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Power A, Kaur S, Dyer C, Ward ML. Disruption of Transverse-Tubules Eliminates the Slow Force Response to Stretch in Isolated Rat Trabeculae. Front Physiol 2020; 11:193. [PMID: 32210837 PMCID: PMC7069251 DOI: 10.3389/fphys.2020.00193] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 02/19/2020] [Indexed: 12/15/2022] Open
Abstract
Ventricular muscle has a biphasic response to stretch. There is an immediate increase in force that coincides with the stretch which is followed by a second phase that takes several minutes for force to develop to a new steady state. The initial increase in force is due to changes in myofilament properties, whereas the second, slower component of the stretch response (known as the “slow force response” or SFR) is accompanied by a steady increase in Ca2+ transient amplitude. Evidence shows stretch-dependent Ca2+ influx during the SFR occurs through some mechanism that is continuously active for several minutes following stretch. Many of the candidate ion channels are located primarily in the t-tubules, which are consequently lost in heart disease. Our aim, therefore, was to investigate the impact of t-tubule loss on the SFR in non-failing cardiac trabeculae in which expression of the different Ca2+ handling proteins was not altered by any disease process. For comparison, we also investigated the effect of formamide detubulation of trabeculae on β-adrenergic activation (1 μM isoproterenol), since this is another key regulator of cardiac force. Measurement of intracellular calcium ([Ca2+]i) and isometric stress were made in RV trabeculae from rat hearts before, during and after formamide treatment (1.5 M for 5 min), which on washout seals the surface sarcolemmal t-tubule openings. Results showed detubulation slowed the time course of Ca2+ transients and twitch force, with time-to-peak, maximum rate-of-rise, and relaxation prolonged in trabeculae at optimal length (Lo). Formamide treatment also prevented development of the SFR following a step change in length from 90 to 100% Lo, and blunted the response to β-adrenergic activation (1 μM isoproterenol).
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Affiliation(s)
- Amelia Power
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
| | - Sarbjot Kaur
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
| | - Cameron Dyer
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
| | - Marie-Louise Ward
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
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2
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Johnson DM, Antoons G. Arrhythmogenic Mechanisms in Heart Failure: Linking β-Adrenergic Stimulation, Stretch, and Calcium. Front Physiol 2018; 9:1453. [PMID: 30374311 PMCID: PMC6196916 DOI: 10.3389/fphys.2018.01453] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Accepted: 09/25/2018] [Indexed: 12/22/2022] Open
Abstract
Heart failure (HF) is associated with elevated sympathetic tone and mechanical load. Both systems activate signaling transduction pathways that increase cardiac output, but eventually become part of the disease process itself leading to further worsening of cardiac function. These alterations can adversely contribute to electrical instability, at least in part due to the modulation of Ca2+ handling at the level of the single cardiac myocyte. The major aim of this review is to provide a definitive overview of the links and cross talk between β-adrenergic stimulation, mechanical load, and arrhythmogenesis in the setting of HF. We will initially review the role of Ca2+ in the induction of both early and delayed afterdepolarizations, the role that β-adrenergic stimulation plays in the initiation of these and how the propensity for these may be altered in HF. We will then go onto reviewing the current data with regards to the link between mechanical load and afterdepolarizations, the associated mechano-sensitivity of the ryanodine receptor and other stretch activated channels that may be associated with HF-associated arrhythmias. Furthermore, we will discuss how alterations in local Ca2+ microdomains during the remodeling process associated the HF may contribute to the increased disposition for β-adrenergic or stretch induced arrhythmogenic triggers. Finally, the potential mechanisms linking β-adrenergic stimulation and mechanical stretch will be clarified, with the aim of finding common modalities of arrhythmogenesis that could be targeted by novel therapeutic agents in the setting of HF.
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Affiliation(s)
- Daniel M Johnson
- Department of Cardiothoracic Surgery, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, Netherlands
| | - Gudrun Antoons
- Department of Physiology, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, Netherlands
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3
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Radwański PB, Johnson CN, Györke S, Veeraraghavan R. Cardiac Arrhythmias as Manifestations of Nanopathies: An Emerging View. Front Physiol 2018; 9:1228. [PMID: 30233404 PMCID: PMC6131669 DOI: 10.3389/fphys.2018.01228] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 08/14/2018] [Indexed: 12/21/2022] Open
Abstract
A nanodomain is a collection of proteins localized within a specialized, nanoscale structural environment, which can serve as the functional unit of macroscopic physiologic processes. We are beginning to recognize the key roles of cardiomyocyte nanodomains in essential processes of cardiac physiology such as electrical impulse propagation and excitation–contraction coupling (ECC). There is growing appreciation of nanodomain dysfunction, i.e., nanopathy, as a mechanistic driver of life-threatening arrhythmias in a variety of pathologies. Here, we offer an overview of current research on the role of nanodomains in cardiac physiology with particular emphasis on: (1) sodium channel-rich nanodomains within the intercalated disk that participate in cell-to-cell electrical coupling and (2) dyadic nanodomains located along transverse tubules that participate in ECC. The beat to beat function of cardiomyocytes involves three phases: the action potential, the calcium transient, and mechanical contraction/relaxation. In all these phases, cell-wide function results from the aggregation of the stochastic function of individual proteins. While it has long been known that proteins that exist in close proximity influence each other’s function, it is increasingly appreciated that there exist nanoscale structures that act as functional units of cardiac biophysical phenomena. Termed nanodomains, these structures are collections of proteins, localized within specialized nanoscale structural environments. The nano-environments enable the generation of localized electrical and/or chemical gradients, thereby conferring unique functional properties to these units. Thus, the function of a nanodomain is determined by its protein constituents as well as their local structural environment, adding an additional layer of complexity to cardiac biology and biophysics. However, with the emergence of experimental techniques that allow direct investigation of structure and function at the nanoscale, our understanding of cardiac physiology and pathophysiology at these scales is rapidly advancing. Here, we will discuss the structure and functions of multiple cardiomyocyte nanodomains, and novel strategies that target them for the treatment of cardiac arrhythmias.
