajczyk
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
| | - Jingjing Zheng
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
| | - Xiaoyu Yuan
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
| | - Evi Lim
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
| | - Owen Y Han
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
| | - Hector H Valdivia
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
| | - Alexey V Glukhov
- Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin
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2
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Setterberg IE, Le C, Frisk M, Li J, Louch WE. The Physiology and Pathophysiology of T-Tubules in the Heart. Front Physiol 2021; 12:718404. [PMID: 34566684 PMCID: PMC8458775 DOI: 10.3389/fphys.2021.718404] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Accepted: 07/07/2021] [Indexed: 12/18/2022] Open
Abstract
In cardiomyocytes, invaginations of the sarcolemmal membrane called t-tubules are critically important for triggering contraction by excitation-contraction (EC) coupling. These structures form functional junctions with the sarcoplasmic reticulum (SR), and thereby enable close contact between L-type Ca2+ channels (LTCCs) and Ryanodine Receptors (RyRs). This arrangement in turn ensures efficient triggering of Ca2+ release, and contraction. While new data indicate that t-tubules are capable of exhibiting compensatory remodeling, they are also widely reported to be structurally and functionally compromised during disease, resulting in disrupted Ca2+ homeostasis, impaired systolic and/or diastolic function, and arrhythmogenesis. This review summarizes these findings, while highlighting an emerging appreciation of the distinct roles of t-tubules in the pathophysiology of heart failure with reduced and preserved ejection fraction (HFrEF and HFpEF). In this context, we review current understanding of the processes underlying t-tubule growth, maintenance, and degradation, underscoring the involvement of a variety of regulatory proteins, including junctophilin-2 (JPH2), amphiphysin-2 (BIN1), caveolin-3 (Cav3), and newer candidate proteins. Upstream regulation of t-tubule structure/function by cardiac workload and specifically ventricular wall stress is also discussed, alongside perspectives for novel strategies which may therapeutically target these mechanisms.
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Affiliation(s)
- Ingunn E Setterberg
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - Christopher Le
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - Michael Frisk
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - Jia Li
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - William E Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
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3
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Wright PT, Gorelik J, Harding SE. Electrophysiological Remodeling: Cardiac T-Tubules and ß-Adrenoceptors. Cells 2021; 10:cells10092456. [PMID: 34572106 PMCID: PMC8468945 DOI: 10.3390/cells10092456] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 09/13/2021] [Accepted: 09/16/2021] [Indexed: 01/09/2023] Open
Abstract
Beta-adrenoceptors (βAR) are often viewed as archetypal G-protein coupled receptors. Over the past fifteen years, investigations in cardiovascular biology have provided remarkable insights into this receptor family. These studies have shifted pharmacological dogma, from one which centralized the receptor to a new focus on structural micro-domains such as caveolae and t-tubules. Important studies have examined, separately, the structural compartmentation of ion channels and βAR. Despite links being assumed, relatively few studies have specifically examined the direct link between structural remodeling and electrical remodeling with a focus on βAR. In this review, we will examine the nature of receptor and ion channel dysfunction on a substrate of cardiomyocyte microdomain remodeling, as well as the likely ramifications for cardiac electrophysiology. We will then discuss the advances in methodologies in this area with a specific focus on super-resolution microscopy, fluorescent imaging, and new approaches involving microdomain specific, polymer-based agonists. The advent of powerful computational modelling approaches has allowed the science to shift from purely empirical work, and may allow future investigations based on prediction. Issues such as the cross-reactivity of receptors and cellular heterogeneity will also be discussed. Finally, we will speculate as to the potential developments within this field over the next ten years.
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Affiliation(s)
- Peter T. Wright
- School of Life & Health Sciences, University of Roehampton, Holybourne Avenue, London SW15 4JD, UK;
- Cardiac Section, National Heart and Lung Institute (NHLI), Faculty of Medicine, Imperial College London, Hammersmith Campus, Du Cane Road, London W12 0NN, UK;
| | - Julia Gorelik
- Cardiac Section, National Heart and Lung Institute (NHLI), Faculty of Medicine, Imperial College London, Hammersmith Campus, Du Cane Road, London W12 0NN, UK;
| | - Sian E. Harding
- Cardiac Section, National Heart and Lung Institute (NHLI), Faculty of Medicine, Imperial College London, Hammersmith Campus, Du Cane Road, London W12 0NN, UK;
- Correspondence:
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4
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Mahapatra A, Uysalel C, Rangamani P. The Mechanics and Thermodynamics of Tubule Formation in Biological Membranes. J Membr Biol 2021; 254:273-291. [PMID: 33462667 PMCID: PMC8184589 DOI: 10.1007/s00232-020-00164-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Accepted: 12/11/2020] [Indexed: 02/07/2023]
Abstract
Membrane tubulation is a ubiquitous process that occurs both at the plasma membrane and on the membranes of intracellular organelles. These tubulation events are known to be mediated by forces applied on the membrane either due to motor proteins, by polymerization of the cytoskeleton, or due to the interactions between membrane proteins binding onto the membrane. The numerous experimental observations of tube formation have been amply supported by mathematical modeling of the associated membrane mechanics and have provided insights into the force-displacement relationships of membrane tubes. Recent advances in quantitative biophysical measurements of membrane-protein interactions and tubule formation have necessitated the need for advances in modeling that will account for the interplay of multiple aspects of physics that occur simultaneously. Here, we present a comprehensive review of experimental observations of tubule formation and provide context from the framework of continuum modeling. Finally, we explore the scope for future research in this area with an emphasis on iterative modeling and experimental measurements that will enable us to expand our mechanistic understanding of tubulation processes in cells.
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Affiliation(s)
- Arijit Mahapatra
- Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Dr, La Jolla, CA, 92093, USA
| | - Can Uysalel
- Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Dr, La Jolla, CA, 92093, USA
| | - Padmini Rangamani
- Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Dr, La Jolla, CA, 92093, USA.
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5
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Lu F, Pu WT. The architecture and function of cardiac dyads. Biophys Rev 2020; 12:1007-1017. [PMID: 32661902 PMCID: PMC7429583 DOI: 10.1007/s12551-020-00729-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Accepted: 07/03/2020] [Indexed: 12/28/2022] Open
Abstract
Cardiac excitation-contraction (EC) coupling, which links plasma membrane depolarization to activation of cardiomyocyte contraction, occurs at dyads, the nanoscopic microdomains formed by apposition of transverse (T)-tubules and junctional sarcoplasmic reticulum (jSR). In a dyadic junction, EC coupling occurs through Ca2+-induced Ca2+ release. Membrane depolarization opens voltage-gated L-type Ca2+ channels (LTCCs) in the T-tubule. The resulting influx of extracellular Ca2+ into the dyadic cleft opens Ca2+ release channels known as ryanodine receptors (RYRs) in the jSR, leading to the rapid increase in cytosolic Ca2+ that triggers sarcomere contraction. The efficacy of LTCC-RYR communication greatly affects a myriad of downstream intracellular signaling events, and it is controlled by many factors, including T-tubule and jSR structure, spatial distribution of ion channels, and regulatory proteins that closely regulate the activities of channels within dyads. Alterations in dyad architecture and/or channel activity are seen in many types of heart disease. This review will focus on the current knowledge regarding cardiac dyad structure and function, their alterations in heart failure, and new approaches to study the composition and function of dyads.
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Affiliation(s)
- Fujian Lu
- Department of Cardiology, Boston Children's Hospital, 300 Longwood Ave, Boston, MA, 02115, USA
| | - William T Pu
- Department of Cardiology, Boston Children's Hospital, 300 Longwood Ave, Boston, MA, 02115, USA.
- Harvard Stem Cell Institute, 7 Divinity Avenue, Cambridge, MA, 02138, USA.
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6
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Spinozzi S, Liu C, Chen Z, Feng W, Zhang L, Ouyang K, Evans SM, Chen J. Nexilin Is Necessary for Maintaining the Transverse-Axial Tubular System in Adult Cardiomyocytes. Circ Heart Fail 2020; 13:e006935. [PMID: 32635769 PMCID: PMC7583668 DOI: 10.1161/circheartfailure.120.006935] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Accepted: 03/31/2020] [Indexed: 01/28/2023]
Abstract
BACKGROUND NEXN (nexilin) is a protein of the junctional membrane complex required for development of cardiac T-tubules. Global and cardiomyocyte-specific loss of Nexn in mice leads to a rapidly progressive dilated cardiomyopathy and premature death. Therefore, little is known as to the role of NEXN in adult cardiomyocytes. Transverse-axial tubular system remodeling are well-known features in heart failure. Although NEXN is required during development for T-tubule formation, its role, if any, in mature T-tubules remains to be addressed. METHODS Nexn inducible adult cardiomyocyte-specific KO mice were generated. Comprehensive morphological and functional analyses were performed. Heart samples (n>3) were analyzed by molecular, biochemical, and electron microscopy analyses. Isolated single adult cardiomyocytes were analyzed by confocal microscopy, and myocyte shortening/re-lengthening and Ca2+ transient studies were conducted. RESULTS Inducible cardiomyocyte-specific loss of Nexn in adult mice resulted in a dilated cardiomyopathy with reduced cardiac function (13% reduction in percentage fractional shortening; P<0.05). In vivo and in vitro analyses of adult mouse heart samples revealed that NEXN was essential for optimal contraction and calcium handling and was required for maintenance of T-tubule network organization (transverse tubular component in Nexn inducible adult cardiomyocyte-specific KO mice reduced by 40% with respect to controls, P<0.05). CONCLUSIONS Results here reported reveal NEXN to be a pivotal component of adult junctional membrane complexes required for maintenance of transverse-axial tubular architecture. These results demonstrate that NEXN plays an essential role in the adult cardiomyocyte and give further understanding of pathological mechanisms responsible for cardiomyopathy in patients carrying mutations in the NEXN gene.
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MESH Headings
- Age Factors
- Animals
- Calcium/metabolism
- Cardiomyopathy, Dilated/genetics
- Cardiomyopathy, Dilated/metabolism
- Cardiomyopathy, Dilated/physiopathology
- Disease Models, Animal
- Mice
- Mice, Knockout
- Microfilament Proteins/genetics
- Microfilament Proteins/metabolism
- Microfilament Proteins/physiology
- Microtubules/metabolism
- Microtubules/physiology
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/physiology
- Ventricular Dysfunction, Left/genetics
- Ventricular Dysfunction, Left/metabolism
- Ventricular Dysfunction, Left/physiopathology
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Affiliation(s)
- Simone Spinozzi
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Canzhao Liu
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Ze’e Chen
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Wei Feng
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Lunfeng Zhang
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
- Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Kunfu Ouyang
- Drug Discovery Center, State Key Laboratory of Chemical Oncogenomics, School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, Shenzhen 518055, China
| | - Sylvia M. Evans
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
- Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, CA 92093, USA
| | - Ju Chen
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
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7
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Introducing a mammalian nerve-muscle preparation ideal for physiology and microscopy, the transverse auricular muscle in the ear of the mouse. Neuroscience 2019; 439:80-105. [PMID: 31351140 DOI: 10.1016/j.neuroscience.2019.07.028] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 07/10/2019] [Accepted: 07/15/2019] [Indexed: 11/23/2022]
Abstract
A new mammalian neuromuscular preparation is introduced for physiology and microscopy of all sorts: the intrinsic muscle of the mouse ear. The great utility of this preparation is demonstrated by illustrating how it has permitted us to develop a wholly new technique for staining muscle T-tubules, the critical conductive-elements in muscle. This involves sequential immersion in dilute solutions of osmium and ferrocyanide, then tannic acid, and then uranyl acetate, all of which totally blackens the T-tubules but leaves the muscle pale, thereby revealing that the T-tubules in mouse ear-muscles become severely distorted in several pathological conditions. These include certain mouse-models of muscular dystrophy (specifically, dysferlin-mutations), certain mutations of muscle cytoskeletal proteins (specifically, beta-tubulin mutations), and also in denervation-fibrillation, as observed in mouse ears maintained with in vitro tissue-culture conditions. These observations permit us to generate the hypothesis that T-tubules are the "Achilles' heel" in several adult-onset muscular dystrophies, due to their unique susceptibility to damage via muscle lattice-dislocations. These new observations strongly encourage further in-depth studies of ear-muscle architecture, in the many available mouse-models of various devastating human muscle-diseases. Finally, we demonstrate that the delicate and defined physical characteristics of this 'new' mammalian muscle are ideal for ultrastructural study, and thereby facilitate the imaging of synaptic vesicle membrane recycling in mammalian neuromuscular junctions, a topic that is critical to myasthenia gravis and related diseases, but which has, until now, completely eluded electron microscopic analysis. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.
