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Scranton K, John S, Angelini M, Steccanella F, Umar S, Zhang R, Goldhaber JI, Olcese R, Ottolia M. Cardiac function is regulated by the sodium-dependent inhibition of the sodium-calcium exchanger NCX1. Nat Commun 2024; 15:3831. [PMID: 38714663 PMCID: PMC11076594 DOI: 10.1038/s41467-024-47850-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 04/15/2024] [Indexed: 05/10/2024] Open
Abstract
The Na+-Ca2+ exchanger (NCX1) is the dominant Ca2+ extrusion mechanism in cardiac myocytes. NCX1 activity is inhibited by intracellular Na+ via a process known as Na+-dependent inactivation. A central question is whether this inactivation plays a physiological role in heart function. Using CRISPR/Cas9, we inserted the K229Q mutation in the gene (Slc8a1) encoding for NCX1. This mutation removes the Na+-dependent inactivation while preserving transport properties and other allosteric regulations. NCX1 mRNA levels, protein expression, and protein localization are unchanged in K229Q male mice. However, they exhibit reduced left ventricular ejection fraction and fractional shortening, while displaying a prolonged QT interval. K229Q ventricular myocytes show enhanced NCX1 activity, resulting in action potential prolongation, higher incidence of aberrant action potentials, a faster decline of Ca2+ transients, and depressed cell shortening. The results demonstrate that NCX1 Na+-dependent inactivation plays an essential role in heart function by affecting both cardiac excitability and contractility.
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Affiliation(s)
- Kyle Scranton
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Scott John
- Department of Medicine, Division of Cardiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Marina Angelini
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Federica Steccanella
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Soban Umar
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Rui Zhang
- Smidt Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
| | - Joshua I Goldhaber
- Smidt Heart Institute, Cedars-Sinai Medical Center, Los Angeles, CA, USA
| | - Riccardo Olcese
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Michela Ottolia
- Department of Anesthesiology & Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA.
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Forbes PA, Kwan A, Mitchell DE, Blouin JS, Cullen KE. The Neural Basis for Biased Behavioral Responses Evoked by Galvanic Vestibular Stimulation in Primates. J Neurosci 2023; 43:1905-1919. [PMID: 36732070 PMCID: PMC10027042 DOI: 10.1523/jneurosci.0987-22.2023] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 01/25/2023] [Accepted: 01/30/2023] [Indexed: 02/04/2023] Open
Abstract
Noninvasive electrical stimulation of the vestibular system in humans has become an increasingly popular tool with a broad range of research and clinical applications. However, common assumptions regarding the neural mechanisms that underlie the activation of central vestibular pathways through such stimulation, known as galvanic vestibular stimulation (GVS), have not been directly tested. Here, we show that GVS is encoded by VIIIth nerve vestibular afferents with nonlinear dynamics that differ markedly from those predicted by current models. GVS produced asymmetric activation of both semicircular canal and otolith afferents to the onset versus offset and cathode versus anode of applied current, that in turn produced asymmetric eye movement responses in three awake-behaving male monkeys. Additionally, using computational methods, we demonstrate that the experimentally observed nonlinear neural response dynamics lead to an unexpected directional bias in the net population response when the information from both vestibular nerves is centrally integrated. Together our findings reveal the neural basis by which GVS activates the vestibular system, establish that neural response dynamics differ markedly from current predictions, and advance our mechanistic understanding of how asymmetric activation of the peripheral vestibular system alters vestibular function. We suggest that such nonlinear encoding is a general feature of neural processing that will be common across different noninvasive electrical stimulation approaches.SIGNIFICANCE STATEMENT Here, we show that the application of noninvasive electrical currents to the vestibular system (GVS) induces more complex responses than commonly assumed. We recorded vestibular afferent activity in macaque monkeys exposed to GVS using a setup analogous to human studies. GVS evoked notable asymmetries in irregular afferent responses to cathodal versus anodal currents. We developed a nonlinear model explaining these GVS-evoked afferent responses. Our model predicts that GVS induces directional biases in centrally integrated head motion signals and establishes electrical stimuli that recreate physiologically plausible sensations of motion. Altogether, our findings provide new insights into how GVS activates the vestibular system, which will be vital to advancing new clinical and biomedical applications.