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Affiliation(s)
- Przemysław B Radwański
- Bob and Corinne Frick Center for Heart Failure and Arrhythmia, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, United States.,Division of Pharmacy Practice and Science, College of Pharmacy, The Ohio State University, Columbus, OH, United States
| | - Christopher N Johnson
- Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Vanderbilt Center for Arrhythmia Research and Therapeutics, Nashville, TN, United States
| | - Sándor Györke
- Bob and Corinne Frick Center for Heart Failure and Arrhythmia, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, United States
| | - Rengasayee Veeraraghavan
- Bob and Corinne Frick Center for Heart Failure and Arrhythmia, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, United States.,Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States
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4
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Amoah BP, Yang H, Zhang P, Su Z, Xu H. Immunopathogenesis of Myocarditis: The Interplay Between Cardiac Fibroblast Cells, Dendritic Cells, Macrophages and CD4+T Cells. Scand J Immunol 2015; 82:1-9. [DOI: 10.1111/sji.12298] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2014] [Revised: 02/21/2015] [Accepted: 03/14/2015] [Indexed: 02/06/2023]
Affiliation(s)
- B. Prince Amoah
- Department of Immunology; School of Medical Science and Laboratory Medicine; Jiangsu University; Zhenjiang China
- Department of Biomedical and Forensic Sciences; School of Biological Sciences; University of Cape Coast; Cape Coast Ghana
| | - H. Yang
- Department of Immunology; School of Medical Science and Laboratory Medicine; Jiangsu University; Zhenjiang China
| | - P. Zhang
- Department of Immunology; School of Medical Science and Laboratory Medicine; Jiangsu University; Zhenjiang China
| | - Z. Su
- Department of Immunology; School of Medical Science and Laboratory Medicine; Jiangsu University; Zhenjiang China
- The Central Laboratory; The Fourth Affiliated Hospital of Jiangsu University; Zhenjiang China
| | - H. Xu
- Department of Immunology; School of Medical Science and Laboratory Medicine; Jiangsu University; Zhenjiang China
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5
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Dynamic changes in sarcoplasmic reticulum structure in ventricular myocytes. J Biomed Biotechnol 2011; 2011:382586. [PMID: 22131804 PMCID: PMC3206393 DOI: 10.1155/2011/382586] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 08/09/2011] [Indexed: 11/23/2022] Open
Abstract
The fidelity of excitation-contraction (EC) coupling in ventricular myocytes is remarkable, with each action potential evoking a [Ca2+]i transient. The prevalent model is that the consistency in EC coupling in ventricular myocytes is due to the formation of fixed, tight junctions between the
sarcoplasmic reticulum (SR) and the sarcolemma where Ca2+ release is activated. Here, we tested the hypothesis that the SR is a structurally inert organelle in ventricular myocytes. Our data suggest that rather than being static, the SR undergoes frequent dynamic structural changes. SR boutons expressing functional ryanodine receptors moved throughout the cell, approaching or moving away from the sarcolemma of ventricular myocytes. These changes in SR structure occurred in the absence of changes in [Ca2+]i during EC coupling. Microtubules and the molecular motors dynein and kinesin 1(Kif5b) were important regulators of SR motility. These findings support a model in which the SR is a motile organelle capable of molecular motor protein-driven structural changes.
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6
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Cannell MB, Kong CHT. Local control in cardiac E-C coupling. J Mol Cell Cardiol 2011; 52:298-303. [PMID: 21586292 DOI: 10.1016/j.yjmcc.2011.04.014] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 04/12/2011] [Accepted: 04/29/2011] [Indexed: 10/18/2022]
Abstract
The development of local control theories in cardiac excitation-contraction coupling solved a major problem in the calcium-induced calcium release (CICR) hypothesis. Local control explained how regeneration, inherent in the CICR mechanism, might be limited spatially to enable graded Ca release (and force production). The key lies in the stochastic recruitment of individual calcium release units (couplons or CRUs) where adjacent CRUs are partially uncoupled by the distance between them. In the CRU, individual groups of sarcoplasmic reticulum calcium release channels (RyRs) are very close to the surface membrane where calcium influx, controlled by membrane depolarization, leads to high local Ca levels that enable a high speed response from RyRs that have a very low probability to opening at resting Ca levels. However, calcium diffusion from an activated CRU results in adjacent CRUs being exposed to much lower levels of Ca and probability of activation. This effectively uncouples the CRUs and limits overall regenerative gain to enable stability without compromising sensitivity. Nevertheless, it is still unclear how the CRU terminates its release of calcium on the physiological timescale, and possible mechanisms (and problems) are briefly reviewed. We suggest that modulation in RyR gating may serve to control average SR Ca levels to regulate other metabolic functions of the sarco(endo)plasmic reticulum beyond regulating contractility. This article is part of a special issue entitled "Local Signaling in Myocytes."
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Affiliation(s)
- M B Cannell
- School of Physiology & Pharmacology, University of Bristol, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK.
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7
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Borg TK, Baudino TA. Dynamic interactions between the cellular components of the heart and the extracellular matrix. Pflugers Arch 2011; 462:69-74. [PMID: 21399896 DOI: 10.1007/s00424-011-0940-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Revised: 02/10/2011] [Accepted: 02/11/2011] [Indexed: 01/08/2023]
Abstract
The heart is composed of both cellular and acellular components that act in a dynamic fashion from birth to death. The cellular components consist of myocytes, fibroblasts, and vascular cells, including endothelium and smooth muscle. Changes in these components are intimately associated with function by altering the mechanical, chemical, and electrical properties of the heart. In future investigations, it will be important to examine these interactions as dynamic changes in response to physiological signals.
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Affiliation(s)
- Thomas K Borg
- Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA.