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8
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An expanded proteome of cardiac t-tubules. Cardiovasc Pathol 2019; 42:15-20. [PMID: 31202980 DOI: 10.1016/j.carpath.2019.05.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 04/29/2019] [Accepted: 05/17/2019] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND Transverse tubules (t-tubules) are important structural elements, derived from sarcolemma, found on all striated myocytes. These specialized organelles create a scaffold for many proteins crucial to the effective propagation of signal in cardiac excitation-contraction coupling. The full protein composition of this region is unknown. METHODS We characterized the t-tubule subproteome using 52,033 immunohistochemical images covering 13,203 proteins from the Human Protein Atlas (HPA) cardiac tissue microarrays. We used HPASubC, a suite of Python tools, to rapidly review and classify each image for a specific t-tubule staining pattern. The tools Gene Cards, String 11, and Gene Ontology Consortium as well as literature searches were used to understand pathways and relationships between the proteins. RESULTS There were 96 likely t-tubule proteins identified by HPASubC. Of these, 12 were matrisome proteins and 3 were mitochondrial proteins. A separate literature search identified 50 known t-tubule proteins. A comparison of the 2 lists revealed only 17 proteins in common, including 8 of the matrisome proteins. String11 revealed that 94 of 127 combined t-tubule proteins generated a single interconnected network. CONCLUSION Using HPASubC and the HPA, we identified 78 novel, putative t-tubule proteins and validated 17 within the literature. This expands and improves our knowledge of this important subcellular structure of the cardiac myocyte. This information can be used to identify new structural targets involved in excitation-contraction coupling that may be altered in disease.
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9
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Brandenburg S, Pawlowitz J, Fakuade FE, Kownatzki-Danger D, Kohl T, Mitronova GY, Scardigli M, Neef J, Schmidt C, Wiedmann F, Pavone FS, Sacconi L, Kutschka I, Sossalla S, Moser T, Voigt N, Lehnart SE. Axial Tubule Junctions Activate Atrial Ca 2+ Release Across Species. Front Physiol 2018; 9:1227. [PMID: 30349482 PMCID: PMC6187065 DOI: 10.3389/fphys.2018.01227] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Accepted: 08/14/2018] [Indexed: 01/10/2023] Open
Abstract
Rationale: Recently, abundant axial tubule (AT) membrane structures were identified deep inside atrial myocytes (AMs). Upon excitation, ATs rapidly activate intracellular Ca2+ release and sarcomeric contraction through extensive AT junctions, a cell-specific atrial mechanism. While AT junctions with the sarcoplasmic reticulum contain unusually large clusters of ryanodine receptor 2 (RyR2) Ca2+ release channels in mouse AMs, it remains unclear if similar protein networks and membrane structures exist across species, particularly those relevant for atrial disease modeling. Objective: To examine and quantitatively analyze the architecture of AT membrane structures and associated Ca2+ signaling proteins across species from mouse to human. Methods and Results: We developed superresolution microscopy (nanoscopy) strategies for intact live AMs based on a new custom-made photostable cholesterol dye and immunofluorescence imaging of membraneous structures and membrane proteins in fixed tissue sections from human, porcine, and rodent atria. Consistently, in mouse, rat, and rabbit AMs, intact cell-wide tubule networks continuous with the surface membrane were observed, mainly composed of ATs. Moreover, co-immunofluorescence nanoscopy showed L-type Ca2+ channel clusters adjacent to extensive junctional RyR2 clusters at ATs. However, only junctional RyR2 clusters were highly phosphorylated and may thus prime Ca2+ release at ATs, locally for rapid signal amplification. While the density of the integrated L-type Ca2+ current was similar in human and mouse AMs, the intracellular Ca2+ transient showed quantitative differences. Importantly, local intracellular Ca2+ release from AT junctions occurred through instantaneous action potential propagation via transverse tubules (TTs) from the surface membrane. Hence, sparse TTs were sufficient as electrical conduits for rapid activation of Ca2+ release through ATs. Nanoscopy of atrial tissue sections confirmed abundant ATs as the major network component of AMs, particularly in human atrial tissue sections. Conclusion: AT junctions represent a conserved, cell-specific membrane structure for rapid excitation-contraction coupling throughout a representative spectrum of species including human. Since ATs provide the major excitable membrane network component in AMs, a new model of atrial “super-hub” Ca2+ signaling may apply across biomedically relevant species, opening avenues for future investigations about atrial disease mechanisms and therapeutic targeting.
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Affiliation(s)
- Sören Brandenburg
- Heart Research Center Göttingen, Department of Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany
| | - Jan Pawlowitz
- Heart Research Center Göttingen, Department of Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany
| | - Funsho E Fakuade
- Heart Research Center Göttingen, Institute of Pharmacology and Toxicology, University Medical Center Göttingen, Göttingen, Germany
| | - Daniel Kownatzki-Danger
- Heart Research Center Göttingen, Department of Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany
| | - Tobias Kohl
- Heart Research Center Göttingen, Department of Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany
| | - Gyuzel Y Mitronova
- Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Marina Scardigli
- European Laboratory for Non-Linear Spectroscopy and National Institute of Optics (INO-CNR), Sesto Fiorentino, Italy
| | - Jakob Neef
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
| | - Constanze Schmidt
- Heart Research Center Göttingen, Department of Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany.,DZHK (German Centre for Cardiovascular Research) partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany.,Heidelberg Center for Heart Rhythm Disorders, University Hospital Heidelberg, Heidelberg, Germany
| | - Felix Wiedmann
- Department of Cardiology, University Hospital Heidelberg, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research) partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany.,Heidelberg Center for Heart Rhythm Disorders, University Hospital Heidelberg, Heidelberg, Germany
| | - Francesco S Pavone
- European Laboratory for Non-Linear Spectroscopy and National Institute of Optics (INO-CNR), Sesto Fiorentino, Italy.,Department of Physics, University of Florence, Florence, Italy
| | - Leonardo Sacconi
- European Laboratory for Non-Linear Spectroscopy and National Institute of Optics (INO-CNR), Sesto Fiorentino, Italy
| | - Ingo Kutschka
- Department of Cardiothoracic and Vascular Surgery, University Medical Center Göttingen, Göttingen, Germany
| | - Samuel Sossalla
- Heart Research Center Göttingen, Department of Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany
| | - Niels Voigt
- Heart Research Center Göttingen, Institute of Pharmacology and Toxicology, University Medical Center Göttingen, Göttingen, Germany.,DZHK (German Centre for Cardiovascular Research) partner site Göttingen, Göttingen, Germany
| | - Stephan E Lehnart
- Heart Research Center Göttingen, Department of Cardiology and Pneumology, University Medical Center Göttingen, Göttingen, Germany.,DZHK (German Centre for Cardiovascular Research) partner site Göttingen, Göttingen, Germany.,BioMET, The Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD, United States
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10
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Abstract
Cardiac transverse (t-) tubules carry both electrical excitation and solutes toward the cell center but their ability to transport small molecules is unclear. While fluorescence recovery after photobleaching (FRAP) can provide an approach to measure local solute movement, extraction of diffusion coefficients is confounded by cell and illumination beam geometries. In this study, we use measured cellular geometry and detailed computer modeling to derive the apparent diffusion coefficient of a 1-kDa solute inside the t-tubular system of rabbit and mouse ventricular cardiomyocytes. This approach shows that diffusion within individual t-tubules is more rapid than previously reported. T-tubule tortuosity, varicosities, and the presence of longitudinal elements combine to substantially reduce the apparent rate of solute movement. In steady state, large (>4 kDa) solutes did not freely fill the t-tubule lumen of both species and <50% of the t-tubule volume was available to solutes >70 kDa. Detailed model fitting of FRAP data suggests that solute diffusion is additionally restricted at the t-tubular entrance and this effect was larger in mouse than in rabbit. The possible structural basis of this effect was investigated using electron microscopy and tomography. Near the cell surface, mouse t-tubules are more tortuous and filled with an electron-dense ground substance, previously identified as glycocalyx and a polyanionic mesh. Solute movement in the t-tubule network of rabbit and mouse appears to be explained by their different geometric properties, which impacts the use of these species for understanding t-tubule function and the consequences of changes associated with t-tubule disease.
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11
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Kim JC, Son MJ, Wang J, Woo SH. Regulation of cardiac Ca 2+ and ion channels by shear mechanotransduction. Arch Pharm Res 2017; 40:783-795. [PMID: 28702845 DOI: 10.1007/s12272-017-0929-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2017] [Accepted: 07/06/2017] [Indexed: 11/25/2022]
Abstract
Cardiac contraction is controlled by a Ca2+ signaling sequence that includes L-type Ca2+ current-gated opening of Ca2+ release channels (ryanodine receptors) in the sarcoplasmic reticulum (SR). Local Ca2+ signaling in the atrium differs from that in the ventricle because atrial myocytes lack transverse tubules and have more abundant corbular SR. Myocardium is subjected to a variety of forces with each contraction, such as stretch, shear stress, and afterload, and adapts to those mechanical stresses. These mechanical stimuli increase in heart failure, hypertension, and valvular heart diseases that are clinically implicated in atrial fibrillation and stroke. In the present review, we describe distinct responses of atrial and ventricular myocytes to shear stress and compare them with other mechanical responses in the context of local and global Ca2+ signaling and ion channel regulation. Recent evidence suggests that shear mechanotransduction in cardiac myocytes involves activation of gap junction hemichannels, purinergic signaling, and generation of mitochondrial reactive oxygen species. Significant alterations in Ca2+ signaling and ionic currents by shear stress may be implicated in the pathogenesis of cardiac arrhythmia and failure.
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Affiliation(s)
- Joon-Chul Kim
- College of Pharmacy, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon, 305-764, South Korea
| | - Min-Jeong Son
- College of Pharmacy, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon, 305-764, South Korea
| | - Jun Wang
- College of Pharmacy, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon, 305-764, South Korea
| | - Sun-Hee Woo
- College of Pharmacy, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon, 305-764, South Korea.
