1
|
A fundamental evaluation of the electrical properties and function of cardiac transverse tubules. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2019; 1867:118502. [PMID: 31269418 DOI: 10.1016/j.bbamcr.2019.06.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 06/07/2019] [Accepted: 06/28/2019] [Indexed: 11/20/2022]
Abstract
This work discusses active and passive electrical properties of transverse (T-)tubules in ventricular cardiomyocytes to understand the physiological roles of T-tubules. T-tubules are invaginations of the lateral membrane that provide a large surface for calcium-handling proteins to facilitate sarcomere shortening. Higher heart rates correlate with higher T-tubular densities in mammalian ventricular cardiomyocytes. We assess ion dynamics in T-tubules and the effects of sodium current in T-tubules on the extracellular potential, which leads to a partial reduction of the sodium current in deep segments of a T-tubule. We moreover reflect on the impact of T-tubules on macroscopic conduction velocity, integrating fundamental principles of action potential propagation and conduction. We also theoretically assess how the conduction velocity is affected by different T-tubular sodium current densities. Lastly, we critically assess literature on ion channel expression to determine whether action potentials can be initiated in T-tubules.
Collapse
|
2
|
van Opbergen CJ, van der Voorn SM, Vos MA, de Boer TP, van Veen TA. Cardiac Ca2+ signalling in zebrafish: Translation of findings to man. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 138:45-58. [DOI: 10.1016/j.pbiomolbio.2018.05.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 04/09/2018] [Accepted: 05/04/2018] [Indexed: 02/07/2023]
|
3
|
Sanon VP, Sawaki D, Mjaatvedt CH, Jourdan‐Le Saux C. Myocardial Tissue Caveolae. Compr Physiol 2015; 5:871-86. [DOI: 10.1002/cphy.c140050] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
|
4
|
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.
Collapse
|
5
|
Kekenes-Huskey PM, Cheng Y, Hake JE, Sachse FB, Bridge JH, Holst MJ, McCammon JA, McCulloch AD, Michailova AP. Modeling effects of L-type ca(2+) current and na(+)-ca(2+) exchanger on ca(2+) trigger flux in rabbit myocytes with realistic T-tubule geometries. Front Physiol 2012; 3:351. [PMID: 23060801 PMCID: PMC3463892 DOI: 10.3389/fphys.2012.00351] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Accepted: 08/16/2012] [Indexed: 12/26/2022] Open
Abstract
The transverse tubular system of rabbit ventricular myocytes consists of cell membrane invaginations (t-tubules) that are essential for efficient cardiac excitation-contraction coupling. In this study, we investigate how t-tubule micro-anatomy, L-type Ca2+ channel (LCC) clustering, and allosteric activation of Na+/Ca2+ exchanger by L-type Ca2+ current affects intracellular Ca2+ dynamics. Our model includes a realistic 3D geometry of a single t-tubule and its surrounding half-sarcomeres for rabbit ventricular myocytes. The effects of spatially distributed membrane ion-transporters (LCC, Na+/Ca2+ exchanger, sarcolemmal Ca2+ pump, and sarcolemmal Ca2+ leak), and stationary and mobile Ca2+ buffers (troponin C, ATP, calmodulin, and Fluo-3) are also considered. We used a coupled reaction-diffusion system to describe the spatio-temporal concentration profiles of free and buffered intracellular Ca2+. We obtained parameters from voltage-clamp protocols of L-type Ca2+ current and line-scan recordings of Ca2+ concentration profiles in rabbit cells, in which the sarcoplasmic reticulum is disabled. Our model results agree with experimental measurements of global Ca2+ transient in myocytes loaded with 50 μM Fluo-3. We found that local Ca2+ concentrations within the cytosol and sub-sarcolemma, as well as the local trigger fluxes of Ca2+ crossing the cell membrane, are sensitive to details of t-tubule micro-structure and membrane Ca2+ flux distribution. The model additionally predicts that local Ca2+ trigger fluxes are at least threefold to eightfold higher than the whole-cell Ca2+ trigger flux. We found also that the activation of allosteric Ca2+-binding sites on the Na+/Ca2+ exchanger could provide a mechanism for regulating global and local Ca2+ trigger fluxes in vivo. Our studies indicate that improved structural and functional models could improve our understanding of the contributions of L-type and Na+/Ca2+ exchanger fluxes to intracellular Ca2+ dynamics.