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8
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Müller O, Tian Q, Zantl R, Kahl V, Lipp P, Kaestner L. A system for optical high resolution screening of electrical excitable cells. Cell Calcium 2010; 47:224-33. [DOI: 10.1016/j.ceca.2009.11.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2009] [Revised: 10/15/2009] [Accepted: 11/27/2009] [Indexed: 11/28/2022]
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9
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Scriven DRL, Klimek A, Asghari P, Bellve K, Moore EDW. Caveolin-3 is adjacent to a group of extradyadic ryanodine receptors. Biophys J 2005; 89:1893-901. [PMID: 15980179 PMCID: PMC1366692 DOI: 10.1529/biophysj.105.064212] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Caveolae are present in almost all cells and concentrate a wide variety of signaling molecules, receptors, transporters, and ion pumps. We have investigated the distribution of the ryanodine receptor, the Na(+)/Ca(2+) exchanger, the predominant Na(+) channel isoform rH1, and the L-type calcium channel, Ca(v)1.2, relative to the muscle-specific caveolin isoform, caveolin-3, in adult rat ventricular myocytes. Three-dimensional immunofluorescence images were deconvolved and analyzed. Caveolin-3 colocalizes with all of these molecules at the surface of the cell, but there is no significant colocalization between caveolin-3 and either the Na(+)/Ca(2+) exchanger or the Na(+) channel in the cell interior. The distribution of the surface colocalization indicates that the caveolae that colocalize with each molecule form distinct populations. This organization indicates that there are multiple populations of caveolae separable by location and occupants. In the interior of the cell, caveolin-3 shows a marked colocalization with a population of ryanodine receptors that are separate from those within the dyad. Because of their location, the signaling molecules contained within these caveolae may have preferred access to the neighboring nondyadic ryanodine receptors.
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Affiliation(s)
- David R L Scriven
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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10
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Abstract
Cardiac muscle has been extensively studied, but little information is available on the detailed macromolecular structure of its thick filament. To elucidate the structure of these filaments I have developed a procedure to isolate the cardiac thick filaments for study by electron microscopy and computer image analysis. This procedure uses chemical skinning with Triton X-100 to avoid contraction of the muscle that occurs using the procedures previously developed for isolation of skeletal muscle thick filaments. The negatively stained isolated filaments appear highly periodic, with a helical repeat every third cross-bridge level (43 nm). Computed Fourier transforms of the filaments show a strong set of layer lines corresponding to a 43-nm near-helical repeat out to the 6th layer line. Additional meridional reflections extend to at least the 12th layer line in averaged transforms of the filaments. The highly periodic structure of the filaments clearly suggests that the weakness of the layer lines in x-ray diffraction patterns of heart muscle is not due to an inherently more disordered cross-bridge arrangement. In addition, the isolated thick filaments are unusual in their strong tendency to remain bound to actin by anti-rigor oriented cross-bridges (state II or state III cross-bridges) under relaxing conditions.
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Affiliation(s)
- Robert W Kensler
- Department of Anatomy, University of Puerto Rico Medical School, Medical Sciences Campus, San Juan, Puerto Rico 00936-5067, USA.
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11
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Parker KK, Taylor LK, Atkinson JB, Hansen DE, Wikswo JP, Atkinson B. The effects of tubulin-binding agents on stretch-induced ventricular arrhythmias. Eur J Pharmacol 2001; 417:131-40. [PMID: 11301068 DOI: 10.1016/s0014-2999(01)00856-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Stretch-activated ion channels have been identified as transducers of mechanoelectric coupling in the heart, where they may play a role in arrhythmogenesis. The role of the cytoskeleton in ion channel control has been a topic of recent study and the transmission of mechanical stresses to stretch-activated channels by cytoskeletal attachment has been hypothesized. We studied the arrhythmogenic effects of stretch in 16 Langendorff-perfused rabbit hearts in which we pharmacologically manipulated the microtubular network of the cardiac myocytes. Group 1 (n=5) was treated with colchicine, which depolymerizes microtubules, and Group 2 (n=6) was treated with taxol, which polymerizes microtubules. Stretch-induced arrhythmias were produced by transiently increasing the volume of a fluid-filled left ventricular balloon with a volume pump driven by a computer-controlled stepper motor. Electrical events were recorded by a contact electrode which provided high-fidelity recordings of monophasic action potentials and stretch-induced depolarizations. The probability of eliciting a stretch-induced arrhythmia increased (0.22+/-0.11 to 0.62+/-0.19, p=0.001) in hearts treated with taxol (5 microM), whereas hearts treated with colchicine (100 microM) showed no statistically significant change. We conclude that proliferation of microtubules increased the arrhythmogenic effect of transient left ventricle diastolic stretch. This result indicates a possible mode of arrhythmogenesis in chemotherapeutic patients and patients exhibiting uncompensated ventricular hypertrophy. The data would indicate that the cytoskeleton represents a possible target for antiarrhythmic therapies.
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Affiliation(s)
- K K Parker
- Living State Physics Group, Department of Physics and Astronomy, Vanderbilt University, Box 1807 Station B, Nashville, TN 37235, USA
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12
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Simpson DG, Carver W, Borg TK, Terracio L. Role of mechanical stimulation in the establishment and maintenance of muscle cell differentiation. INTERNATIONAL REVIEW OF CYTOLOGY 1994; 150:69-94. [PMID: 8169083 DOI: 10.1016/s0074-7696(08)61537-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- D G Simpson
- Department of Developmental Biology and Anatomy, School of Medicine, University of South Carolina, Columbia 29208
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13
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Ioshii SO, Imanaka-Yoshida K, Yoshida T. Organization of calsequestrin-positive sarcoplasmic reticulum in rat cardiomyocytes in culture. J Cell Physiol 1994; 158:87-96. [PMID: 8263032 DOI: 10.1002/jcp.1041580112] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The sarcoplasmic reticulum (SR) regulates the levels of cytoplasmic free Ca2+ ions in muscle cells. Calsequestrin is a major Ca(2+)-storing protein and is localized at special sites in the SR. To investigate the development of calsequestrin-positive SR and its interaction with the cytoskeleton, we examined the distribution of calsequestrin in cultured cardiomyocytes from newborn rats by immunofluorescence with anticalsequestrin and antitubulin antibodies and rhodamine-phalloidin. In frozen sections of neonatal rat heart, anticalsequestrin immunostaining was apparent as cross-striations at Z-lines. When newborn cardiomyocytes were isolated, calsequestrin-positive SR was disorganized and was apparent as small vesicles beneath the sarcolemma, whereas myofibrils accumulated in the center of the cells. As the cells spread in culture, calsequestrin-positive vesicles spread to the periphery of the cytoplasm, becoming associated with the developing myofibrils. In mature cells, calsequestrin was closely associated with myofibrils, showing cross-striations at the Z-lines. Double-labeling using anticalsequestrin and antitubulin antibodies demonstrated that the distribution of calsequestrin-positive structures was similar to that of the microtubular arrays. When the microtubules were depolymerized by nocodazole at an early stage, the extension of the SR to the cell periphery was inhibited. In mature cardiomyocytes, nocodazole appeared not to affect the distribution of the SR. These results indicate that the calsequestrin-positive SR in cardiomyocytes is organized at the proper sites of myofibrils during myofibrillogenesis and that the microtubules might serve as tracts for the transport of components of the SR.