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12
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Kong CHT, Rog-Zielinska EA, Orchard CH, Kohl P, Cannell MB. Sub-microscopic analysis of t-tubule geometry in living cardiac ventricular myocytes using a shape-based analysis method. J Mol Cell Cardiol 2017; 108:1-7. [PMID: 28483597 PMCID: PMC5529290 DOI: 10.1016/j.yjmcc.2017.05.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 05/01/2017] [Accepted: 05/03/2017] [Indexed: 12/30/2022]
Abstract
Transverse-axial tubules (TTs) are key structures involved in cardiac excitation-contraction coupling and can become deranged in disease. Although optical measurement of TTs is frequently employed to assess TT abundance and regularity, TT dimensions are generally below the diffraction limit of optical microscopy so determination of tubule size is problematic. TT diameter was measured by labeling both local surface membrane area and volume with fluorescent probes (FM4-64 and calcein, respectively), correcting image asymmetry by image processing and using the relationship between surface area and volume for a geometric primitive. This method shows that TTs have a mean (± SEM) diameter of 356 ± 18 nm in rabbit and 169 ± 15 nm in mouse (p < 0.001). Rabbit TT diameters were more variable than those of mouse (p < 0.01) and the smallest TT detected was 41 nm in mouse and the largest 695 nm in rabbit. These estimates are consistent with TT diameters derived from the more limited sampling of high-pressure frozen samples by electron tomography (which examines only a small fraction of the cell volume). Other measures of TT abundance and geometry (such as volume, membrane fractions and direction) were also derived. On the physiological time scale of E-C coupling (milliseconds), the average TT electrical space constant is ~ 175 μm in rabbit and ~ 120 μm in mouse and is ~ 50% of the steady-state space constant. This is sufficient to ensure reasonable electrical uniformity across normal cells. The image processing strategy and shape-based 3D approach to feature quantification is also generally applicable to other problems in quantification of sub-cellular anatomy. Living cardiomyocytes were dual-labeled with fluorescent surface and volume probes. A novel 3D image processing strategy enabled calculation of t-tubule diameter. The method shows rabbit and mouse t-tubules have quite different morphologies. Mean diameters of rabbit and mouse t-tubules were 360 and 170 nm, respectively. Estimated electrical space constants are sufficient to ensure electrical uniformity.
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Affiliation(s)
- Cherrie H T Kong
- School of Physiology, Pharmacology & Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom
| | - Eva A Rog-Zielinska
- National Heart and Lung Institute, Harefield Heart Science Centre, Imperial College London, Harefield UB9 6JH, United Kingdom
| | - Clive H Orchard
- School of Physiology, Pharmacology & Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom
| | - Peter Kohl
- National Heart and Lung Institute, Harefield Heart Science Centre, Imperial College London, Harefield UB9 6JH, United Kingdom; Institute for Experimental Cardiovascular Medicine, University Heart Centre Freiburg - Bad Krozingen, Medical School of the University of Freiburg, Elsaesser Str 2Q, 79110 Freiburg, Germany
| | - Mark B Cannell
- School of Physiology, Pharmacology & Neuroscience, Faculty of Biomedical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom.
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13
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Veeraraghavan R, Györke S, Radwański PB. Neuronal sodium channels: emerging components of the nano-machinery of cardiac calcium cycling. J Physiol 2017; 595:3823-3834. [PMID: 28195313 DOI: 10.1113/jp273058] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 12/05/2016] [Indexed: 01/07/2023] Open
Abstract
Excitation-contraction coupling is the bridge between cardiac electrical activation and mechanical contraction. It is driven by the influx of Ca2+ across the sarcolemma triggering Ca2+ release from the sarcoplasmic reticulum (SR) - a process termed Ca2+ -induced Ca2+ release (CICR) - followed by re-sequestration of Ca2+ into the SR. The Na+ /Ca2+ exchanger inextricably couples the cycling of Ca2+ and Na+ in cardiac myocytes. Thus, influx of Na+ via voltage-gated Na+ channels (NaV ) has emerged as an important regulator of CICR both in health and in disease. Recent insights into the subcellular distribution of cardiac and neuronal NaV isoforms and their ultrastructural milieu have important implications for the roles of these channels in mediating Ca2+ -driven arrhythmias. This review will discuss functional insights into the role of neuronal NaV isoforms vis-à-vis cardiac NaV s in triggering such arrhythmias and their potential as therapeutic targets in the context of the aforementioned structural observations.
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Affiliation(s)
- Rengasayee Veeraraghavan
- Virginia Tech Carilion Research Institute, and Center for Heart and Regenerative Medicine, Virginia Polytechnic University, Roanoke, VA, USA
| | - Sándor Györke
- Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, Ohio State University Wexner Medical Center, 473 West 12th Avenue, Room 510, Columbus, OH, 43210, USA.,Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, OH, USA
| | - Przemysław B Radwański
- Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, Ohio State University Wexner Medical Center, 473 West 12th Avenue, Room 510, Columbus, OH, 43210, USA.,Department of Physiology and Cell Biology, College of Medicine, Ohio State University, Columbus, OH, USA.,Division of Pharmacy Practice and Science, College of Pharmacy, Ohio State University, Columbus, OH, USA
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14
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Abstract
Unique to striated muscle cells, transverse tubules (t-tubules) are membrane organelles that consist of sarcolemma penetrating into the myocyte interior, forming a highly branched and interconnected network. Mature t-tubule networks are found in mammalian ventricular cardiomyocytes, with the transverse components of t-tubules occurring near sarcomeric z-discs. Cardiac t-tubules contain membrane microdomains enriched with ion channels and signaling molecules. The microdomains serve as key signaling hubs in regulation of cardiomyocyte function. Dyad microdomains formed at the junctional contact between t-tubule membrane and neighboring sarcoplasmic reticulum are critical in calcium signaling and excitation-contraction coupling necessary for beat-to-beat heart contraction. In this review, we provide an overview of the current knowledge in gross morphology and structure, membrane and protein composition, and function of the cardiac t-tubule network. We also review in detail current knowledge on the formation of functional membrane subdomains within t-tubules, with a particular focus on the cardiac dyad microdomain. Lastly, we discuss the dynamic nature of t-tubules including membrane turnover, trafficking of transmembrane proteins, and the life cycles of membrane subdomains such as the cardiac BIN1-microdomain, as well as t-tubule remodeling and alteration in diseased hearts. Understanding cardiac t-tubule biology in normal and failing hearts is providing novel diagnostic and therapeutic opportunities to better treat patients with failing hearts.
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Affiliation(s)
- TingTing Hong
- Cedars-Sinai Heart Institute, Cedars-Sinai Medical Center, Los Angeles, California; and Department of Medicine, University of California Los Angeles, Los Angeles, California
| | - Robin M Shaw
- Cedars-Sinai Heart Institute, Cedars-Sinai Medical Center, Los Angeles, California; and Department of Medicine, University of California Los Angeles, Los Angeles, California
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15
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Crocini C, Ferrantini C, Coppini R, Sacconi L. Electrical defects of the transverse-axial tubular system in cardiac diseases. J Physiol 2017; 595:3815-3822. [PMID: 27981580 PMCID: PMC5471422 DOI: 10.1113/jp273042] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 11/21/2016] [Indexed: 01/20/2023] Open
Abstract
Electrical excitability is an essential feature of cardiomyocytes and the homogenous propagation of the action potential is guaranteed by a complex network of membrane invaginations called the transverse-axial tubular system (TATS). TATS structural remodelling is a hallmark of cardiac diseases and we demonstrated that this can be accompanied by electrical defects at single T-tubular level. Using a random-access multi-photon (RAMP) microscope, we found that pathological T-tubules can fail to conduct action potentials, which delays local Ca2+ release. Although the underlying causes for T-tubular electrical failure are still unknown, our findings suggest that they are likely to be related to local ultrastructural alterations. Here, we first review the experimental approach that allowed us to observe and dissect the consequences of TATS electrical dysfunction and then propose two different strategies to unveil the reasons for T-tubular electrical failures. The first strategy consists in a correlative approach, in which the failing T-tubule identified with the RAMP microscope is then imaged with electron microscopy. The second approach exploits the diffusion of molecules within TATS to gain insights into the local TATS structure, even without a thorough reconstruction of the tubular network. Although challenging, the local electrical failure occurring at single T-tubules is a fundamental question that needs to be addressed and could provide novel insights in cardiac pathophysiology.
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Affiliation(s)
- Claudia Crocini
- European Laboratory for Non-Linear Spectroscopy, 50019, Sesto Fiorentino, Italy.,National Institute of Optics, National Research Council, 50125, Florence, Italy
| | - Cecilia Ferrantini
- Division of Physiology, Department of Experimental and Clinical Medicine, University of Florence, 50134, Florence, Italy
| | - Raffaele Coppini
- Division of Pharmacology, Department 'NeuroFarBa', University of Florence, 50139, Florence, Italy
| | - Leonardo Sacconi
- European Laboratory for Non-Linear Spectroscopy, 50019, Sesto Fiorentino, Italy.,National Institute of Optics, National Research Council, 50125, Florence, Italy
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16
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Bennett PM, Ehler E, Wilson AJ. Sarcoplasmic reticulum is an intermediary of mitochondrial and myofibrillar growth at the intercalated disc. J Muscle Res Cell Motil 2016; 37:55-69. [PMID: 27329158 PMCID: PMC5010836 DOI: 10.1007/s10974-016-9444-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 05/22/2016] [Indexed: 11/30/2022]
Abstract
In cardiomyocytes columns of intermyofibrillar mitochondria run up to the intercalated disc (ID); half are collinear with those in the neighbouring cell, suggesting coordinated addition of sarcomeres and mitochondria both within and between cells during cardiomyocyte growth. Recent evidence for an association between sarcoplasmic reticulum (SR) and mitochondria indicates that the SR may be an intermediary in this coordinated behaviour. For this reason we have investigated the arrangement of SR and t tubules with respect to mitochondria and myofibrils, particularly at the ID. In the body of the cardiomyocyte the mitochondrial columns are frequently intersected by transverse tubules. In addition, we find that a majority of axial tubules are sandwiched between mitochondria and myofibril. No tubules are found at the ID. SR coats mitochondrial columns and fibrils throughout their length and reaches towards the peaks of the ID membrane where it attaches in the form of junctional (j)SR. These peripheral ID couplings are often situated between mitochondria and ID membrane, suggesting an SR connection between the two. In dilated cardiomyopathy (DCM) the mitochondria are somewhat disordered and clumped. In a mouse model for DCM, the muscle LIM protein KO, we find that there is a lack of mitochondria near the ID, suggesting the uncoupling of the myofibril/mitochondria organisation during growth. SR still coats the fibrils and reaches the ID folds in a jSR coupling. Unlike in control tissue, however, loops and long fingers of ID membrane penetrate into the proximal sarcomere suggesting a possible intermediary state in cardiomyocyte growth.