Collapse
|
6
|
Pfleger C, Ebeling G, Bläsche R, Patton M, Patel HH, Kasper M, Barth K. Detection of caveolin-3/caveolin-1/P2X7R complexes in mice atrial cardiomyocytes in vivo and in vitro. Histochem Cell Biol 2012; 138:231-41. [PMID: 22585038 DOI: 10.1007/s00418-012-0961-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/09/2012] [Indexed: 12/21/2022]
Abstract
Caveolae and caveolins, structural components of caveolae, are associated with specific ion channels in cardiac myocytes. We have previously shown that P2X purinoceptor 7 (P2X7R), a ligand-gated ion channel, is increased in atrial cardiomyocytes of caveolin-1 knockout mice; however, the specific biochemical relationship of P2X7R with caveolins in the heart is not clear. The aim of this work was to study the presence of the P2X7R in atrial cardiomyocytes and its biochemical relationship to caveolin-1 and caveolin-3. Caveolin isoforms and P2X7R were predominantly localized in buoyant membrane fractions (lipid rafts/caveolae) prepared from hearts using detergent-free sucrose gradient centrifugation. Caveolin-1 knockout mice showed normal distribution of caveolin-3 and P2X7R to buoyant membranes indicating the importance of caveolin-3 to formation of caveolae. Using clear native-PAGE, we showed that caveolin-1, -3 and P2X7R contribute to the same protein complex in the membranes of murine cardiomyocytes and in the immortal cardiomyocyte cell line HL-1. Western blot analysis revealed increased caveolin-1 and -3 proteins in tissue homogenates of P2X7R knockout mice. Finally, tissue homogenates of atrial tissues from caveolin-3 knockout mice showed elevated mRNA for P2X7R in atria. The colocalization of caveolins with P2X7R in a biochemical complex and compensated upregulation of P2X7R or caveolins in the absence of any component of the complex suggests P2X7R and caveolins may serve an important regulatory control point for disease pathology in the heart.
Collapse
Affiliation(s)
- Claudia Pfleger
- Department of Anatomy, Medical Faculty, Institute of Anatomy, University of Technology Dresden, TU Dresden, Fetscherstr. 76, 01307 Dresden, Germany
| | | | | | | | | | | | | |
Collapse
|
7
|
Abstract
Caveolins serve as a platform in plasma membrane associated caveolae to orchestrate various signaling molecules to effectively communicate extracellular signals into the interior of cell. All three types of caveolin, Cav-1, Cav-2 and Cav-3 are expressed throughout the cardiovascular system especially by the major cell types involved including endothelial cells, cardiac myocytes, smooth muscle cells and fibroblasts. The functional significance of caveolins in the cardiovascular system is evidenced by the fact that caveolin loss leads to the development of severe cardiac pathology. Caveolin gene mutations are associated with altered expression of caveolin protein and inherited arrhythmias. Altered levels of caveolins and related downstream signaling molecules in cardiomyopathies validate the integral participation of caveolin in normal cardiac physiology. This chapter will provide an overview of the role caveolins play in cardiovascular disease. Furthering our understanding of the role for caveolins in cardiovascular pathophysiology has the potential to lead to the manipulation of caveolins as novel therapeutic targets.