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Affiliation(s)
- S O Ioshii
- Department of Pathology, Mie University School of Medicine, Japan
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14
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Jorgensen AO, Shen AC, Arnold W, McPherson PS, Campbell KP. The Ca2+-release channel/ryanodine receptor is localized in junctional and corbular sarcoplasmic reticulum in cardiac muscle. J Cell Biol 1993; 120:969-80. [PMID: 8381786 PMCID: PMC2200068 DOI: 10.1083/jcb.120.4.969] [Citation(s) in RCA: 112] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The subcellular distribution of the Ca(2+)-release channel/ryanodine receptor in adult rat papillary myofibers has been determined by immunofluorescence and immunoelectron microscopical studies using affinity purified antibodies against the ryanodine receptor. The receptor is confined to the sarcoplasmic reticulum (SR) where it is localized to interior and peripheral junctional SR and the corbular SR, but it is absent from the network SR where the SR-Ca(2+)-ATPase and phospholamban are densely distributed. Immunofluorescence labeling of sheep Purkinje fibers show that the ryanodine receptor is confined to discrete foci while the SR-Ca(2+)-ATPase is distributed in a continuous network-like structure present at the periphery as well as throughout interior regions of these myofibers. Because Purkinje fibers lack T-tubules, these results indicate that the ryanodine receptor is localized not only to the peripheral junctional SR but also to corbular SR densely distributed in interfibrillar spaces of the I-band regions. We have previously identified both corbular SR and junctional SR in cardiac muscle as potential Ca(2+)-storage/Ca(2+)-release sites by demonstrating that the Ca2+ binding protein calsequestrin and calcium are very densely distributed in these two specialized domains of cardiac SR in situ. The results presented here provide strong evidence in support of the hypothesis that corbular SR is indeed a site of Ca(2+)-induced Ca2+ release via the ryanodine receptor during excitation contraction coupling in cardiac muscle. Furthermore, these results indicate that the function of the cardiac Ca(2+)-release channel/ryanodine receptor is not confined to junctional complexes between SR and the sarcolemma.
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Affiliation(s)
- A O Jorgensen
- Department of Anatomy and Cell Biology, University of Toronto, Ontario, Canada
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15
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Dalen H, Lieberman M, LeFurgey A, Scheie P, Sommer JR. Quick-freezing of cultured cardiac cells in situ with special attention to the mitochondrial ultrastructure. J Microsc 1992; 168:259-73. [PMID: 1484378 DOI: 10.1111/j.1365-2818.1992.tb03268.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A new method has been developed which allows quick-freezing in situ of primary, cardiac cell cultures grown to confluence on gas-permeable membranes (Petriperm dishes). Small pieces of the growth substratum, with rhythmically beating myocardial cells, were slam-frozen, without cryoprotectants, against the surface of a helium-cooled copper block at approximately 16 K. The quality of the cellular cryopreservation, as judged by ultrastructural criteria, was studied in freeze-substituted specimens processed for transmission electron microscopy. The ultrastructure of cryofixed cardiac cells was compared with that of unfrozen, chemically fixed samples. The severity of cryodistortions increased progressively with increasing distance from the point of first impact. Of particular interest were the dramatic alterations of the mitochondrial ultrastructure. The concept that the reticular and the outer mitochondrial membranes are intimately and strongly associated was clearly demonstrated. Optimally frozen material revealed cryopreserved ultrastructure of high quality. The method described appears to offer an ideal model system for correlating the information gained by phase-contrast microscopy of living cell cultures with the ultrastructure of the same samples fixed in situ by chemical or physical techniques. Cryofixation would be particularly useful for studying dynamic cellular processes associated with physiological and pathophysiological conditions, e.g. metabolic inhibition, anoxia and substrate deprivation.
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Affiliation(s)
- H Dalen
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710
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16
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Forbes MS, Mock OB, Van Niel EE. Ultrastructure of the myocardium of the least shrew, Cryptotis parva Say. Anat Rec (Hoboken) 1990; 226:57-70. [PMID: 2297084 DOI: 10.1002/ar.1092260108] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The heart of the least shrew, Cryptotis parva Say, is an extremely active organ, capable of achieving rates of 800-1,200 beats/minute. The general features of myocardial cell ultrastructure in this insectivore are much like those of other small mammals; no single striking feature of fine structure is present to which the physiological properties of this heart might necessarily be attributed. Still there exist in these myocardial cells a number of atypical properties. These include 1) mitochondria having a wide variety of sizes and internal configurations 2) a pleiomorphic, highly ramified, small-diameter transverse-axial tubular system (TATS) 3) numerous "labyrinths," which are proliferated components of the TATS, and 4) myofibril-free regions, located both in juxtanuclear and other myoplasmic levels and populated by a concentration of TATS elements and fibrillar structures. Features (2) and (3) are also characteristic of another fast-beating heart, that of the mouse. The sinoatrial and atrioventricular nodal regions, as well as a Purkinje system, have been identified in the least shrew heart, along with sparsely distributed atrial cells whose myofibrils contain proliferated Z-band material. A feature frequently encountered in atrial working muscle cells is the occurrence of close appositions between gap junctions and tubules of sarcoplasmic reticulum; such appositions are also present in other regions of the shrew heart, as are complexes composed of gap junctions and mitochondria.