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Affiliation(s)
- Pauline M Bennett
- Randall Division of Cell and Molecular Biophysics, King's College London, New Hunt's House, Guy's Campus, London, SE1 1UL, UK.
| | - Elisabeth Ehler
- Randall Division of Cell and Molecular Biophysics, King's College London, New Hunt's House, Guy's Campus, London, SE1 1UL, UK
| | - Amanda J Wilson
- Randall Division of Cell and Molecular Biophysics, King's College London, New Hunt's House, Guy's Campus, London, SE1 1UL, UK.,Department of Life Sciences, Sir Ernst Chain Building, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK
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17
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Gadeberg HC, Bond RC, Kong CHT, Chanoit GP, Ascione R, Cannell MB, James AF. Heterogeneity of T-Tubules in Pig Hearts. PLoS One 2016; 11:e0156862. [PMID: 27281038 PMCID: PMC4900646 DOI: 10.1371/journal.pone.0156862] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2014] [Accepted: 04/30/2016] [Indexed: 12/15/2022] Open
Abstract
Background T-tubules are invaginations of the sarcolemma that play a key role in excitation-contraction coupling in mammalian cardiac myocytes. Although t-tubules were generally considered to be effectively absent in atrial myocytes, recent studies on atrial cells from larger mammals suggest that t-tubules may be more numerous than previously supposed. However, the degree of heterogeneity between cardiomyocytes in the extent of the t-tubule network remains unclear. The aim of the present study was to investigate the t-tubule network of pig atrial myocytes in comparison with ventricular tissue. Methods Cardiac tissue was obtained from young female Landrace White pigs (45–75 kg, 5–6 months old). Cardiomyocytes were isolated by arterial perfusion with a collagenase-containing solution. Ca2+ transients were examined in field-stimulated isolated cells loaded with fluo-4-AM. Membranes of isolated cells were visualized using di-8-ANEPPS. T-tubules were visualized in fixed-frozen tissue sections stained with Alexa-Fluor 488-conjugated WGA. Binary images were obtained by application of a threshold and t-tubule density (TTD) calculated. A distance mapping approach was used to calculate half-distance to nearest t-tubule (HDTT). Results & Conclusion The spatio-temporal properties of the Ca2+ transient appeared to be consistent with the absence of functional t-tubules in isolated atrial myocytes. However, t-tubules could be identified in a sub-population of atrial cells in frozen sections. While all ventricular myocytes had TTD >3% (mean TTD = 6.94±0.395%, n = 24), this was true of just 5/22 atrial cells. Mean atrial TTD (2.35±0.457%, n = 22) was lower than ventricular TTD (P<0.0001). TTD correlated with cell-width (r = 0.7756, n = 46, P<0.0001). HDTT was significantly greater in the atrial cells with TTD ≤3% (2.29±0.16 μm, n = 17) than in either ventricular cells (1.33±0.05 μm, n = 24, P<0.0001) or in atrial cells with TTD >3% (1.65±0.06 μm, n = 5, P<0.05). These data demonstrate considerable heterogeneity between pig cardiomyocytes in the extent of t-tubule network, which correlated with cell size.
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Affiliation(s)
- Hanne C. Gadeberg
- Cardiovascular Research Laboratories, Bristol Cardiovascular, School of Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, BS8 1TD, United Kingdom
| | - Richard C. Bond
- Cardiovascular Research Laboratories, Bristol Cardiovascular, School of Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, BS8 1TD, United Kingdom
| | - Cherrie H. T. Kong
- Cardiovascular Research Laboratories, Bristol Cardiovascular, School of Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, BS8 1TD, United Kingdom
| | - Guillaume P. Chanoit
- School of Veterinary Sciences, University of Bristol, Langford House, Langford, BS40 5DU, United Kingdom
| | - Raimondo Ascione
- School of Clinical Sciences, University of Bristol, Bristol Royal Infirmary, Upper Maudlin Street, Bristol, BS2 8HW, United Kingdom
| | - Mark B. Cannell
- Cardiovascular Research Laboratories, Bristol Cardiovascular, School of Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, BS8 1TD, United Kingdom
- * E-mail: (AFJ); (MBC)
| | - Andrew F. James
- Cardiovascular Research Laboratories, Bristol Cardiovascular, School of Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, BS8 1TD, United Kingdom
- * E-mail: (AFJ); (MBC)
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18
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BIN1 regulates dynamic t-tubule membrane. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2015; 1863:1839-47. [PMID: 26578114 DOI: 10.1016/j.bbamcr.2015.11.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Revised: 10/31/2015] [Accepted: 11/09/2015] [Indexed: 11/23/2022]
Abstract
Cardiac transverse tubules (t-tubules) are specific membrane organelles critical in calcium signaling and excitation-contraction coupling required for beat-to-beat heart contraction. T-tubules are highly branched and form an interconnected network that penetrates the myocyte interior to form junctions with the sarcoplasmic reticulum. T-tubules are selectively enriched with specific ion channels and proteins crucial in calcium transient development necessary in excitation-contraction coupling, thus t-tubules are a key component of cardiac myocyte function. In this review, we focus primarily on two proteins concentrated within the t-tubular network, the L-type calcium channel (LTCC) and associated membrane anchor protein, bridging integrator 1 (BIN1). Here, we provide an overview of current knowledge in t-tubule morphology, composition, microdomains, as well as the dynamics of the t-tubule network. Secondly, we highlight multiple aspects of BIN1-dependent t-tubule function, which includes forward trafficking of LTCCs to t-tubules, LTCC clustering at t-tubule surface, microdomain organization and regulation at t-tubule membrane, and the formation of a slow diffusion barrier within t-tubules. Lastly, we describe progress in characterizing how acquired human heart failure can be attributed to abnormal BIN1 transcription and associated t-tubule remodeling. Understanding BIN1-regulated cardiac t-tubule biology in human heart failure management has the dual benefit of promoting progress in both biomarker development and therapeutic target identification. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.
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19
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Hoang-Trong TM, Ullah A, Jafri MS. Calcium Sparks in the Heart: Dynamics and Regulation. ACTA ACUST UNITED AC 2015; 6:203-214. [PMID: 27212876 DOI: 10.2147/rrb.s61495] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Calcium (Ca2+) plays a central role in the contraction of the heart. It is the bi-directional link between electrical excitation of the heart and contraction. Electrical excitation initiates Ca2+influx across the sarcolemma and T-tubular membrane that triggered calcium release from the sarcoplasmic reticulum. Ca2+sparks are the elementary events of calcium release from the sarcoplasmic reticulum. Therefore, understanding the dynamics of Ca2+sparks is essential for understanding the function of the heart. To this end, numerous experimental and computational studies have focused on this topic, exploring the mechanisms of calcium spark initiation, termination, and regulation and what role these play in normal and patho-physiology. The proper understanding of Ca2+ spark regulation and dynamics serves as the foundation for our insights into a multitude of pathological conditions may develop that can be the result of structural and/or functional changes at the cellular or subcellular level. Computational modeling of Ca2+ spark dynamics has proven to be a useful tool to understand Ca2+ spark dynamics. This review addresses our current understanding of Ca2+ sparks and how synchronized SR Ca2+ release, in which Ca2+ sparks is a major pathway, is linked to the different cardiac diseases, especially arrhythmias.
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Affiliation(s)
- Tuan M Hoang-Trong
- Department of Molecular Neuroscience, Krasnow Institute for Advanced Study, George Mason University, Fairfax, VA 22030
| | - Aman Ullah
- Department of Molecular Neuroscience, Krasnow Institute for Advanced Study, George Mason University, Fairfax, VA 22030
| | - M Saleet Jafri
- Department of Molecular Neuroscience, Krasnow Institute for Advanced Study, George Mason University, Fairfax, VA 22030; Biomedical Engineering and Technology, University of Maryland, Baltimore, MD 20201
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20
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Glukhov AV, Balycheva M, Sanchez-Alonso JL, Ilkan Z, Alvarez-Laviada A, Bhogal N, Diakonov I, Schobesberger S, Sikkel MB, Bhargava A, Faggian G, Punjabi PP, Houser SR, Gorelik J. Direct Evidence for Microdomain-Specific Localization and Remodeling of Functional L-Type Calcium Channels in Rat and Human Atrial Myocytes. Circulation 2015; 132:2372-84. [PMID: 26450916 PMCID: PMC4689179 DOI: 10.1161/circulationaha.115.018131] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Accepted: 10/02/2015] [Indexed: 12/27/2022]
Abstract
Supplemental Digital Content is available in the text. Distinct subpopulations of L-type calcium channels (LTCCs) with different functional properties exist in cardiomyocytes. Disruption of cellular structure may affect LTCC in a microdomain-specific manner and contribute to the pathophysiology of cardiac diseases, especially in cells lacking organized transverse tubules (T-tubules) such as atrial myocytes (AMs).
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Affiliation(s)
- Alexey V Glukhov
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Marina Balycheva
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Jose L Sanchez-Alonso
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Zeki Ilkan
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Anita Alvarez-Laviada
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Navneet Bhogal
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Ivan Diakonov
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Sophie Schobesberger
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Markus B Sikkel
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Anamika Bhargava
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Giuseppe Faggian
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Prakash P Punjabi
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Steven R Houser
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.)
| | - Julia Gorelik
- From Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, United Kingdom (A.V.G., M.B., J.L.S.-A., Z.I., A.A.-L., N.B., I.D., S.S., M.B.S., A.B., P.P.P., J.G.); University of Verona, School of Medicine, Verona, Italy (M.B., G.F.); Department of Cardiothoracic Surgery, Hammersmith Hospital, National Heart and Lung Institute, Imperial College London, United Kingdom (P.P.P.); and Cardiovascular Research Center and Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.R.H.).
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Pinali C, Kitmitto A. Serial block face scanning electron microscopy for the study of cardiac muscle ultrastructure at nanoscale resolutions. J Mol Cell Cardiol 2014; 76:1-11. [PMID: 25149127 DOI: 10.1016/j.yjmcc.2014.08.010] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2014] [Revised: 07/31/2014] [Accepted: 08/12/2014] [Indexed: 12/28/2022]
Abstract
Electron microscopy techniques have made a significant contribution towards understanding muscle physiology since the 1950s. Subsequent advances in hardware and software have led to major breakthroughs in terms of image resolution as well as the ability to generate three-dimensional (3D) data essential for linking structure to function and dysfunction. In this methodological review we consider the application of a relatively new technique, serial block face scanning electron microscopy (SBF-SEM), for the study of cardiac muscle morphology. Employing SBF-SEM we have generated 3D data for cardiac myocytes within the myocardium with a voxel size of ~15 nm in the X-Y plane and 50 nm in the Z-direction. We describe how SBF-SEM can be used in conjunction with selective staining techniques to reveal the 3D cellular organisation and the relationship between the t-tubule (t-t) and sarcoplasmic reticulum (SR) networks. These methods describe how SBF-SEM can be used to provide qualitative data to investigate the organisation of the dyad, a specialised calcium microdomain formed between the t-ts and the junctional portion of the SR (jSR). We further describe how image analysis methods may be applied to interrogate the 3D volumes to provide quantitative data such as the volume of the cell occupied by the t-t and SR membranes and the volumes and surface area of jSR patches. We consider the strengths and weaknesses of the SBF-SEM technique, pitfalls in sample preparation together with tips and methods for image analysis. By providing a 'big picture' view at high resolutions, in comparison to conventional confocal microscopy, SBF-SEM represents a paradigm shift for imaging cellular networks in their native environment.
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Affiliation(s)
- Christian Pinali
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, M13 9NT, UK
| | - Ashraf Kitmitto
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, M13 9NT, UK.
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Cannell MB, Kong CHT, Imtiaz MS, Laver DR. Control of sarcoplasmic reticulum Ca2+ release by stochastic RyR gating within a 3D model of the cardiac dyad and importance of induction decay for CICR termination. Biophys J 2013; 104:2149-59. [PMID: 23708355 DOI: 10.1016/j.bpj.2013.03.058] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 03/18/2013] [Accepted: 03/25/2013] [Indexed: 10/26/2022] Open
Abstract
The factors responsible for the regulation of regenerative calcium-induced calcium release (CICR) during Ca(2+) spark evolution remain unclear. Cardiac ryanodine receptor (RyR) gating in rats and sheep was recorded at physiological Ca(2+), Mg(2+), and ATP levels and incorporated into a 3D model of the cardiac dyad, which reproduced the time course of Ca(2+) sparks, Ca(2+) blinks, and Ca(2+) spark restitution. The termination of CICR by induction decay in the model principally arose from the steep Ca(2+) dependence of RyR closed time, with the measured sarcoplasmic reticulum (SR) lumen Ca(2+) dependence of RyR gating making almost no contribution. The start of CICR termination was strongly dependent on the extent of local depletion of junctional SR Ca(2+), as well as the time course of local Ca(2+) gradients within the junctional space. Reducing the dimensions of the dyad junction reduced Ca(2+) spark amplitude by reducing the strength of regenerative feedback within CICR. A refractory period for Ca(2+) spark initiation and subsequent Ca(2+) spark amplitude restitution arose from 1), the extent to which the regenerative phase of CICR can be supported by the partially depleted junctional SR, and 2), the availability of releasable Ca(2+) in the junctional SR. The physical organization of RyRs within the junctional space had minimal effects on Ca(2+) spark amplitude when more than nine RyRs were present. Spark amplitude had a nonlinear dependence on RyR single-channel Ca(2+) flux, and was approximately halved by reducing the flux from 0.6 to 0.2 pA. Although rat and sheep RyRs had quite different Ca(2+) sensitivities, Ca(2+) spark amplitude was hardly affected. This suggests that moderate changes in RyR gating by second-messenger systems will principally alter the spatiotemporal properties of SR release, with smaller effects on the amount released.