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Affiliation(s)
- Patrick A Forbes
- Department of Neuroscience, Erasmus MC, University Medical Center Rotterdam, 3000 CA Rotterdam, The Netherlands
| | | | | | - Jean-Sébastien Blouin
- School of Kinesiology, University of British Columbia, Vancouver, British Colombia V6T 1Z1, Canada
| | - Kathleen E Cullen
- Physiology, McGill University, Montréal, Québec H3G 1Y6, Canada
- Departments of Biomedical Engineering
- Otolaryngology-Head and Neck Surgery
- Neuroscience, Johns Hopkins University, Baltimore, Maryland 21205
- Kavli Neuroscience Discovery Institute, Johns Hopkins University, Baltimore, Maryland 21205
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3
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Sciorio R, Miranian D, Smith GD. Non-invasive oocyte quality assessment. Biol Reprod 2022; 106:274-290. [PMID: 35136962 DOI: 10.1093/biolre/ioac009] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Revised: 01/04/2022] [Accepted: 01/11/2022] [Indexed: 12/27/2022] Open
Abstract
Oocyte quality is perhaps the most important limiting factor in female fertility; however, the current methods of determining oocyte competence are only marginally capable of predicting a successful pregnancy. We aim to review the predictive value of non-invasive techniques for the assessment of human oocytes and their related cells and biofluids that pertain to their developmental competence. Investigation of the proteome, transcriptome, and hormonal makeup of follicular fluid, as well as cumulus-oocyte complexes are currently underway; however, prospective randomized non-selection-controlled trials of the future are needed before determining their prognostic value. The biological significance of polar body morphology and genetics are still unknown and the subject of debate. The predictive utility of zygotic viscoelasticity for embryo development has been demonstrated, but similar studies performed on oocytes have yet to be conducted. Metabolic profiling of culture media using human oocytes are also limited and may require integration of automated, high-throughput targeted metabolomic assessments in real time with microfluidic platforms. Light exposure to oocytes can be detrimental to subsequent development and utilization of time-lapse imaging and morphometrics of oocytes is wanting. Polarized light, Raman microspectroscopy, and coherent anti-Stokes Raman scattering are a few novel imaging tools that may play a more important role in future oocyte assessment. Ultimately, the integration of chemistry, genomics, microfluidics, microscopy, physics, and other biomedical engineering technologies into the basic studies of oocyte biology, and in testing and perfecting practical solutions of oocyte evaluation, are the future for non-invasive assessment of oocytes.
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Affiliation(s)
- Romualdo Sciorio
- Edinburgh Assisted Conception Programme, EFREC, Royal Infirmary of Edinburgh, Edinburgh, UK
| | - Daniel Miranian
- Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI, USA
| | - Gary D Smith
- Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI, USA.,Department of Physiology, Urology, and Reproductive Sciences Program, University of Michigan, Ann Arbor, MI, USA
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Schick BM, Dlugas H, Czeiszperger TL, Matus AR, Bukowski MJ, Chung CS. Reduced preload increases Mechanical Control (strain-rate dependence) of Relaxation by modifying myosin kinetics. Arch Biochem Biophys 2021; 707:108909. [PMID: 34015323 PMCID: PMC8635462 DOI: 10.1016/j.abb.2021.108909] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Revised: 04/09/2021] [Accepted: 04/30/2021] [Indexed: 12/16/2022]
Abstract
Rapid myocardial relaxation is essential in maintaining cardiac output, and impaired relaxation is an early indicator of diastolic dysfunction. While the biochemical modifiers of relaxation are well known to include calcium handling, thin filament activation, and myosin kinetics, biophysical and biomechanical modifiers can also alter relaxation. We have previously shown that the relaxation rate is increased by an increasing strain rate, not a reduction in afterload. The slope of the relaxation rate to strain rate relationship defines Mechanical Control of Relaxation (MCR). To investigate MCR further, we performed in vitro experiments and computational modeling of preload-adjustment using intact rat cardiac trabeculae. Trabeculae studies are often performed using isometric (fixed-end) muscles at optimal length (Lo, length producing maximal developed force). We determined that reducing muscle length from Lo increased MCR by 20%, meaning that reducing preload could substantially increase the sensitivity of the relaxation rate to the strain rate. We subsequently used computational modeling to predict mechanisms that might underlie this preload-dependence. Computational modeling was not able to fully replicate experimental data, but suggested that thin-filament properties are not sufficient to explain preload-dependence of MCR because the model required the thin-filament to become more activated at reduced preloads. The models suggested that myosin kinetics may underlie the increase in MCR at reduced preload, an effect that can be enhanced by force-dependence. Relaxation can be modified and enhanced by reduced preload. Computational modeling implicates myosin-based targets for treatment of diastolic dysfunction, but further model refinements are needed to fully replicate experimental data.
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Affiliation(s)
- Brianna M Schick
- Department of Physiology, Wayne State University, Detroit, MI, USA
| | - Hunter Dlugas
- Department of Physiology, Wayne State University, Detroit, MI, USA
| | | | | | | | - Charles S Chung
- Department of Physiology, Wayne State University, Detroit, MI, USA.