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Affiliation(s)
- M S Forbes
- Department of Physiology, University of Virginia School of Medicine, Charlottesville 22908
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17
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Dalen H. An ultrastructural study of the hypertrophied human papillary muscle cell with special emphasis on specific staining patterns, mitochondrial projections and association between mitochondria and SR. VIRCHOWS ARCHIV. A, PATHOLOGICAL ANATOMY AND HISTOPATHOLOGY 1989; 414:187-98. [PMID: 2467430 DOI: 10.1007/bf00822022] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Biopsy material of the hypertrophied human papillary muscle has been processed according to various electron microscopical techniques in order to study the mitochondrial ultrastructure and the association between mitochondria and sarcoplasmic reticulum (SR). En bloc staining with a Cu-Pb citrate solution resulted in specifically contrasted mitochondrial and sarcotubular membranes, characterized by numerous, discrete, electron-dense particles. The differences in staining patterns between the perinuclear mitochondria and their subsarcolemmal and interfibrillar counterparts suggest differences in chemical properties and/or metabolic activities. The selectively contrasted mitochondrial particles may represent a conglomerate of extrinsic and intrinsic respiratory enzymes and other membrane-associated proteins, while the majority of the electron-dense particles of the sarcotubular membrane may represent positively stained Ca2+-pumps. Ultrastructural findings in the present study strongly indicate that the slender mitochondrial projections represent an initial stage in a process leading to the formation of large and pleomorphic mitochondria. Intimate contact between adjacent mitochondria as well as between mitochondria and SR are documented. In the contact regions some of the specifically contrasted particles of the adjacent membranes had fused with each other. It is suggested that these particles represent membrane-bound transport proteins providing a system for inter-organelle exchange of metabolites and/or ions.
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Affiliation(s)
- H Dalen
- Laboratory of Clinical Electron Microscopy, University of Bergen, Haukeland Hospital, Norway
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Jorgensen AO, Broderick R, Somlyo AP, Somlyo AV. Two structurally distinct calcium storage sites in rat cardiac sarcoplasmic reticulum: an electron microprobe analysis study. Circ Res 1988; 63:1060-9. [PMID: 3058361 DOI: 10.1161/01.res.63.6.1060] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The elemental composition of subcellular organelles in resting rat papillary muscle was measured by electron probe x-ray microanalysis of cryosections of flash-frozen tissue. Nonmitochondrial electron-dense structures (50-100 nm in diameter) with a phosphorous concentration larger than 375 mmol/kg dry wt were identified in the interfibrillar spaces of the I band region. They were not visible in the proximity of transverse tubules. The sodium, magnesium, phosphorus, sulfur, chlorine, and potassium content of the electron dense structures showed a normal distribution, consistent with a uniform composition of a specific subcellular organelle. However, the distribution of the calcium concentrations in these electron-dense structures was bimodal, suggesting that they are composed of at least two subpopulations. One subpopulation had relatively high calcium (up to 53 mmol/kg dry wt) content with a mean value of 12.5 +/- 1.1 mmol/kg dry wt, while the other one had a relatively low calcium content with a mean value of 2.8 +/- 0.3 mmol/kg dry wt. The mean calcium concentration in the junctional sarcoplasmic reticulum (j-SR) in rat papillary muscle with calcium concentrations larger than 6 mmol/kg dry wt was 14.6 +/- 2.0 mmol/kg dry wt. We propose that the electron-dense structures described above correspond to nonjunctional sarcoplasmic reticulum and that the population containing relatively high calcium concentrations is calsequestrin-containing corbular sarcoplasmic reticulum (c-SR) confined to the I band region, while the population containing relatively low calcium concentrations corresponds to anastomosing regions of the network sarcoplasmic reticulum that lack calsequestrin.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- A O Jorgensen
- Department of Anatomy, Faculty of Medicine, University of Toronto, Canada
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Rappaport L, Samuel JL. Microtubules in cardiac myocytes. INTERNATIONAL REVIEW OF CYTOLOGY 1988; 113:101-43. [PMID: 2976409 DOI: 10.1016/s0074-7696(08)60847-5] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- L Rappaport
- INSERM U 127, Hôpital Lariboisière, Paris, France
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Tomita Y, Ferrans VJ. Morphological study of sarcoplasmic reticulum in the atrioventricular node and bundle cells in guinea pig hearts. THE AMERICAN JOURNAL OF ANATOMY 1987; 180:100-22. [PMID: 3661462 DOI: 10.1002/aja.1001800108] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The osmium-ferrocyanide method for staining of the sarcoplasmic reticulum (SR) was used for a morphological investigation of the various components of the SR in the atrioventricular node and bundle (AVNB) cells of guinea pig hearts. On the basis of light microscopic observations, the AVNB tissue in guinea pig hearts can be divided into five regions: atrionodal junction, midnode, proximal bundle, distal bundle, and bundle branches. Electron microscopic observations revealed two types of junctional SR (j-SR) saccules in the cells from all the regions of AVNB tissue. One is similar to that seen in the working cardiac cells, i.e., flattened saccules with junctional granules. The second type is dilated and contains electron-dense granular material throughout its lumen. The flattened type is seen more often than the dilated type in atrionodal junctional cells and midnode cells, whereas the dilated type occurs more often in distal bundle cells and bundle branch cells. In most cells from the atrionodal junction and midnode regions, the j-SR saccules are apposed more often to sarcolemmal areas associated with nonspecialized regions of intercellular junctions than to other sarcolemmal areas. This distribution was not found in the distal bundle and bundle branch cells. Free SR tubules around the myofilament bundles are poorly developed in the midnode cells, generally in accord with the extent of development of myofibrils. Z-tubules are found in cells from all regions but are poorly developed in midnode cells. Corbular SR vesicles are found in cells from all the regions of AVNB tissues but are rare in midnode cells. Thus, each of the regions in the AVNB tissue has a different, characteristic distribution of SR components. Because of their possible relationship to the regulation of the intracellular concentrations of calcium, these differences in SR morphology may contribute to the diverse physiological properties of the different regions of the AV node and bundle.