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Affiliation(s)
- M B Cannell
- Department of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
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Ferrantini C, Crocini C, Coppini R, Vanzi F, Tesi C, Cerbai E, Poggesi C, Pavone FS, Sacconi L. The transverse-axial tubular system of cardiomyocytes. Cell Mol Life Sci 2013; 70:4695-710. [PMID: 23846763 PMCID: PMC11113601 DOI: 10.1007/s00018-013-1410-5] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Revised: 06/03/2013] [Accepted: 06/13/2013] [Indexed: 10/26/2022]
Abstract
A characteristic histological feature of striated muscle cells is the presence of deep invaginations of the plasma membrane (sarcolemma), most commonly referred to as T-tubules or the transverse-axial tubular system (TATS). TATS mediates the rapid spread of the electrical signal (action potential) to the cell core triggering Ca(2+) release from the sarcoplasmic reticulum, ultimately inducing myofilament contraction (excitation-contraction coupling). T-tubules, first described in vertebrate skeletal muscle cells, have also been recognized for a long time in mammalian cardiac ventricular myocytes, with a structure and a function that in recent years have been shown to be far more complex and pivotal for cardiac function than initially thought. Renewed interest in T-tubule function stems from the loss and disorganization of T-tubules found in a number of pathological conditions including human heart failure (HF) and dilated and hypertrophic cardiomyopathies, as well as in animal models of HF, chronic ischemia and atrial fibrillation. Disease-related remodeling of the TATS leads to asynchronous and inhomogeneous Ca(2+)-release, due to the presence of orphan ryanodine receptors that have lost their coupling with the dihydropyridine receptors and are either not activated or activated with a delay. Here, we review the physiology of the TATS, focusing first on the relationship between function and structure, and then describing T-tubular remodeling and its reversal in disease settings and following effective therapeutic approaches.
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Affiliation(s)
- C. Ferrantini
- Division of Physiology, Department of Clinical and Experimental Medicine, University of Florence, Florence, Italy
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
| | - C. Crocini
- European Laboratory for Non-Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino, Italy
| | - R. Coppini
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
- Division of Pharmacology, Department “NeuroFarBa”, University of Florence, Florence, Italy
| | - F. Vanzi
- European Laboratory for Non-Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino, Italy
- Department of Biology, University of Florence, Florence, Italy
| | - C. Tesi
- Division of Physiology, Department of Clinical and Experimental Medicine, University of Florence, Florence, Italy
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
| | - E. Cerbai
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
- Division of Pharmacology, Department “NeuroFarBa”, University of Florence, Florence, Italy
| | - C. Poggesi
- Division of Physiology, Department of Clinical and Experimental Medicine, University of Florence, Florence, Italy
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
| | - F. S. Pavone
- European Laboratory for Non-Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino, Italy
- Department of Physics and Astronomy, University of Florence, Sesto Fiorentino, Italy
- National Institute of Optics (INO), National Research Council (CNR), Florence, Italy
| | - L. Sacconi
- European Laboratory for Non-Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino, Italy
- National Institute of Optics (INO), National Research Council (CNR), Florence, Italy
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Abstract
Ca(2+) waves were probably first observed in the early 1940s. Since then Ca(2+) waves have captured the attention of an eclectic mixture of mathematicians, neuroscientists, muscle physiologists, developmental biologists, and clinical cardiologists. This review discusses the current state of mathematical models of Ca(2+) waves, the normal physiological functions Ca(2+) waves might serve in cardiac cells, as well as how the spatial arrangement of Ca(2+) release channels shape Ca(2+) waves, and we introduce the idea of Ca(2+) phase waves that might provide a useful framework for understanding triggered arrhythmias.
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Affiliation(s)
- Leighton T Izu
- Department of Pharmacology, University of California, Davis, USA.
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Affiliation(s)
- Tobias Kohl
- Heart Research Center Goettingen, Niedersachsen, Germany
- Department of Cardiology and Pulmonology, University Medical Center Goettingen, Robert-Koch-Str. 40, 37075 Göttingen, Niedersachsen, Germany
| | - Stephan E. Lehnart
- Heart Research Center Goettingen, Niedersachsen, Germany
- Department of Cardiology and Pulmonology, University Medical Center Goettingen, Robert-Koch-Str. 40, 37075 Göttingen, Niedersachsen, Germany
- DZHK (German Centre for Cardiovascular Research) site Goettingen, Germany
- BioMET, Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, MD, USA
- Corresponding author. Tel: +49 551 39 10575; fax: +49 551 39 10650.
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Jayasinghe I, Crossman D, Soeller C, Cannell M. Comparison of the organization of T-tubules, sarcoplasmic reticulum and ryanodine receptors in rat and human ventricular myocardium. Clin Exp Pharmacol Physiol 2013; 39:469-76. [PMID: 21790719 DOI: 10.1111/j.1440-1681.2011.05578.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1. It is apparent from the literature that there are significant differences in excitation-contraction coupling between species, particularly in the density of calcium transporting proteins in the t-system and sarcoplasmic reticulum (SR) Ca(2+) release channels. Unfortunately, there is a lack of information as to how the principal structures that link electrical excitation to the activation of calcium-induced calcium release (CICR) are different between human and animal models (particularly rat). 2. Comparison of wheat germ agglutinin and caveolin-3 labelling revealed a non-uniform distribution of surface membrane glycosylation in the rat, rabbit and human, and that the rat t-system appeared more complex in geometry than the latter species. Analysis of the t-system skeleton showed that the t-system was highly branched in the rat compared with that of the human (0.8 ± 0.08 and 0.2 ± 0.07 branch points per μm(2) , respectively; P < 0.001). 3. We also compared the distribution of contractile machinery, sodium-calcium exchange, SR and ryanodine receptors (RyR) in rat and human. F-Actin and RyR labelling was used to estimate the area of contractile apparatus supplied by each RyR cluster. In the rat, each RyR cluster supplied an average cross-sectional area of contractile machinery of 0.36 ± 0.03μm(2) compared with 0.49 ± 0.04 μm(2) in human (P = 0.048). Sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA2a) labelling showed that the SR formed a tight network of loops surrounding contractile fibrils that were denser than the t-tubule network, but otherwise appeared similar in both species. 4. In general, the results show a higher density in structures involved in CICR in the rat compared with human.
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Affiliation(s)
- Id Jayasinghe
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
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Super-resolution imaging of EC coupling protein distribution in the heart. J Mol Cell Cardiol 2012; 58:32-40. [PMID: 23159441 DOI: 10.1016/j.yjmcc.2012.11.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Revised: 11/05/2012] [Accepted: 11/05/2012] [Indexed: 11/20/2022]
Abstract
The cardiac ryanodine receptor (RyR) plays a central role in the control of contractile function of the heart. In cardiac ventricular myocytes RyRs and associated Ca(2+) handling proteins, including membrane Ca(2+) channels, Ca(2+) pumps and other sarcolemmal and sarcoplasmic reticulum proteins interact to set the time course and amplitude of the electrically triggered cytosolic Ca(2+) transient. It has become increasingly clear that protein distribution and clustering on the nanometer scale is critical in determining the interaction of these proteins and the resulting properties of cardiac Ca(2+) handling. Such intricate near-molecular scale detail cannot be visualized with conventional fluorescence microscopy techniques (e.g. confocal microscopy) but it has recently become accessible with optical super-resolution techniques. These techniques retain the advantages of fluorescent marker technology, i.e. high specificity and excellent contrast, but have a spatial resolution approaching 10nm, i.e. objects not much further apart than 10nm can be distinguished, previously only attainable with electron microscopy. We review the use of these novel imaging techniques for the study of protein distribution in cardiac ventricular myocytes and discuss technical considerations as well as recent findings using super-resolution imaging. An emphasis is on single molecule localization based super-resolution approaches and their use to reveal the complexity of RyR cluster morphology, placement and relationship to other excitation-contraction coupling proteins. Super-resolution imaging approaches have already demonstrated their utility for the study of cardiac structure-function relationships and we anticipate that their use will rapidly increase and help improve our understanding of cardiac Ca(2+) regulation.
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Action potential propagation in transverse-axial tubular system is impaired in heart failure. Proc Natl Acad Sci U S A 2012; 109:5815-9. [PMID: 22451916 DOI: 10.1073/pnas.1120188109] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The plasma membrane of cardiac myocytes presents complex invaginations known as the transverse-axial tubular system (TATS). Despite TATS's crucial role in excitation-contraction coupling and morphological alterations found in pathological settings, TATS's electrical activity has never been directly investigated in remodeled tubular networks. Here we develop an ultrafast random access multiphoton microscope that, in combination with a customly synthesized voltage-sensitive dye, is used to simultaneously measure action potentials (APs) at multiple sites within the sarcolemma with submillisecond temporal and submicrometer spatial resolution in real time. We find that the tight electrical coupling between different sarcolemmal domains is guaranteed only within an intact tubular system. In fact, acute detachment by osmotic shock of most tubules from the surface sarcolemma prevents AP propagation not only in the disconnected tubules, but also in some of the tubules that remain connected with the surface. This indicates that a structural disorganization of the tubular system worsens the electrical coupling between the TATS and the surface. The pathological implications of this finding are investigated in failing hearts. We find that AP propagation into the pathologically remodeled TATS frequently fails and may be followed by local spontaneous electrical activity. Our findings provide insight on the relationship between abnormal TATS and asynchronous calcium release, a major determinant of cardiac contractile dysfunction and arrhythmias.
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Abreu-Velez AM, Howard MS, Jiao Z, Gao W, Yi H, Grossniklaus HE, Duque-Ramírez M, Dudley SC. Cardiac autoantibodies from patients affected by a new variant of endemic pemphigus foliaceus in Colombia, South America. J Clin Immunol 2011; 31:985-97. [PMID: 21796504 PMCID: PMC3380437 DOI: 10.1007/s10875-011-9574-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Accepted: 07/12/2011] [Indexed: 10/17/2022]
Abstract
Several patients affected by a new variant of endemic pemphigus foliaceus in El Bagre, Colombia (El Bagre-EPF) have experienced a sudden death syndrome, including persons below the age of 50. El Bagre-EPF patients share several autoantigens with paraneoplastic pemphigus patients, such as reactivity to plakins. Further, paraneoplastic pemphigus patients have autoantibodies to the heart. Therefore, we tested 15 El Bagre-EPF patients and 15 controls from the endemic area for autoreactivity to heart tissue using direct and indirect immunofluorescence, confocal microscopy, immunohistochemistry, immunoblotting, and immunoelectron microscopy utilizing heart extracts as antigens. We found that 7 of 15 El Bagre patients exhibited a polyclonal immune response to several cell junctions of the heart, often colocalizing with known markers. These colocalizing markers included those for the area composita of the heart, such as anti-desmoplakins I and II; markers for gap junctions, such as connexin 43; markers for tight junctions, such as ezrin and junctional adhesion molecule A; and adherens junctions, such pan-cadherin. We also detected colocalization of the patient antibodies within blood vessels, Purkinje fibers, and cardiac sarcomeres. We conclude that El Bagre-EPF patients display autoreactivity to multiple cardiac epitopes, that this disease may resemble what is found in patients with rheumatic carditis, and further, that the cardiac pathophysiology of this disorder warrants further evaluation.