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5
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Wang Y, Tanner BCW, Lombardo AT, Tremble SM, Maughan DW, Vanburen P, Lewinter MM, Robbins J, Palmer BM. Cardiac myosin isoforms exhibit differential rates of MgADP release and MgATP binding detected by myocardial viscoelasticity. J Mol Cell Cardiol 2012; 54:1-8. [PMID: 23123290 DOI: 10.1016/j.yjmcc.2012.10.010] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Revised: 10/05/2012] [Accepted: 10/22/2012] [Indexed: 01/26/2023]
Abstract
We measured myosin crossbridge detachment rate and the rates of MgADP release and MgATP binding in mouse and rat myocardial strips bearing one of the two cardiac myosin heavy chain (MyHC) isoforms. Mice and rats were fed an iodine-deficient, propylthiouracil diet resulting in ~100% expression of β-MyHC in the ventricles. Ventricles of control animals expressed ~100% α-MyHC. Chemically-skinned myocardial strips prepared from papillary muscle were subjected to sinusoidal length perturbation analysis at maximum calcium activation pCa 4.8 and 17°C. Frequency characteristics of myocardial viscoelasticity were used to calculate crossbridge detachment rate over 0.01 to 5mM [MgATP]. The rate of MgADP release, equivalent to the asymptotic value of crossbridge detachment rate at high MgATP, was highest in mouse α-MyHC (111.4±6.2s(-1)) followed by rat α-MyHC (65.0±7.3s(-1)), mouse β-MyHC (24.3±1.8s(-1)) and rat β-MyHC (15.5±0.8s(-1)). The rate of MgATP binding was highest in mouse α-MyHC (325±32 mM(-1) s(-1)) then mouse β-MyHC (152±23 mM(-1) s(-1)), rat α-MyHC (108±10 mM(-1) s(-1)) and rat β-MyHC (55±6 mM(-1) s(-1)). Because the events of MgADP release and MgATP binding occur in a post power-stroke state of the myosin crossbridge, we infer that MgATP release and MgATP binding must be regulated by isoform- and species-specific structural differences located outside the nucleotide binding pocket, which is identical in sequence for these four myosins. We postulate that differences in the stiffness profile of the entire myosin molecule, including the thick filament and the myosin-actin interface, are primarily responsible for determining the strain on the nucleotide binding pocket and the subsequent differences in the rates of nucleotide release and binding observed among the four myosins examined here.
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Affiliation(s)
- Yuan Wang
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA
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ter Keurs HEDJ. The interaction of Ca2+ with sarcomeric proteins: role in function and dysfunction of the heart. Am J Physiol Heart Circ Physiol 2012; 302:H38-50. [PMID: 22021327 PMCID: PMC3334233 DOI: 10.1152/ajpheart.00219.2011] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Accepted: 10/11/2011] [Indexed: 12/28/2022]
Abstract
The hallmarks of the normal heartbeat are both rapid onset of contraction and rapid relaxation as well as an inotropic response to both increased end-diastolic volume and increased heart rate. At the microscopic level, Ca(2+) plays a crucial role in normal cardiac contraction. This paper reviews the cycle of Ca(2+) fluxes during the normal heartbeat, which underlie the coupling between excitation and contraction and permit a highly synchronized action of cardiac sarcomeres. Length dependence of the response of the regulatory sarcomeric proteins mediates the Frank-Starling Law of the heart. However, Ca(2+) transport may go astray in heart disease such as in congestive heart failure, and both jeopardize systole and diastole and triggering arrhythmias. The interaction between weak and strong segments in nonuniform cardiac muscle allows partial preservation of force of contraction but may further lead to mechanoelectric feedback or reverse excitation-contraction coupling mediating an early diastolic Ca(2+) transient caused by the rapid force decrease during the relaxation phase. These rapid force changes in nonuniform muscle may cause arrhythmogenic Ca(2+) waves to propagate by the activation of neighboring sarcoplasmic reticulum by diffusing Ca(2+) ions.
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8
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Glenn TK, Honar H, Liu H, ter Keurs HEDJ, Lee SS. Role of cardiac myofilament proteins titin and collagen in the pathogenesis of diastolic dysfunction in cirrhotic rats. J Hepatol 2011; 55:1249-55. [PMID: 21703204 DOI: 10.1016/j.jhep.2011.02.030] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2010] [Revised: 02/01/2011] [Accepted: 02/16/2011] [Indexed: 02/09/2023]
Abstract
BACKGROUND & AIMS Significance of diastolic dysfunction in cirrhotic cardiomyopathy has been brought to the forefront with several reports of unexpected heart failure following liver transplantation and transjugular intrahepatic portosystemic stent-shunt, but the etiology remains unclear. The present study investigated the role of passive tension regulators - titin and collagen - in the pathogenesis of this condition. METHODS Cirrhosis was induced by bile duct ligation (BDL) in rats, while controls underwent bile duct inspection with no ligation. Four weeks after operation, cardiac mRNA and protein levels of titin, collagen, and protein kinase A (PKA) were determined. Diastolic function was examined in isolated right ventricular cardiomyocytes, while passive tension was examined in right ventricular trabeculae muscles. RESULTS In BDL animals, diastolic return velocity was significantly decreased, relaxation time increased and passive tension increased. However, no significant difference in mRNA and protein levels of titin was observed. PKA mRNA and protein levels were significantly decreased in BDL animals. Collagen levels were also significantly altered in the BDL group. CONCLUSIONS Therefore, diastolic dysfunction exists in cirrhosis with alterations in titin modulation, PKA levels, and collagen configuration contributing to the pathogenesis of this condition.