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Affiliation(s)
- Y Tomita
- Surgery Branch, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892
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Jorgensen AO, Jones LR. Immunoelectron microscopical localization of phospholamban in adult canine ventricular muscle. J Biophys Biochem Cytol 1987; 104:1343-52. [PMID: 3553210 PMCID: PMC2114482 DOI: 10.1083/jcb.104.5.1343] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The subcellular distribution of phospholamban in adult canine ventricular myocardial cells was determined by the indirect immunogold-labeling technique. The results presented suggest that phospholamban, like the Ca2+-ATPase, is uniformly distributed in the network sarcoplasmic reticulum but absent from the junctional portion of the junctional sarcoplasmic reticulum. Unlike the Ca2+-ATPase, but like cardiac calsequestrin, phospholamban also appears to be present in the corbular sarcoplasmic reticulum. Comparison of the relative distribution of phospholamban immunolabeling in the sarcoplasmic reticulum with that of the sarcolemma showed that the density of phospholamban in the network sarcoplasmic reticulum was approximately 35-fold higher than that of the cytoplasmic side of the sarcolemma, which in turn was found to be three- to fourfold higher than the density of the background labeling. However, a majority of the specific phospholamban labeling within 30 nm of the cytoplasmic side of the sarcolemma was clustered and present over the sarcoplasmic reticulum in the subsarcolemmal region of the myocardial cells, suggesting that phospholamban is confined to the junctional regions between the sarcolemma and the sarcoplasmic reticulum, but absent from the nonjunctional portion of the sarcolemma. Although the resolution of the immunogold-labeling technique used (60 nm) does not permit one to determine whether the specific labeling within 30 nm of the cytoplasmic side of the sarcolemma is associated with the sarcolemma and/or the junctional sarcoplasmic reticulum, it is likely that the low amount of labeling in this region represents phospholamban associated with sarcoplasmic reticulum. These results suggest that phospholamban is absent from the sarcolemma and confined to the sarcoplasmic reticulum in cardiac muscle.
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Watkins SC, Samuel JL, Marotte F, Bertier-Savalle B, Rappaport L. Microtubules and desmin filaments during onset of heart hypertrophy in rat: a double immunoelectron microscope study. Circ Res 1987; 60:327-36. [PMID: 2953507 DOI: 10.1161/01.res.60.3.327] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The distribution of tubulin and desmin, the constituent proteins of microtubules and intermediate filaments, respectively, were studied in normal and hypertrophied rat myocardium by high-resolution immunofluorescence and immunoelectron microscopy. Cardiac hypertrophy was induced in 25-day-old rats by aortic stenosis. In the normal heart, double immunolabelling of ultrathin frozen sections of papillary muscle using gold-labelled probes for tubulin and desmin showed that microtubules ran primarily in a longitudinal direction through the intermyofibrillar spaces, perpendicularly to the desmin filaments. Microtubules were present near nuclei, mitochondria, and plasma membranes, while desmin filaments formed transverse connections between adjacent Z disks. No tubulin was observed near the intercalated disks, which were rich in desmin filaments. In hypertrophied hearts, myocytes exhibited the typical morphological features of developing hypertrophy. While there was little difference in the distribution of the microtubules around mitochondria and at the plasma membrane, considerable increases were seen near the nuclei and along the myofibrils. Desmin labelling was distributed transversely as in the controls; however, sometimes it was longitudinally oriented either in the intermyofibrillar space linking 2 Z disks out of register or along digitations of the intercalated disks connecting neighboring desmosomes. The unique rearrangement of desmin and tubulin filaments in hypertrophied cardiac myocytes emphasizes their distinct role in myocyte organization. We suggest that, during the development of cardiac hypertrophy, desmin filaments are mainly involved in maintaining the myofibrils in register, whereas the degree of assembly of microtubules is correlated with the rate of protein synthesis and with myofibrillogenesis.
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Dalen H, Saetersdal T, Odegården S. Some ultrastructural features of the myocardial cells in the hypertrophied human papillary muscle. VIRCHOWS ARCHIV. A, PATHOLOGICAL ANATOMY AND HISTOPATHOLOGY 1987; 410:281-94. [PMID: 2949420 DOI: 10.1007/bf00711285] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
An ultrastructural study using various electron microscopical techniques has been conducted on biopsy material from the hypertrophied papillary muscle of the human heart. About 75% of the myocardial cells were classified as hypertrophic with diameters ranging from 15 micron to 53 micron. The increased cell diameter appeared to be the result of an elevated amount of mitochondria and contractile material. The hypertrophied myocytes displayed a general ultrastructural organization in many ways similar to that of the normal sized myocytes. However, the former cells were characterized by focal deposits of excess laminar coat material and abnormal Z-band patterns as well as of multiple intercalated discs. The preferential sites for the production of new sarcomere elements appeared to be in the subsarcolemmal and intercalated disc regions. Adjacent myocardial cells were interconnected by collagen bundles, and, by an elaborate collagen-fibril-microthread-granule lattice. The surface folds were linked to each other by surface cables, which probably constituted a separate category of extracellular material of unknown function. Intramembranous particles were abundant in the sarcolemma proper but scarce in the membranes of the sarcoplasmic vesicles. Such particles were also observed in the lipofuscin granular membrane and in the membranes surrounding the lipid droplets. A framework of transverse cytoskeletal filaments interconnected the Z-bands of adjacent myofibrils and anchored the contractile material to the sarcolemma as well as to the nucleus. A large and lobulated nucleus containing well developed nucleoli together with an abundance of sarcoplasmic free and membrane-attached ribosomes, were interpreted as morphological signs of enhanced synthetic activity in the hypertrophied cell. Degenerative phenomena on the other hand were confined to lysosomal degeneration of worn-out cell constituents that were manifested by the numerous lysosomes and aggregates of lipofuscin granules. Abnormal Z-band patterns as seen in the present material were interpreted as an initial stage in the formation of new contractile elements.