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Crossman DJ, Ruygrok PR, Soeller C, Cannell MB. Changes in the organization of excitation-contraction coupling structures in failing human heart. PLoS One 2011; 6:e17901. [PMID: 21408028 PMCID: PMC3052389 DOI: 10.1371/journal.pone.0017901] [Citation(s) in RCA: 121] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2010] [Accepted: 02/14/2011] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND The cardiac myocyte t-tubular system ensures rapid, uniform cell activation and several experimental lines of evidence suggest changes in the t-tubular system and associated excitation-contraction coupling proteins may occur in heart failure. METHODS AND RESULTS The organization of t-tubules, L-type calcium channels (DHPRs), ryanodine receptors (RyRs) and contractile machinery were examined in fixed ventricular tissue samples from both normal and failing hearts (idiopathic (non-ischemic) dilated cardiomyopathy) using high resolution fluorescent imaging. Wheat germ agglutinin (WGA), Na-Ca exchanger, DHPR and caveolin-3 labels revealed a shift from a predominantly transverse orientation to oblique and axial directions in failing myocytes. In failure, dilation of peripheral t-tubules occurred and a change in the extent of protein glycosylation was evident. There was no change in the fractional area occupied by myofilaments (labeled with phalloidin) but there was a small reduction in the number of RyR clusters per unit area. The general relationship between DHPRs and RyR was not changed and RyR labeling overlapped with 51±3% of DHPR labeling in normal hearts. In longitudinal (but not transverse) sections there was an ∼30% reduction in the degree of colocalization between DHPRs and RyRs as measured by Pearson's correlation coefficient in failing hearts. CONCLUSIONS The results show that extensive remodelling of the t-tubular network and associated excitation-contraction coupling proteins occurs in failing human heart. These changes may contribute to abnormal calcium handling in heart failure. The general organization of the t-system and changes observed in failure samples have subtle differences to some animal models although the general direction of changes are generally similar.
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Affiliation(s)
- David J. Crossman
- Department of Physiology, Faculty of Medicine and Health Sciences, University of Auckland, Auckland, New Zealand
| | - Peter R. Ruygrok
- Department of Physiology, Faculty of Medicine and Health Sciences, University of Auckland, Auckland, New Zealand
- Auckland City Hospital, Auckland, New Zealand
| | - Christian Soeller
- Department of Physiology, Faculty of Medicine and Health Sciences, University of Auckland, Auckland, New Zealand
| | - Mark B. Cannell
- Department of Physiology, Faculty of Medicine and Health Sciences, University of Auckland, Auckland, New Zealand
- * E-mail:
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Peachey LD, Franzini‐Armstrong C. Structure and Function of Membrane Systems of Skeletal Muscle Cells. Compr Physiol 2011. [DOI: 10.1002/cphy.cp100102] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Atrial local Ca2+ signaling and inositol 1,4,5-trisphosphate receptors. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2010; 103:59-70. [DOI: 10.1016/j.pbiomolbio.2010.02.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2009] [Revised: 01/18/2010] [Accepted: 02/18/2010] [Indexed: 11/24/2022]
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Franzini-Armstrong C. STUDIES OF THE TRIAD : I. Structure of the Junction in Frog Twitch Fibers. ACTA ACUST UNITED AC 2010; 47:488-99. [PMID: 19866746 PMCID: PMC2108094 DOI: 10.1083/jcb.47.2.488] [Citation(s) in RCA: 286] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The structure of the junction between sarcoplasmic reticulum (SR) and transverse tubular (T) system at the triad has been studied in twitch fibers of the frog. The junction is formed by flattened surfaces of the SR lateral sacs and the T-system tubule, which face each other at a distance of 120–140 A. At periodic intervals of about 300 A, the SR membrane forms small projections, whose tips are joined to the T system membrane by some amorphous material. The SR projections and the amorphous material are here called SR feet. The feet are disposed in two parallel rows, two such rows being present on either side of the T-system tubule. The junctional area between the feet is apparently empty. The feet cover no more than 30% of the T system surface area and 3% of the total SR area. The functional significance of this interpretation of the junctional structure is discussed.
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Affiliation(s)
- C Franzini-Armstrong
- Departments of Physiology and Anatomy, Duke University Medical Center, Durham, North Carolina 27706
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There goes the neighborhood: pathological alterations in T-tubule morphology and consequences for cardiomyocyte Ca2+ handling. J Biomed Biotechnol 2010; 2010:503906. [PMID: 20396394 PMCID: PMC2852607 DOI: 10.1155/2010/503906] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2009] [Accepted: 01/15/2010] [Indexed: 12/19/2022] Open
Abstract
T-tubules are invaginations of the cardiomyocyte membrane into the cell interior which form a tortuous network. T-tubules provide proximity between the electrically excitable cell membrane and the sarcoplasmic reticulum, the main intracellular Ca2+ store. Tight coupling between the rapidly spreading action potential and Ca2+ release units in the SR membrane ensures synchronous Ca2+ release throughout the cardiomyocyte. This is a requirement for rapid and powerful contraction. In recent years, it has become clear that T-tubule structure and composition are altered in several pathological states which may importantly contribute to contractile defects in these conditions. In this review, we describe the “neighborhood” of proteins in the dyadic cleft which locally controls cardiomyocyte Ca2+ homeostasis and how alterations in T-tubule structure and composition may alter this neighborhood during heart failure, atrial fibrillation, and diabetic cardiomyopathy. Based on this evidence, we propose that T-tubules have the potential to serve as novel therapeutic targets.
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Jayasinghe I, Cannell MB, Soeller C. Organization of ryanodine receptors, transverse tubules, and sodium-calcium exchanger in rat myocytes. Biophys J 2009; 97:2664-73. [PMID: 19917219 PMCID: PMC2776253 DOI: 10.1016/j.bpj.2009.08.036] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2009] [Revised: 08/12/2009] [Accepted: 08/13/2009] [Indexed: 10/20/2022] Open
Abstract
Confocal and total internal reflection fluorescence imaging was used to examine the distribution of caveolin-3, sodium-calcium exchange (NCX) and ryanodine receptors (RyRs) in rat ventricular myocytes. Transverse and longitudinal optical sectioning shows that NCX is distributed widely along the transverse and longitudinal tubular system (t-system). The NCX labeling consisted of both punctate and distributed components, which partially colocalize with RyRs (27%). Surface membrane labeling showed a similar pattern but the fraction of RyR clusters containing NCX label was decreased and no nonpunctate labeling was observed. Sixteen percent of RyRs were not colocalized with the t-system and 1.6% of RyRs were found on longitudinal elements of the t-system. The surface distribution of RyR labeling was not generally consistent with circular patches of RyRs. This suggests that previous estimates for the number of RyRs in a junction (based on circular close-packed arrays) need to be revised. The observed distribution of caveolin-3 labeling was consistent with its exclusion from RyR clusters. Distance maps for all colocalization pairs were calculated to give the distance between centroids of punctate labeling and edges for distributed components. The possible roles for punctate NCX labeling are discussed.
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Affiliation(s)
- Izzy Jayasinghe
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Mark B. Cannell
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Christian Soeller
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
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Woo SH, Risius T, Morad M. Modulation of local Ca2+ release sites by rapid fluid puffing in rat atrial myocytes. Cell Calcium 2006; 41:397-403. [PMID: 17087992 PMCID: PMC1894949 DOI: 10.1016/j.ceca.2006.09.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2006] [Revised: 08/29/2006] [Accepted: 09/04/2006] [Indexed: 11/17/2022]
Abstract
Atrial myocytes that lack t-tubules appear to have two functionally separate sarcoplasmic Ca2+ stores: a peripheral store associated with plasmalemmal L-type calcium channels and a central store with no apparent proximity to L-type calcium channels. Here we describe a set of calcium sparks and waves that are triggered by puffing of pressurized (200-400 mmH2O) bathing solutions onto resting isolated rat atrial myocytes. Puffing of pressurized (200 mmH2O) solutions, identical to those bathing the myocytes from distances of approximately 150 microm onto the surface of a single myocyte triggered or enhanced spontaneously occurring peripheral sparks by five- to six-fold and central Ca2+ sparks by two- to three-fold, without altering the unitary spark properties. Exposure to higher pressure flows (400 mmH2O) often triggered longitudinally spreading Ca2+ waves. These results suggest that pressurized flows may directly modulate Ca2+ signaling of atrial myocytes by activating the intracellular Ca2+ release sites.
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Affiliation(s)
- Sun-Hee Woo
- College of Pharmacy, Chungnam National University, 220 Gung-Dong, Daejeon, 305-764 Korea
| | - Tim Risius
- Department of Pharmacology, Georgetown University Medical Center, 3900 Reservoir Road, NW, Washington DC, 20057 USA
| | - Martin Morad
- Department of Pharmacology, Georgetown University Medical Center, 3900 Reservoir Road, NW, Washington DC, 20057 USA
- *Corresponding author: Martin Morad, Department of Pharmacology, Georgetown University Medical Center, 3900 Reservoir Road NW, Washington DC 20057, USA, Tel: +1 202 687 8440, Fax: +1 202 687 8453,
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Woo SH, Cleemann L, Morad M. Diversity of atrial local Ca2+ signalling: evidence from 2-D confocal imaging in Ca2+-buffered rat atrial myocytes. J Physiol 2005; 567:905-21. [PMID: 16020459 PMCID: PMC1474227 DOI: 10.1113/jphysiol.2005.092270] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Atrial myocytes, lacking t-tubules, have two functionally separate groups of ryanodine receptors (RyRs): those at the periphery colocalized with dihydropyridine receptors (DHPRs), and those at the cell interior not associated with DHPRs. We have previously shown that the Ca(2+) current (I(Ca))-gated central Ca(2+) release has a fast component that is followed by a slower and delayed rising phase. The mechanisms that regulate the central Ca(2+) releases remain poorly understood. The fast central release component is highly resistant to dialysed Ca(2+) buffers, while the slower, delayed component is completely suppressed by such exogenous buffers. Here we used dialysis of Ca(2+) buffers (EGTA) into voltage-clamped rat atrial myocytes to isolate the fast component of central Ca(2+) release and examine its properties using rapid (240 Hz) two-dimensional confocal Ca(2+) imaging. We found two populations of rat atrial myocytes with respect to the ratio of central to peripheral Ca(2+) release (R(c/p)). In one population ('group 1', approximately 60% of cells), R(c/p) converged on 0.2, while in another population ('group 2', approximately 40%), R(c/p) had a Gaussian distribution with a mean value of 0.625. The fast central release component of group 2 cells appeared to result from in-focus Ca(2+) sparks on activation of I(Ca). In group 1 cells intracellular membranes associated with t-tubular structures were never seen using short exposures to membrane dyes. In most of the group 2 cells, a faint intracellular membrane staining was observed. Quantification of caffeine-releasable Ca(2+) pools consistently showed larger central Ca(2+) stores in group 2 and larger peripheral stores in group 1 cells. The R(c/p) was larger at more positive and negative voltages in group 1 cells. In contrast, in group 2 cells, the R(c/p) was constant at all voltages. In group 1 cells the gain of peripheral Ca(2+) release sites (Delta[Ca(2+)]/I(Ca)) was larger at -30 than at +20 mV, but significantly dampened at the central sites. On the other hand, the gains of peripheral and central Ca(2+) releases in group 2 cells showed no voltage dependence. Surprisingly, the voltage dependence of the fast central release component was bell-shaped and similar to that of I(Ca) in both cell groups. Removal of extracellular Ca(2+) or application of Ni(2+) (5 mM) suppressed equally I(Ca) and Ca(2+) release from the central release sites at +60 mV. Depolarization to +100 mV, where I(Ca) is absent and the Na(+)-Ca(2+) exchanger (NCX) acts in reverse mode, did not trigger the fast central Ca(2+) releases in either group, but brief reduction of [Na(+)](o) to levels equivalent to [Na(+)](i) facilitated fast peripheral and central Ca(2+) releases in group 2 myocytes, but not in group 1 myocytes. In group 2 cells, long-lasting (> 1 min) exposures to caffeine (10 mM) or ryanodine (20 microM) significantly suppressed I(Ca)-triggered central and peripheral Ca(2+) releases. Our data suggest significant diversity of local Ca(2+) signalling in rat atrial myocytes. In one group, I(Ca)-triggered peripheral Ca(2+) release propagates into the interior triggering central Ca(2+) release with significant delay. In a second group of myocytes I(Ca) triggers a significant number of central sites as rapidly and effectively as the peripheral sites, thereby producing more synchronized Ca(2+) releases throughout the myocytes. The possible presence of vestigial t-tubules and larger Ca(2+) content of central sarcoplasmic reticulum (SR) in group 2 cells may be responsible for the rapid and strong activation of central release of Ca(2+) in this subset of atrial myocytes.