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9
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Chung CS, Methawasin M, Nelson OL, Radke MH, Hidalgo CG, Gotthardt M, Granzier HL. Titin based viscosity in ventricular physiology: an integrative investigation of PEVK-actin interactions. J Mol Cell Cardiol 2011; 51:428-34. [PMID: 21708170 DOI: 10.1016/j.yjmcc.2011.06.006] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Revised: 06/04/2011] [Accepted: 06/08/2011] [Indexed: 01/18/2023]
Abstract
Viscosity is proposed to modulate diastolic function, but only limited understanding of the source(s) of viscosity exists. In vitro experiments have shown that the proline-glutamic acid-valine-lysine (PEVK) rich element of titin interacts with actin, causing a viscous force in the sarcomere. It is unknown whether this mechanism contributes to viscosity in vivo. We tested the hypothesis that PEVK-actin interaction causes cardiac viscosity and is important in vivo via an integrative physiological study on a unique PEVK knockout (KO) model. Both skinned cardiomyocytes and papillary muscle fibers were isolated from wildtype (WT) and PEVK KO mice and passive viscosity was examined using stretch-hold-release and sinusoidal analysis. Viscosity was reduced by ~60% in KO myocytes and ~50% in muscle fibers at room temperature. The PEVK-actin interaction was not modulated by temperature or diastolic calcium, but was increased by lattice compression. Stretch-hold and sinusoidal frequency protocols on intact isolated mouse hearts showed a smaller, 30-40% reduction in viscosity, possibly due to actomyosin interactions, and showed that microtubules did not contribute to viscosity. Transmitral Doppler echocardiography similarly revealed a 40% decrease in LV chamber viscosity in the PEVK KO in vivo. This integrative study is the first to quantify the influence of a specific molecular (PEVK-actin) viscosity in vivo and shows that PEVK-actin interactions are an important physiological source of viscosity.
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Affiliation(s)
- Charles S Chung
- Molecular Cardiovascular Research Program, Sarver Heart Center, Department of Physiology, University of Arizona, Tucson, AZ 85724, USA
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King NMP, Methawasin M, Nedrud J, Harrell N, Chung CS, Helmes M, Granzier H. Mouse intact cardiac myocyte mechanics: cross-bridge and titin-based stress in unactivated cells. ACTA ACUST UNITED AC 2011; 137:81-91. [PMID: 21187335 PMCID: PMC3010058 DOI: 10.1085/jgp.201010499] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
A carbon fiber-based cell attachment and force measurement system was used to measure the diastolic stress-sarcomere length (SL) relation of mouse intact cardiomyocytes, before and after the addition of actomyosin inhibitors (2,3-butanedione monoxime [BDM] or blebbistatin). Stress was measured during the diastolic interval of twitching myocytes that were stretched at 100% base length/second. Diastolic stress increased close to linear from 0 at SL 1.85 µm to 4.2 mN/mm(2) at SL 2.1 µm. The actomyosin inhibitors BDM and blebbistatin significantly lowered diastolic stress by ∼1.5 mN/mm(2) (at SL 2.1 µm, ∼30% of total), suggesting that during diastole actomyosin interaction is not fully switched off. To test this further, calcium sensitivity of skinned myocytes was studied under conditions that simulate diastole: 37°C, presence of Dextran T500 to compress the myofilament lattice to the physiological level, and [Ca(2+)] from below to above 100 nM. Mean active stress was significantly increased at [Ca(2+)] > 55 nM (pCa 7.25) and was ∼0.7 mN/mm(2) at 100 nM [Ca(2+)] (pCa 7.0) and ∼1.3 mN/mm(2) at 175 nM Ca(2+) (pCa 6.75). Inhibiting active stress in intact cells attached to carbon fibers at their resting SL and stretching the cells while first measuring restoring stress (pushing outward) and then passive stress (pulling inward) made it possible to determine the passive cell's mechanical slack SL as ∼1.95 µm and the restoring stiffness and passive stiffness of the cells around the slack SL each as ∼17 mN/mm(2)/µm/SL. Comparison between the results of intact and skinned cells shows that titin is the main contributor to restoring stress and passive stress of intact cells, but that under physiological conditions, calcium sensitivity is sufficiently high for actomyosin interaction to contribute to diastolic stress. These findings are relevant for understanding diastolic function and for future studies of diastolic heart failure.