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Dalen H, Odegården S, Saetersdal T. The application of various electron microscopic techniques for ultrastructural characterization of the human papillary heart muscle cell in biopsy material. VIRCHOWS ARCHIV. A, PATHOLOGICAL ANATOMY AND HISTOPATHOLOGY 1987; 410:265-79. [PMID: 3101279 DOI: 10.1007/bf00711284] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Various electron microscopical techniques have been applied to biopsy material obtained from patients suffering from mitral stenosis in order to characterize the subcellular organization of the hypertrophied papillary muscle. Small pieces of the same sample were processed for correlative transmission - (TEM) and scanning - (SEM) electron microscopical studies. TEM was carried out on conventionally fixed tissue with or without en bloc staining with a Cu-Pb citrate solution, and on freeze fracture replicas, while cryofractured material was studied by SEM. Stereo electron micrographs of the Cu-Pb impregnated tissue and of the cryofractured material were especially useful for studying the spatial distribution and relationship between various cell organelles. The myofilaments of the hypertrophied cells were arranged in a normal hexagonal pattern. Regions with irregular orientation of the myofibrils were occasionally seen. Accumulations of interfilamentous glycogen particles adjacent to the Z-bands were characteristic patterns of the contracted muscle cells. The extensive nexuses frequently observed in the subsarcolemmal regions may reflect functional alterations of the intercommunication between hypertrophied cells. The T-tubules were relatively few and irregularly distributed, and the complexity of the sarcotubular system (SR) revealed regional variations. Excellent visualization of the interior couplings between the SR and the T-tubules was achieved by studying thick sections of Cu-Pb impregnated tissue in the TEM. The dense staining of the various intracellular membranes when compared with the almost unstained external membranes including the free cell surface, intercalated disc and T-system, strongly indicates differences in chemical and functional properties of the two membrane systems. En bloc staining resulted also in contrasted glycogen as well as components of the nucleolus and the heterochromatin. The biochemical basis for the selective staining remains obscure; it may be a result of binding of heavy metal ions to carboxyl groups of specific proteins, and/or it may represent deposits of lead phosphate.
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Larsen TH, Saetersdal T, Grong K. The ultrastructure of the myocyte in different regions of experimental infarcts in the cat heart. RESEARCH IN EXPERIMENTAL MEDICINE. ZEITSCHRIFT FUR DIE GESAMTE EXPERIMENTELLE MEDIZIN EINSCHLIESSLICH EXPERIMENTELLER CHIRURGIE 1986; 186:295-306. [PMID: 3764092 DOI: 10.1007/bf01852306] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The ultrastructure of myocytes was studied in the left ventricular myocardium of the cat heart after 3 h of LAD ligation. The ischemic, borderline, and normally perfused myocardium was defined by in vivo injection of fluorescein and by regional myocardial blood flow measurements with 15.5 microns radio-labeled microspheres. A semiquantitation of the number of irreversible injured cells in per cent of total counted in the three different zones showed that 53%-63% were irreversibly injured in the ischemic zone, 7%-26% in the borderline area, while none were irreversibly injured in the normally perfused myocardium. The interior excitation-contraction couplings in the normally perfused myocardium comprise interior dyads, triads, reversed triads, and encircling couplings. While the couplings in general were structurally resistant to ischemia, injured interior couplings were apparent in severely damaged cells of the hypoperfused tissue. Such injuries comprise a widening of the junctional gap and a disintegration of the junctional processes.
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Steenbergen C, Hill ML, Jennings RB. Volume regulation and plasma membrane injury in aerobic, anaerobic, and ischemic myocardium in vitro. Effects of osmotic cell swelling on plasma membrane integrity. Circ Res 1985; 57:864-75. [PMID: 4064260 DOI: 10.1161/01.res.57.6.864] [Citation(s) in RCA: 124] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The relationship between cell swelling and plasma membrane disruption has been evaluated in thin myocardial slices incubated in oxygenated or anoxic Krebs-Ringer phosphate media. Electron microscopy and measurements of inulin-diffusible space were used to monitor plasma membrane integrity. Inulin is excluded from the intracellular space of intact cells; therefore, an increase in tissue inulin content is an excellent marker of loss of plasma membrane integrity. Cell volume was increased during exposure of aerobic slices to hypotonic media, but the inulin-diffusible space was not increased and electron micrographs showed no detectable plasma membrane alterations. Likewise, during prolonged anoxic isotonic incubation, no evidence of plasma membrane damage was observed. Incubation in anoxic hypotonic media for 60 minutes resulted in a larger increase in cell volume than under aerobic conditions, but plasma membrane integrity was maintained. Extended anoxic hypotonic incubation (300 minutes) produced no further change in tissue water, but the inulin-diffusible space was increased and electron micrographs revealed breaks in the plasma membranes primarily in association with large subsarcolemmal blebs. Likewise, myocardial slices incubated in isotonic anoxic media for 240 minutes and hypotonic anoxic media for 60 minutes had an increased inulin-diffusible space and the ultrastructural appearance was similar. This ultrastructural appearance is indistinguishable from that observed in myocytes lethally injured by ischemia. Measurements of tissue osmolarity during total ischemia showed that osmotically induced cell swelling could occur in ischemic myocardium prior to the onset of plasma membrane disruption. Our results indicate that cell swelling per se is incapable of rupturing plasma membranes; however, after prolonged periods of energy deficiency, the plasma membrane or its cytoskeletal scaffold become injured, which allows the membrane to rupture if the cell is swollen, as might occur during ischemia or reperfusion.
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Jorgensen AO, Shen AC, Campbell KP. Ultrastructural localization of calsequestrin in adult rat atrial and ventricular muscle cells. J Cell Biol 1985; 101:257-68. [PMID: 4008530 PMCID: PMC2113628 DOI: 10.1083/jcb.101.1.257] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The distribution of calsequestrin in rat atrial and ventricular myocardial cells was determined by indirect immunocolloidal gold labeling of ultrathin frozen sections. The results presented show that calsequestrin is confined to the sarcoplasmic reticulum where it is localized in the lumen of the peripheral and the interior junctional sarcoplasmic reticulum as well as in the lumen of the corbular sarcoplasmic reticulum, but absent from the lumen of the network sarcoplasmic reticulum. Comparison of these results with our previous studies on the distribution of the Ca2+ + Mg2+-dependent ATPase of the cardiac sarcoplasmic reticulum show directly that the Ca2+ + Mg2+-dependent ATPase and calsequestrin are confined to distinct regions within the continuous sarcoplasmic reticulum membrane. Assuming that calsequestrin provides the major site of Ca2+ sequestration in the lumen of the sarcoplasmic reticulum, the results presented support the idea that both junctional (interior and peripheral) and specialized nonjunctional (corbular) regions of the sarcoplasmic reticulum are involved in Ca2+ storage and possibly release. Furthermore, the structural differences between the junctional and the corbular sarcoplasmic reticulum support the possibility that Ca2+ storage and/or release from the lumen of the junctional and the corbular sarcoplasmic reticulum are regulated by different physiological signals.