Collapse
|
8
|
Schulson MN, Scriven DRL, Fletcher P, Moore EDW. Couplons in rat atria form distinct subgroups defined by their molecular partners. J Cell Sci 2011; 124:1167-74. [PMID: 21385843 DOI: 10.1242/jcs.080929] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Standard local control theory, which describes Ca(2+) release during excitation-contraction coupling (ECC), assumes that all ryanodine receptor 2 (RyR2) complexes are equivalent. Findings from our laboratory have called this assumption into question. Specifically, we have shown that the RyR2 complexes in ventricular myocytes are different, depending on their location within the cell. This has led us to hypothesize that similar differences occur within the rat atrial cell. To test this hypothesis, we have triple-labelled enzymatically isolated fixed myocytes to examine the distribution and colocalization of RyR2, calsequestrin (Casq), voltage-gated Ca(2+) channels (Ca(v)1.2), the sodium-calcium exchanger (Ncx) and caveolin-3 (Cav3). A number of different surface RyR2 populations were identified, and one of these groups, in which RyR2, Ca(v)1.2 and Ncx colocalized, might provide the structural basis for 'eager' sites of Ca(2+) release in atria. A small percentage of the dyads containing RyR2 and Ca(v)1.2 were colocalized with Cav3, and therefore could be influenced by the signalling molecules it anchors. The majority of the RyR2 clusters were tightly linked to Ca(v)1.2, and, whereas some were coupled to both Ca 1.2 and Ncx, none were with Ncx alone. This suggests that Ca(v)1.2-mediated Ca(2+) -induced Ca(2+) release is the primary method of ECC. The two molecules studied that were found in the interior of atrial cells, RyR2 and Casq, showed significantly less colocalization and a reduced nearest-neighbour distance in the interior, compared with the surface of the cell. These differences might result in a higher excitability for RyR2 in the interior of the cells, facilitating the spread of excitation from the periphery to the centre. We also present morphometric data for all of the molecules studied, as well as for those colocalizations found to be significant.
Collapse
Affiliation(s)
- Meredith N Schulson
- Department of Cellular and Physiological Sciences, University of British Columbia, Life Sciences Institute, 2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada
| | | | | | | |
Collapse
|
9
|
Gershome C, Lin E, Kashihara H, Hove-Madsen L, Tibbits GF. Colocalization of voltage-gated Na+ channels with the Na+/Ca2+ exchanger in rabbit cardiomyocytes during development. Am J Physiol Heart Circ Physiol 2011; 300:H300-11. [DOI: 10.1152/ajpheart.00798.2010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Reverse-mode activity of the Na+/Ca2+ exchanger (NCX) has been previously shown to play a prominent role in excitation-contraction coupling in the neonatal rabbit heart, where we have proposed that a restricted subsarcolemmal domain allows a Na+ current to cause an elevation in the Na+ concentration sufficiently large to bring Ca2+ into the myocyte through reverse-mode NCX. In the present study, we tested the hypothesis that there is an overlapping expression and distribution of voltage-gated Na+ (Nav) channel isoforms and the NCX in the neonatal heart. For this purpose, Western blot analysis, immunocytochemistry, confocal microscopy, and image analyses were used. Here, we report the robust expression of skeletal Nav1.4 and cardiac Nav1.5 in neonatal myocytes. Both isoforms colocalized with the NCX, and Nav1.5-NCX colocalization was not statistically different from Nav1.4-NCX colocalization in the neonatal group. Western blot analysis also showed that Nav1.4 expression decreased by sixfold in the adult ( P < 0.01) and Nav1.1 expression decreased by ninefold ( P < 0.01), whereas Nav1.5 expression did not change. Although Nav1.4 underwent large changes in expression levels, the Nav1.4-NCX colocalization relationship did not change with age. In contrast, Nav1.5-NCX colocalization decreased ∼50% with development. Distance analysis indicated that the decrease in Nav1.5-NCX colocalization occurs due to a statistically significant increase in separation distances between Nav1.5 and NCX objects. Taken together, the robust expression of both Nav1.4 and Nav1.5 isoforms and their colocalization with the NCX in the neonatal heart provides structural support for Na+ current-induced Ca2+ entry through reverse-mode NCX. In contrast, this mechanism is likely less efficient in the adult heart because the expression of Nav1.4 and NCX is lower and the separation distance between Nav1.5 and NCX is larger.
Collapse
Affiliation(s)
- Cynthia Gershome
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby
- Child and Family Research Institute, Vancouver, British Columbia, Canada; and
| | - Eric Lin
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby
- Child and Family Research Institute, Vancouver, British Columbia, Canada; and
| | - Haruyo Kashihara
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby
- Child and Family Research Institute, Vancouver, British Columbia, Canada; and
| | - Leif Hove-Madsen
- Centro de Investigación Cardiovascular CSIC-ICCC, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
| | - Glen F. Tibbits
- Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby
- Child and Family Research Institute, Vancouver, British Columbia, Canada; and
| |
Collapse
|
10
|
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.
Collapse
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
| |
Collapse
|