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Affiliation(s)
- Nicholas M P King
- Department of Physiology and Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85724, USA. granzier@email.arizona.edu
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Electromechanical coupling in the cardiac myocyte; stretch-arrhythmia feedback. Pflugers Arch 2011; 462:165-75. [PMID: 21373861 DOI: 10.1007/s00424-011-0944-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Revised: 02/16/2011] [Accepted: 02/17/2011] [Indexed: 12/29/2022]
Abstract
The macroscopic hallmarks of the normal heartbeat are rapid onset of contraction and rapid relaxation and an inotropic response to both increased end diastolic volume and increased heart rate. At the microscopic level, the calcium ion (Ca(2+)) plays a crucial role in normal cardiac contraction. This paper reviews the cycle of Ca(2+) fluxes during the normal heartbeat, which underlie the coupling between excitation and contraction (ECC) and permit a highly synchronized action of cardiac sarcomeres. Length dependence of the response of the regulatory sarcomeric proteins mediates the Frank-Starling Law of the heart. However, Ca(2+) transport may go astray in heart disease and both jeopardize the exquisite mechanism of systole and diastole and triggering arrhythmias. The interplay between weakened and strong segments in nonuniform cardiac muscle may further lead to mechanoelectric feedback-or reverse excitation contraction coupling (RECC) mediating an early diastolic Ca(2+) transient caused by the rapid force decrease during the relaxation phase. These rapid force changes in nonuniform muscle may cause arrhythmogenic Ca(2+) waves to propagate by activation of neighbouring SR by diffusing Ca(2+) ions.
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12
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Han JC, Taberner AJ, Nielsen PMF, Kirton RS, Ward ML, Loiselle DS. Energetics of stress production in isolated cardiac trabeculae from the rat. Am J Physiol Heart Circ Physiol 2010; 299:H1382-94. [PMID: 20729397 DOI: 10.1152/ajpheart.00454.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The heat liberated upon stress production in isolated cardiac muscle provides insights into the complex thermodynamic processes underlying mechanical contraction. To that end, we simultaneously measured the heat and stress (force per cross-sectional area) production of cardiac trabeculae from rats using a flow-through micromechanocalorimeter. In a flowing stream of O(2)-equilibrated Tyrode solution (∼22°C), the stress and heat production of actively contracting trabeculae were varied by 1) altering stimulus frequency (0.2-4 Hz) at optimal muscle length (L(o)), 2) reducing muscle length below L(o) at 0.2 and 2 Hz, and 3) changing extracellular Ca(2+) concentrations ([Ca(2+)](o); 1 and 2 mM). Linear regression lines were adequate to fit the active heat-stress data. The active heat-stress relationships were independent of stimulus frequency and muscle length but were dependent on [Ca(2+)](o), having greater intercepts at 2 mM [Ca(2+)](o) than at 1 mM [Ca(2+)](o) (3.5 and 2.0 kJ·m(-3)·twitch(-1), respectively). The slopes among the heat-stress relationships did not differ. At the highest experimental stimulus frequency, pronounced elevation of diastolic Ca(2+) resulted in incomplete twitch relaxation. The resulting increase of diastolic stress, which occurred with negligible metabolic energy expenditure, subsequently diminished due to the time-dependent loss of myofilament Ca(2+)-sensitivity.
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Affiliation(s)
- June-Chiew Han
- Auckland Bioengineering Institute, The Univ. of Auckland, Auckland, New Zealand.
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Dewey S, Xu Q, Gomes A. Static and dynamic properties of the HCM myocardium. J Mol Cell Cardiol 2010; 49:715-8. [PMID: 20705073 DOI: 10.1016/j.yjmcc.2010.07.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Accepted: 07/25/2010] [Indexed: 01/02/2023]
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Thompson RB, Paterson I, Chow K, Cheng-Baron J, Scott JM, Esch BT, Ennis DB, Haykowsky MJ. Characterization of the relationship between systolic shear strain and early diastolic shear strain rates: insights into torsional recoil. Am J Physiol Heart Circ Physiol 2010; 299:H898-907. [PMID: 20562339 DOI: 10.1152/ajpheart.00353.2010] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Early diastolic left ventricular (LV) untwisting has been evaluated as a manifestation of LV recoil, reflecting the release of elastic energy stored during systole. The primary goal of this study was to characterize the relationship between systolic strain (e.g., circumferential strain and the shear strains that comprise twist) with the resulting early diastolic shear strain rates, including the rate of untwisting. A further goal was to characterize these relationships regionally from apical to basal locations. Cardiac magnetic resonance imaging tissue tagging was used to measure circumferential strain, global and regional (apex, mid, basal) twist (theta), and circumferential-longitudinal (epsilon(CL)) and circumferential-radial (epsilon(CR)) shear strains along with the corresponding untwisting rates (dtheta/dt) and diastolic shear strain rates (depsilon/dt) in 32 healthy males (33 +/- 7 yr). LV untwisting rates and shear strain rates measured during early diastole varied significantly with the measurement location from apex to base (P < 0.001) but demonstrated significant linear correlation with their corresponding preceding systolic strains (P < 0.001). Untwisting rates and diastolic shear strain rates were not significantly correlated with circumferential systolic strain or end-systolic volume (P > 0.05). Normalization of the untwisting rates to the peak twist (dtheta/dt(Norm) = -13.6 +/- 2.1 s(-1)) or shear strain rates to peak systolic shear strain (depsilon(CL)/dt(Norm) = -15.0 +/- 5.4 s(-1), and depsilon(CR)/dt(Norm) = -14.2 +/- 7.7 s(-1)) yielded a uniform measure of early diastolic function that was similar for all shear strain and twist components and for all locations from apex to base. These findings support a linear model of torsional recoil in the healthy heart, where diastolic shear strain rates (e.g., untwisting rates) are linearly related to the corresponding preceding systolic shear stain component. Furthermore, these findings suggest that torsional recoil is uncoupled from end-systolic volumes or the associated strains, such as circumferential strain.