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Affiliation(s)
- Sun-Hee Woo
- Department of Pharmacology, Georgetown University Medical Center, Washington, DC 20057, USA
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Rasmussen HB, Møller M, Knaus HG, Jensen BS, Olesen SP, Jørgensen NK. Subcellular localization of the delayed rectifier K+channels KCNQ1 and ERG1 in the rat heart. Am J Physiol Heart Circ Physiol 2004; 286:H1300-9. [PMID: 14670813 DOI: 10.1152/ajpheart.00344.2003] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the heart, several K+channels are responsible for the repolarization of the cardiac action potential, including transient outward and delayed rectifier K+currents. In the present study, the cellular and subcellular localization of the two delayed rectifier K+channels, KCNQ1 and ether- a- go- go-related gene-1 (ERG1), was investigated in the adult rat heart. Confocal immunofluorescence microscopy of atrial and ventricular cells revealed that whereas KCNQ1 labeling was detected in both the peripheral sarcolemma and a structure transversing the myocytes, ERG1 immunoreactivity was confined to the latter. Immunoelectron microscopy of atrial and ventricular myocytes showed that the ERG1 channel was primarily expressed in the transverse tubular system and its entrance, whereas KCNQ1 was detected in both the peripheral sarcolemma and in the T tubules. Thus, whereas ERG1 displays a very restricted subcellular localization pattern, KCNQ1 is more widely distributed within the cardiac cells. The localization of these K+channels to the transverse tubular system close to the Ca2+channels renders them with maximal repolarizing effect.
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Affiliation(s)
- Hanne Borger Rasmussen
- Department of Medical Physiology and Copenhagen Heart Research, University of Copenhagen, The Panum Institute, DK-2200 Copenhagen N, Denmark.
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Antunes-Rodrigues J, de Castro M, Elias LLK, Valença MM, McCann SM. Neuroendocrine control of body fluid metabolism. Physiol Rev 2004; 84:169-208. [PMID: 14715914 DOI: 10.1152/physrev.00017.2003] [Citation(s) in RCA: 311] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Mammals control the volume and osmolality of their body fluids from stimuli that arise from both the intracellular and extracellular fluid compartments. These stimuli are sensed by two kinds of receptors: osmoreceptor-Na+ receptors and volume or pressure receptors. This information is conveyed to specific areas of the central nervous system responsible for an integrated response, which depends on the integrity of the anteroventral region of the third ventricle, e.g., organum vasculosum of the lamina terminalis, median preoptic nucleus, and subfornical organ. The hypothalamo-neurohypophysial system plays a fundamental role in the maintenance of body fluid homeostasis by secreting vasopressin and oxytocin in response to osmotic and nonosmotic stimuli. Since the discovery of the atrial natriuretic peptide (ANP), a large number of publications have demonstrated that this peptide provides a potent defense mechanism against volume overload in mammals, including humans. ANP is mostly localized in the heart, but ANP and its receptor are also found in hypothalamic and brain stem areas involved in body fluid volume and blood pressure regulation. Blood volume expansion acts not only directly on the heart, by stretch of atrial myocytes to increase the release of ANP, but also on the brain ANPergic neurons through afferent inputs from baroreceptors. Angiotensin II also plays an important role in the regulation of body fluids, being a potent inducer of thirst and, in general, antagonizes the actions of ANP. This review emphasizes the role played by brain ANP and its interaction with neurohypophysial hormones in the control of body fluid homeostasis.
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Affiliation(s)
- José Antunes-Rodrigues
- Department of Physiology, School of Medicine of Ribeirao Preto, University of São Paulo, Ribeirao Preto, São Paulo, Brazil.
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41
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Kirk MM, Izu LT, Chen-Izu Y, McCulle SL, Wier WG, Balke CW, Shorofsky SR. Role of the transverse-axial tubule system in generating calcium sparks and calcium transients in rat atrial myocytes. J Physiol 2003; 547:441-51. [PMID: 12562899 PMCID: PMC2342655 DOI: 10.1113/jphysiol.2002.034355] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2002] [Accepted: 11/27/2002] [Indexed: 11/08/2022] Open
Abstract
Cardiac atrial cells lack a regular system of transverse tubules like that in cardiac ventricular cells. Nevertheless, many atrial cells do possess an irregular internal transverse-axial tubular system (TATS). To investigate the possible role of the TATS in excitation-contraction coupling in atrial myocytes, we visualized the TATS (labelled with the fluorescent indicator, Di-8-ANEPPS) simultaneously with Ca2+ transients and/or Ca2+ sparks (fluo-4). In confocal transverse linescan images of field-stimulated cells, whole-cell Ca2+ transients had two morphologies: 'U-shaped' transients and irregular or 'W-shaped' transients with a varying number of points of origin of the Ca2+ transient. About half (54 %, n =289 cells, 13 animals) of the cells had a TATS. Cells with TATS had a larger mean diameter (13.2 +/- 2.8 microm) than cells without TATS (11.7 +/- 2.0 microm) and were more common in the left atrium (n = 206 cells; left atrium: 76 with TATS, 30 without TATS; right atrium: 42 with TATS, 58 without TATS). Simultaneous measurement of Ca2+ sparks and sarcolemmal structures showed that cells without TATS had U-shaped transients that started at the cell periphery, and cells with TATS had W-shaped transients that began simultaneously at the cell periphery and the TATS. Most (82 out of 102 from 31 cells) 'spontaneous' (non-depolarized) Ca2+ sparks occurred within 1 microm of a sarcolemmal structure (cell periphery or TATS), and 33 % occurred within 1 pixel (0.125 microm). We conclude that the presence of a sarcolemmal membrane either at the cell periphery or in the TATS in close apposition to the sarcoplasmic reticulum is required for the initiation of an evoked Ca2+ transient and for spontaneous Ca2+ sparks.
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Affiliation(s)
- Malcolm M Kirk
- Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201-1541, USA
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Woo SH, Cleemann L, Morad M. Ca2+ current-gated focal and local Ca2+ release in rat atrial myocytes: evidence from rapid 2-D confocal imaging. J Physiol 2002; 543:439-53. [PMID: 12205180 PMCID: PMC2290519 DOI: 10.1113/jphysiol.2002.024190] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In atrial myocytes immunocytochemistry has shown two groups of ryanodine receptors (RyRs): those at the periphery colocalized with dihydropyridine receptors (DHPRs) and those at the cell interior not associated with DHPRs. The extent to which the two sets of RyRs are controlled by Ca2+ current (I(Ca)) or Ca2+ diffusion remains to be determined. Here, using rapid (240 Hz) two-dimensional confocal Ca2+ imaging in rat atrial myocytes, we examine directly the role of I(Ca) on the two-dimensional patterns of local and focal Ca2+ releases. I(Ca) evoked peripheral Ca2+ release within 1-4 ms, causing a rapid monophasic local rise of Ca2+, which then propagated into the cell interior along sarcomeric lines (approximately 2 microm) with a velocity of approximately 230 microm s(-1), even though we found no evidence for organized t-tubules using di-8-ANEPPS staining. I(Ca)-triggered Ca2+ release in the cell centre, on the other hand, had both a rapid (12 ms) and slower delayed components (12-50 ms). The voltage dependence of peripheral Ca2+ release and the two components of central release was bell shaped, and the magnitude of each release component was linearly related to I(Ca). Premature termination (2-10 ms) of I(Ca) was equally effective in abbreviating both the peripheral and slow central Ca2+ release. High concentration of Ca2+ buffers (2-5 mM EGTA plus 1 mM fluo-3) completely abolished the I(Ca)-gated propagation wave and the slow delayed component of Ca2+ release, but had little or no effect on the rapid component of central release. The efficacy of I(Ca) to trigger Ca2+ release in periphery of the myocyte was approximately 5 times higher than in the centre, consistent with the smaller measured central Ca2+ release. The quantification of central Ca2+ release as a function of peripheral release suggests a cooperative gating mechanism(s) for central release. These findings indicate that both I(Ca) and diffusion of Ca2+ from the peripheral sites contribute to the gating of Ca2+ release from central SR. How in fact the I(Ca)-dependent fast component of central release is activated remains to be determined.
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Affiliation(s)
- Sun-Hee Woo
- Department of Pharmacology, Georgetown University Medical Center, 3900 Reservoir Road NW, Washington, DC 20007, USA
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Jones SA, Morton MJ, Hunter M, Boyett MR. Expression of TASK-1, a pH-sensitive twin-pore domain K(+) channel, in rat myocytes. Am J Physiol Heart Circ Physiol 2002; 283:H181-5. [PMID: 12063289 DOI: 10.1152/ajpheart.00963.2001] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have investigated the expression of TASK-1, a pH-sensitive, twin-pore domain K(+) channel in the rat heart. A mammalian cell line of Chinese hamster ovary cells (CHO), transfected with a plasmid containing mouse TASK-1, demonstrated the specificity of the anti-TASK-1 antibody. TASK-1 expression in cardiac tissue was initially demonstrated by Western blot and then localized by immunofluorescence. In single rat ventricular myocytes, strong staining of the TASK-1 protein was located at the intercalated disks and across the cell in a striated pattern, corresponding to the transverse axial tubular network (T tubules). In contrast, single rat atrial myocytes were stained at the intercalated disks with a weak punctate, striated pattern corresponding to underdeveloped T tubules. Also, formamide was used to induce the detubulation of ventricular myocytes, which enabled confirmation that TASK-1 protein expression occurs in T tubules. Consistent with this, RT-PCR revealed the expression of TASK-1 mRNA in total RNA from both the ventricles and atria. In this study, we conclusively demonstrated that TASK-1 protein and mRNA were expressed in rat atrial and ventricular tissue. The extensive distribution of TASK-1 shown to exist within myocyte membranes may provide a potential future target for antiarrhythmic drugs.
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Affiliation(s)
- Sandra A Jones
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom.