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Jorgensen AO, McLeod AG, Campbell KP, Denney GH. Evidence for the presence of calsequestrin in both peripheral and interior regions of sheep Purkinje fibers. Circ Res 1984; 55:267-70. [PMID: 6378421 DOI: 10.1161/01.res.55.2.267] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Localization of calsequestrin in sheep Purkinje fibers was determined by indirect immunofluorescence labeling of cryostat sections of sheep myocardium from the intraventricular wall. The results presented show that calsequestrin is present in discrete foci at the peripheral, as well as the interior regions of the cytoplasm. Since Purkinje fibers lack transverse tubules, the presence of calsequestrin at specific foci in the interior regions of the cytoplasm in these cells suggests that calsequestrin is localized in the lumen of peripheral junctional sarcoplasmic reticulum, as well as in the lumen of corbular sarcoplasmic reticulum present in the I band region of the myofibrils. Assuming that the function of calsequestrin is to sequester calcium into the lumen of the sarcoplasmic reticulum, these results imply that two structurally different regions of the sarcoplasmic reticulum function as calcium storage sites in mammalian Purkinje fibers and raises the possibility that calcium storage and/or release from these two sites might be regulated differently.
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Forbes MS, Hawkey LA, Sperelakis N. The transverse-axial tubular system (TATS) of mouse myocardium: its morphology in the developing and adult animal. THE AMERICAN JOURNAL OF ANATOMY 1984; 170:143-62. [PMID: 6465048 DOI: 10.1002/aja.1001700203] [Citation(s) in RCA: 72] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Invaginations of the sarcolemma that generate the transverse-axial tubular system (TATS) of the ventricular myocardial cells have begun to develop in the mouse by the time of birth. The formation of the TATS appears to be derived from the repetitive generation of caveolae, which forms "beaded tubules". Beaded tubules are retained in the adult, in which they frequently present a spiraled topography. Development of the TATS progresses so rapidly that complex systems are already present in the cardiac muscle cells of young mice; by 10-14 days of age, the ultrastructure is essentially identical to that of the adult. The mouse myocardial TATS is composed of anastomosed elements that are directed transversely and axially (longitudinally). Many tubules have an oblique orientation, however, and most elements of the TATS are highly pleiomorphic. In this respect the TATS of the mouse heart is relatively primitive in appearance in comparison with the more ordered TATS latticeworks typical of the ventricular cells of other mammals. Stereological analysis of the mouse TATS indicates that the volume fraction (VV) and surface density (SV) are considerably greater than previously reported (3.24% and 0.5028 micron-1, respectively). The most complex ramifications of the TATS are embodied in the subsarcolemmal caveolar system and the deeper tubulovesicular "labyrinths", both of which can be found in early postnatal and adult ventricular cells. In atrial cells, TATS development is initiated several days later than in the ventricular cells. The TATS of adult atrial myocardial cells is less prominent than the ventricular TATS and consists largely of axial elements; the incidence of the TATS, furthermore, is more pronounced in the left than in the right atrium.
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Jorgensen AO, Campbell KP. Evidence for the presence of calsequestrin in two structurally different regions of myocardial sarcoplasmic reticulum. J Cell Biol 1984; 98:1597-602. [PMID: 6371026 PMCID: PMC2113214 DOI: 10.1083/jcb.98.4.1597] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Localization of calsequestrin in chicken ventricular muscle cells was determined by indirect immunofluorescence and immuno-Protein A-colloidal gold labeling of cryostat and ultracryotomy sections, respectively. Calsequestrin was localized in the lumen of peripheral junctional sarcoplasmic reticulum, as well as in the lumen of membrane-bound structures present in the central region of the I-band, while being absent from the lumen of the sarcoplasmic reticulum in the A-band region of the cardiac muscle cells. Since chicken ventricular muscle cells lack transverse tubules, the presence of calsequestrin in membrane bound structures in the central region of the I-band suggests that these cells contain nonjunctional regions of sarcoplasmic reticulum that are involved in Ca2+ storage and possibly Ca2+ release. It is likely that the calsequestrin containing structures present throughout the I-band region of the muscle cells correspond to specialized regions of the free sarcoplasmic reticulum in the I-band called corbular sarcoplasmic reticulum. It will be of interest to determine whether Ca2+ storage and possibly Ca2+ release from junctional and nonjunctional regions of the sarcoplasmic reticulum in chicken ventricular muscle cells are regulated by the same or different physiological signals.
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Abstract
Cytoplasmic microtubules can be divided into two subpopulations: 1) those adjacent to the nucleus (perinuclear), and 2) those distributed between the myofilament bundles (nonperinuclear). Previous observations (Cartwright and Goldstein, '83) indicate total cytoplasmic microtubule numeric density increases to a maximum at 5-9 days and decreases to the steady value of the adult muscle. We have examined the numeric density (mean numbers of microtubule profiles per micron2 cross-sectional area) of the perinuclear subpopulation and compared it to the numeric density of the total cytoplasmic microtubule population in postnatally developing rat papillary muscle ages 1, 3, 5, 9, 21, and 42 days, and adult. The perinuclear region was defined as the area around the nucleus which extends to the 0.273 micron from the nuclear envelope. The density of perinuclear microtubules did not change with postnatal development. Our study suggests that perinuclear microtubules are a separate and relatively stable subpopulation of the total population of cytoplasmic microtubules and may serve a function different from that of the more variable nonperinuclear microtubules.
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Forbes MS, Sperelakis N. Ultrastructure of Mammalian Cardiac Muscle. PHYSIOLOGY AND PATHOPHYSIOLOGY OF THE HEART 1984. [DOI: 10.1007/978-1-4757-1171-4_1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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