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Affiliation(s)
- Richard B Thompson
- Dept. of Biomedical Engineering, 1082 Research Transition Facility, Univ. of Alberta, Edmonton, AB, T6G 2V2, Canada.
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Zhang ML, Mei J, Archer LA, Obayashi M, Diao N, Stuyvers B, ter Keurs HEDJ. Effects of therapy using the Celacade system on structural and functional cardiac remodelling in rats following myocardial infarction. Can J Cardiol 2009; 25:e241-7. [PMID: 19584980 DOI: 10.1016/s0828-282x(09)70510-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND Immune modulation by the Celacade system (Vasogen Inc, Canada) decreases mortality and hospitalization in human heart failure. OBJECTIVES To study the effects of Celacade in rats on acute cytokine expression after coronary artery ligation, cardiac dimensions following myocardial infarction (MI), and systolic and diastolic function of cardiac muscle in MI. METHODS Celacade treatment was administered 14 days before coronary artery ligation and monthly after the surgery. Cytokine expression in cardiac tissue was measured on days 1 and 7 by ELISA in sham rats and in rats with MI (with or without Celacade treatment). Echocardiograms were obtained serially for 16 weeks. Force and sarcomere length (SL) were measured by strain gauge and laser diffraction in isolated right ventricle trabeculas at 16 weeks. The inotropic effect of pacing on force was quantified as F5 Hz/0.5 Hz. Diastolic dysfunction was quantified as the root mean square of spontaneous SL fluctuations. RESULTS Celacade inhibited transforming growth factor beta-1 production in the infarct area on day 7 (191.6+/-22.6 pg/mg versus 275.4+/-30.1 pg/mg; P<0.05), but did not attenuate cardiac dilation in MI. Celacade restored positive inotropism of pacing in MI (F5 Hz/0.5 Hz in Celacade, 219.1+/-46.7%; MI, 148.1+/-27.1% [P<0.05 compared with 211.4+/-37.9% in sham]). Celacade reduced diastolic dysfunction in MI (root mean square of spontaneous SL fluctuations: 121+/-15% and 143+/-19% with Celacade versus 184+/-19% and 190+/-26% without Celacade at 26 degrees C and 36 degrees C, respectively) compared with sham (100%; P<0.05). CONCLUSIONS Celacade reduces the increase of transforming growth factor beta-1 expression during the acute stage of MI in rats, but does not prevent chronic cardiac dilation. Celacade restores the positive inotropic effect of increased pacing rate in trabeculas from rat right ventricles with large MIs and reduces diastolic dysfunction.
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Affiliation(s)
- Mei Luo Zhang
- Department of Cardiovascular Sciences, Libin Cardiovascular Institute of Alberta, Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 4N1
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Ter Keurs HEDJ, Shinozaki T, Zhang YM, Wakayama Y, Sugai Y, Kagaya Y, Miura M, Boyden PA, Stuyvers BDM, Landesberg A. Sarcomere mechanics in uniform and nonuniform cardiac muscle: a link between pump function and arrhythmias. Ann N Y Acad Sci 2008; 1123:79-95. [PMID: 18375580 DOI: 10.1196/annals.1420.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Starling's law and the end-systolic pressure-volume relationship (ESPVR) reflect the effect of sarcomere length (SL) on the development of stress (sigma) and shortening by myocytes in the uniform ventricle. We show here that tetanic contractions of rat cardiac trabeculae exhibit a sigma-SL relationship at saturating [Ca2+] that depends on sarcomere geometry in a manner similar to that of skeletal sarcomeres and the existence of opposing forces in cardiac muscle shortened below slack length. The sigma-SL -[Ca2+](free) relationships (sigma-SL-Ca relationships) at submaximal [Ca2+] in intact and skinned trabeculae were similar, although the sensitivity for Ca2+ of intact muscle was higher. We analyzed the mechanisms underlying the sigma-SL-Ca relationship by using a kinetic model assuming that the rates of Tn-C Ca2+ binding and/or cross-bridge (XB) cycling are determined by either the SL, [Ca2+], or sigma. We analyzed the correlation between the model results and steady-state sigma measurements at varied SL at [Ca2+] from skinned rat cardiac trabeculae to test the hypotheses that the dominant feedback mechanism is SL-, sigma-, or [Ca2+]-dependent, and that the feedback mechanism regulates Tn-C Ca2+ affinity, XB kinetics, or the unitary XB force. The analysis strongly suggests that the feedback of the number of strong XBs to cardiac Tn-C Ca2+ affinity is the dominant mechanism regulating XB recruitment. Using this concept in a model of twitch-sigma accurately reproduced the sigma-SL-Ca relationship and the time courses of twitch sigma and the intracellular [Ca2+]i. The foregoing concept has equally important repercussions for the nonuniformly contracting heart, in which arrhythmogenic Ca2+ waves arise from weakened areas in the cardiac muscle. These Ca2+ waves can reversibly be induced with nonuniform excitation-contraction coupling (ECC) by the cycle of stretch and release in the border zone between the damaged and intact regions. Stimulus trains induced propagating Ca2+ waves and reversibly induced arrhythmias. We hypothesize that rapid force loss by the sarcomeres in the border zone during relaxation causes Ca2+ release from Tn-C and initiates Ca2+ waves propagated by the sarcoplasmic reticulum (SR). Modeling of the response of the cardiac twitch to rapid force changes using the feedback concept uniquely predicts the occurrence of [Ca2+]i transients as a result of accelerated Ca2+ dissociation from Tn-C. These results are consistent with the hypothesis that a force feedback to Ca2+ binding by Tn-C is responsible for Starling's law and the ESPVR in the uniform myocardium and leads to a surge of Ca2+ released by the myofilaments during relaxation in the nonuniform myocardium, which initiates arrhythmogenic propagating Ca2+ release by the SR.