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Musa H, Lei M, Honjo H, Jones SA, Dobrzynski H, Lancaster MK, Takagishi Y, Henderson Z, Kodama I, Boyett MR. Heterogeneous expression of Ca(2+) handling proteins in rabbit sinoatrial node. J Histochem Cytochem 2002; 50:311-24. [PMID: 11850434 DOI: 10.1177/002215540205000303] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
We investigated the densities of the L-type Ca(2+) current, i(Ca,L), and various Ca(2+) handling proteins in rabbit sinoatrial (SA) node. The density of i(Ca,L), recorded with the whole-cell patch-clamp technique, varied widely in sinoatrial node cells. The density of i(Ca,L) was significantly (p<0.001) correlated with cell capacitance (measure of cell size) and the density was greater in larger cells (likely to be from the periphery of the SA node) than in smaller cells (likely to be from the center of the SA node). Immunocytochemical labeling of the L-type Ca(2+) channel, Na(+)-Ca(2+) exchanger, sarcoplasmic reticulum Ca(2+) release channel (RYR2), and sarcoplasmic reticulum Ca(2+) pump (SERCA2) also varied widely in SA node cells. In all cases there was significantly (p<0.05) denser labeling of cells from the periphery of the SA node than of cells from the center. In contrast, immunocytochemical labeling of the Na(+)-K(+) pump was similar in peripheral and central cells. We conclude that Ca(2+) handling proteins are sparse and poorly organized in the center of the SA node (normally the leading pacemaker site), whereas they are more abundant in the periphery (at the border of the SA node with the surrounding atrial muscle).
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Affiliation(s)
- Hanny Musa
- School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
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45
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Scriven DR, Dan P, Moore ED. Distribution of proteins implicated in excitation-contraction coupling in rat ventricular myocytes. Biophys J 2000; 79:2682-91. [PMID: 11053140 PMCID: PMC1301148 DOI: 10.1016/s0006-3495(00)76506-4] [Citation(s) in RCA: 256] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
We have examined the distribution of ryanodine receptors, L-type Ca(2+) channels, calsequestrin, Na(+)/Ca(2+) exchangers, and voltage-gated Na(+) channels in adult rat ventricular myocytes. Enzymatically dissociated cells were fixed and dual-labeled with specific antibodies using standard immunocytochemistry protocols. Images were deconvolved to reverse the optical distortion produced by wide-field microscopes equipped with high numerical aperture objectives. Every image showed a well-ordered array of fluorescent spots, indicating that all of the proteins examined were distributed in discrete clusters throughout the cell. Mathematical analysis of the images revealed that dyads contained only ryanodine receptors, L-type Ca(2+) channels, and calsequestrin, and excluded Na(+)/Ca(2+) exchangers and voltage-gated Na(+) channels. The Na(+)/Ca(2+) exchanger and voltage-gated Na(+) channels were distributed largely within the t-tubules, on both transverse and axial elements, but were not co-localized. The t-tubule can therefore be subdivided into at least three structural domains; one of coupling (dyads), one containing the Na(+)/Ca(2+) exchanger, and one containing voltage-gated Na(+) channels. We conclude that if either the slip mode conductance of the Na(+) channel or the reverse mode of the Na(+)/Ca(2+) exchanger are to contribute to the contractile force, the fuzzy space must extend outside of the dyad.
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Affiliation(s)
- D R Scriven
- Department of Physiology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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Takeuchi S, Takagishi Y, Yasui K, Murata Y, Toyama J, Kodama I. Voltage-gated K(+)Channel, Kv4.2, localizes predominantly to the transverse-axial tubular system of the rat myocyte. J Mol Cell Cardiol 2000; 32:1361-9. [PMID: 10860776 DOI: 10.1006/jmcc.2000.1172] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Kv4.2 subunit, a member of K(+)channel gene family, is considered to play a major role in the formation of depolarization-activated transient outward K(+)current channels in the mammalian heart. We investigated the subcellular localization of Kv4.2 subunit in the rat heart by immunofluorescence and immunoelectron microscopy. In atrial cells, Kv4.2 immunofluorescent staining was intensely observed in the peripheral sarcolemma and the intercalated disks, but seldom found in transverse tubules, which are rare or absent in atrial cells. In ventricular cells, the labeling of Kv4.2 immunofluorescent staining was found throughout the entire cell membrane, and the staining was stronger in the transverse-axial tubular system than in the peripheral sarcolemma. Correlative immunoconfocal and immunoelectron microscopy using FluoroNanogold confirmed that Kv4.2 distributed in the transverse-axial tubular system including the longitudinally oriented axial tubules. Immunogold electron microscopy of ultrathin cryosections revealed that Kv4.2 was distributed on the plasma membranes of the T-tubules. The extensive distribution of Kv4.2 on the entire cell membrane of myocytes would provide rat myocardial cells with a large capability for the transport of K(+)ions through the channels in the repolarization phase.
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Affiliation(s)
- S Takeuchi
- Department of Circulation, Nagoya University, Nagoya, Japan
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Sham JS, Song LS, Chen Y, Deng LH, Stern MD, Lakatta EG, Cheng H. Termination of Ca2+ release by a local inactivation of ryanodine receptors in cardiac myocytes. Proc Natl Acad Sci U S A 1998; 95:15096-101. [PMID: 9844021 PMCID: PMC24581 DOI: 10.1073/pnas.95.25.15096] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In heart, a robust regulatory mechanism is required to counteract the regenerative Ca2+-induced Ca2+ release from the sarcoplasmic reticulum. Several mechanisms, including inactivation, adaptation, and stochastic closing of ryanodine receptors (RyRs) have been proposed, but no conclusive evidence has yet been provided. We probed the termination process of Ca2+ release by using a technique of imaging local Ca2+ release, or "Ca2+ spikes", at subcellular sites; and we tracked the kinetics of Ca2+ release triggered by L-type Ca2+ channels. At 0 mV, Ca2+ release occurred and terminated within 40 ms after the onset of clamp pulses (0 mV). Increasing the open-duration and promoting the reopenings of Ca2+ channels with the Ca2+ channel agonist, FPL64176, did not prolong or trigger secondary Ca2+ spikes, even though two-thirds of the sarcoplasmic reticulum Ca2+ remained available for release. Latency of Ca2+ spikes coincided with the first openings but not with the reopenings of L-type Ca2+ channels. After an initial maximal release, even a multi-fold increase in unitary Ca2+ current induced by a hyperpolarization to -120 mV failed to trigger additional release, indicating absolute refractoriness of RyRs. When the release was submaximal (e.g., at +30 mV), tail currents did activate additional Ca2+ spikes; confocal images revealed that they originated from RyRs unfired during depolarization. These results indicate that Ca2+ release is terminated primarily by a highly localized, use-dependent inactivation of RyRs but not by the stochastic closing or adaptation of RyRs in intact ventricular myocytes.
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Affiliation(s)
- J S Sham
- Division of Pulmonary and Critical Care Medicine, The Johns Hopkins Medical Institutions, Baltimore, MD 21224, USA.
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48
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Soeller C, Cannell MB. Numerical simulation of local calcium movements during L-type calcium channel gating in the cardiac diad. Biophys J 1997; 73:97-111. [PMID: 9199775 PMCID: PMC1180912 DOI: 10.1016/s0006-3495(97)78051-2] [Citation(s) in RCA: 139] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Computer simulation was used to investigate the calcium levels after sarcolemmal calcium influx through L-type calcium channels (DHPRs) into the narrow diadic space of cardiac muscle. The effect of various cytosolic and membranebound buffers, diad geometry, DHPR properties (open time and current), and surface charge were examined. The simulations showed that phospholipid binding sites on the sarcolemmal membrane are the major buffer affecting free calcium ([Ca2+]) levels in the diad. The inclusion of surface charge effects calculated from Gouy-Chapman theory resulted in a marked decrease in [Ca2+] levels at all times and a faster decay of [Ca2+] after termination of DHPR influx. For a DHPR current of 200 fA, [Ca2+] at the center of the diad reached peak levels of approximately 73 microM. In larger diads (> or = 400 nm diameter), [Ca2+] decayed more slowly than in smaller diads (100-200 nm diameter), although peak [Ca2+] levels reached during typical DHPR open times were similar. For a wide range of DHPR single-channel current magnitudes (Ica = 25-200 fA), [Ca2+] levels in the diad were approximately proportional to ICa. The decrease in calculated [Ca2+] levels due to the effects of surface charge can be interpreted as resulting from an effective "volume expansion" of the diad space. Furthermore, the layer of increased [Ca2+] close to the sarcolemmal membrane can act as a fast buffer.
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Affiliation(s)
- C Soeller
- Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London, England
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Yamasaki Y, Furuya Y, Araki K, Matsuura K, Kobayashi M, Ogata T. Ultra-high-resolution scanning electron microscopy of the sarcoplasmic reticulum of the rat atrial myocardial cells. Anat Rec (Hoboken) 1997; 248:70-5. [PMID: 9143669 DOI: 10.1002/(sici)1097-0185(199705)248:1<70::aid-ar8>3.0.co;2-j] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND The sarcoplasmic reticulum (SR) of mammalian ventricular and atrial muscles share common features but also differ because T-tubules are rare and extended junctional SR is exclusively seen in the atrium. This scanning electron microscope (SEM) study was undertaken to clarify the three-dimensional organization of the rat atrial SR system. Specific preparations were examined with an ultra-high-resolution SEM. METHODS Fixed right rat atria were frozen, fractured, and macerated by the aldehyde-osmium-DMSO-osmium method to remove myofibrils and cytoplasmic matrix. Left exposed were mitochondria, SR, and sarcolemma. Dried specimens were then impregnated by osmium-hydrazine and examined without metal coating. RESULTS In place of conventional T-tubules, a prominent type of sarcotubules, Z-tubules, were found at the Z-line level. Branches from these tubules joined the cisternal SR, which was 100-300 nm in diameter and localized near the Z-line, and formed extensive SR meshworks and polygonal patches. Bulbous swellings, the corbular SR, were also evident. Sarcotubular reticulum completely surrounded each myofibril. The intermyofibrillar SR, especially Z-tubules, joined the peripheral subsarcolemmal SR, which was also arranged as a meshwork and was closely apposed to the sarcolemma. CONCLUSIONS These SEM observations confirm the organization of the rat atrial SR system and present new, detailed, three-dimensional images of Z-tubules, cisternal SR, extended junctional SR, and peripheral SR, which provide further structural insight.
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Affiliation(s)
- Y Yamasaki
- Department of Surgery, Kochi Medical School, Japan
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50
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Skepper JN, Navaratnam V. Ultrastructural features of left ventricular myocytes in active and torpid hamsters compared with rats: a morphometric study. J Anat 1995; 186 ( Pt 3):585-92. [PMID: 7559131 PMCID: PMC1167016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Myocytes from the midmyocardium of the left ventricle of rats and hamsters were examined by transmission electron microscopy. The volume fraction of lipid droplets in such myocytes was about 6 times greater in the active hamster than in the rat, but it became progressively reduced during cold exposure and entry into hibernation to values similar to those of the rat. The volume fraction of the T-system as well as the surface density of its membranes were each found to be twice as large in hamster myocytes as in the rat but there was no difference in these parameters between control, cold-exposed and torpid hamsters. The surface density of the junctional sarcoplasmic reticulum coupled with elements of the T-system was greater in active hamsters when compared with those of the rat, and greater still in torpid hamsters. There was no significant difference in the surface density of free sarcoplasmic reticulum between control hamsters, cold-exposed hamsters and rats but it was almost doubled in torpid hamsters. It is proposed that these features represent inherent differences in the ultrastructure of the left ventricle between the rat and hamster that may facilitate entry into hibernation. Additionally, further structural modifications during entry into hibernation may be related to alterations in lipid metabolism and modifications of calcium handling.
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Affiliation(s)
- J N Skepper
- Department of Anatomy, University of Cambridge, UK
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