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Affiliation(s)
- Henk E D J Ter Keurs
- Department of Physiology, School of Medicine, University of Calgary, 3330 Hospital Dr., N.W., Calgary, Alberta T2N 4N1, Canada.
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17
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ter Keurs HE, Shinozaki T, Zhang YM, Zhang ML, Wakayama Y, Sugai Y, Kagaya Y, Miura M, Boyden PA, Stuyvers BD, Landesberg A. Sarcomere mechanics in uniform and non-uniform cardiac muscle: A link between pump function and arrhythmias. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 97:312-31. [DOI: 10.1016/j.pbiomolbio.2008.02.013] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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18
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Granzier H, Labeit S. Structure-function relations of the giant elastic protein titin in striated and smooth muscle cells. Muscle Nerve 2008; 36:740-55. [PMID: 17763461 DOI: 10.1002/mus.20886] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The striated muscle sarcomere contains, in addition to thin and thick filaments, a third myofilament comprised of titin. The extensible region of titin spans the I-band region of the sarcomere and develops passive force in stretched sarcomeres. This force positions the A-bands in the middle of the sarcomere, maintains sarcomere length homogeneity and, importantly, is responsible for myocardial passive tension that determines diastolic filling. Recent work suggests that smooth muscle expresses a truncated titin isoform with a short extensible region that is predicted to develop high passive force levels. Several mechanisms for tuning the titin-based passive tension have been discovered that involve alternative splicing as well as posttranslational modification, mechanisms that are at play both during normal muscle function as well as during disease.
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Affiliation(s)
- Henk Granzier
- Department of Veterinary and Comparative Anatomy, Pharmacology Physiology, and Physiology, Washington State University, Pullman, Washington, USA
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19
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Eldstrom J, Wang Z, Xu H, Pourrier M, Ezrin A, Gibson K, Fedida D. The molecular basis of high-affinity binding of the antiarrhythmic compound vernakalant (RSD1235) to Kv1.5 channels. Mol Pharmacol 2007; 72:1522-34. [PMID: 17872968 DOI: 10.1124/mol.107.039388] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Vernakalant (RSD1235) is an investigational drug recently shown to convert atrial fibrillation rapidly and safely in patients (J Am Coll Cardiol 44:2355-2361, 2004). Here, the molecular mechanisms of interaction of vernakalant with the inner pore of the Kv1.5 channel are compared with those of the class IC agent flecainide. Initial experiments showed that vernakalant blocks activated channels and vacates the inner vestibule as the channel closes, and thus mutations were made, targeting residues at the base of the selectivity filter and in S6, by drawing on studies of other Kv1.5-selective blocking agents. Block by vernakalant or flecainide of Kv1.5 wild type and mutants was assessed by whole-cell patch-clamp experiments in transiently transfected human embryonic kidney 293 cells. The mutational scan identified several highly conserved amino acids, Thr479, Thr480, Ile502, Val505, and Val508, as important residues for affecting block by both compounds. In general, mutations in S6 increased the IC50 for block by vernakalant; I502A caused an extremely local 25-fold decrease in potency. Specific changes in the voltage-dependence of block with I502A supported the crucial role of this position. A homology model of the pore region of Kv1.5 predicted that, of these residues, only Thr479, Thr480, Val505, and Val508 are potentially accessible for direct interaction, and that mutation at additional sites studied may therefore affect block through allosteric mechanisms. For some of the mutations, the direction of changes in IC50 were opposite for vernakalant and flecainide, highlighting differences in the forces that drive drug-channel interactions.
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Affiliation(s)
- Jodene Eldstrom
- Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia, 2176 Health Sciences Mall, Vancouver BC, Canada V6T 1Z3
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20
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Abstract
Triggered activity in cardiac muscle and intracellular Ca2+ have been linked in the past. However, today not only are there a number of cellular proteins that show clear Ca2+ dependence but also there are a number of arrhythmias whose mechanism appears to be linked to Ca2+-dependent processes. Thus we present a systematic review of the mechanisms of Ca2+ transport (forward excitation-contraction coupling) in the ventricular cell as well as what is known for other cardiac cell types. Second, we review the molecular nature of the proteins that are involved in this process as well as the functional consequences of both normal and abnormal Ca2+ cycling (e.g., Ca2+ waves). Finally, we review what we understand to be the role of Ca2+ cycling in various forms of arrhythmias, that is, those associated with inherited mutations and those that are acquired and resulting from reentrant excitation and/or abnormal impulse generation (e.g., triggered activity). Further solving the nature of these intricate and dynamic interactions promises to be an important area of research for a better recognition and understanding of the nature of Ca2+ and arrhythmias. Our solutions will provide a more complete understanding of the molecular basis for the targeted control of cellular calcium in the treatment and prevention of such.
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Affiliation(s)
- Henk E D J Ter Keurs
- Department of Medicine, Physiology and Biophysics, University of Calgary, Alberta, Canada
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21
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Regitz-Zagrosek V, Brokat S, Tschope C. Role of Gender in Heart Failure with Normal Left Ventricular Ejection Fraction. Prog Cardiovasc Dis 2007; 49:241-51. [PMID: 17185112 DOI: 10.1016/j.pcad.2006.08.011] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Heart failure with normal ejection fraction (HF-NEF) is frequently believed to be more common in women than in men. However, the interaction of gender and age has rarely been analyzed in detail, and knowledge of the distinction between pre- and postmenopausal women is lacking. Some of the studies that have described a higher prevalence of HF-NEF in women relied on clinical diagnoses of HF together with normal systolic function and did not measure diastolic function. This applies to the analysis of patients hospitalized for HF and some epidemiological investigations that agree on the greater prevalence of HF-NEF in women. Population-based studies with echocardiographic determination of diastolic function have suggested equal or greater prevalence of diastolic dysfunction in men. Major risk factors for HF-NEF include hypertension, aging, obesity, diabetes, and ischemia. Hypertension is more frequent in women and can contribute to left ventricular and arterial stiffening in a gender-specific way. Aging, obesity, and diabetes affect myocardial and vascular stiffness differently and lead to different forms of myocardial hypertrophy in women and men. In contrast, ischemia may play a greater role in men. Gender differences in ventricular diastolic distensibility, in vascular stiffness and ventricular/vascular coupling, in skeletal muscle adaptation to HF, and in the perception of symptoms may contribute to a greater rate of HF-NEF in women. The underlying molecular mechanisms include gender differences in calcium handling, in the NO system, and in natriuretic peptides. Estrogen affects collagen synthesis and degradation and inhibits the renin-angiotensin system. Effects of estrogen may provide benefit to premenopausal women, and the loss of its protective mechanisms may render the heart of postmenopausal women more vulnerable. Thus, a number of molecular mechanisms can contribute to the gender differences in HF-NEF.
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Affiliation(s)
- Vera Regitz-Zagrosek
- Center for Cardiovascular Research, (CCR), Department of Cardiology and Pneumology, University Hospital Benjamin Franklin, Charite - Universitaetsmedizin Berlin, Berlin, Germany.
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22
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LeWinter MM, Wu Y, Labeit S, Granzier H. Cardiac titin: Structure, functions and role in disease. Clin Chim Acta 2007; 375:1-9. [PMID: 16904093 DOI: 10.1016/j.cca.2006.06.035] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2005] [Revised: 06/21/2006] [Accepted: 06/22/2006] [Indexed: 01/20/2023]
Abstract
Titin is a giant sarcomeric protein found in both cardiac and skeletal muscle. In the heart, the structure, functions and role of titin in disease have begun to be elucidated over the last decade. Titin's N-terminus is anchored in the Z-disk while C-terminal domains are bound to the thick filament. The I-band segment is a complex molecular spring consisting of PEVK and tandem Ig segments as well as variable N2B and N2A elements. The latter determine titin's two isoforms. N2B alone is present in the smaller and stiffer N2B isoform and both N2A and N2B elements are present in the larger, more compliant N2BA isoform. Large mammals co-express both isoforms, while normal rodents have virtually exclusively N2B titin. With sarcomere stretch, titin's I-band segment elongates and develops passive tension. Titin is the predominant determinant of cardiomyocyte passive tension over the physiologic sarcomere length range. With contraction below slack length, the thick filament drags titin in the opposite direction such that extension of the spring results in generation of a restoring force resulting in elastic recoil. In addition to its mechanical properties, a role is emerging for titin as a major biomechanical sensing and signaling molecule. Moreover, recent studies indicate that titin undergoes dynamic isoform and possibly phosphorylation changes in disease.
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Affiliation(s)
- Martin M LeWinter
- Department of Medicine and Cardiology Unit, University of Vermont, Burlington, VT, United States.
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23
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Ehrlich JR, Hoche C, Coutu P, Metz-Weidmann C, Dittrich W, Hohnloser SH, Nattel S, Gögelein H. Properties of a Time-Dependent Potassium Current in Pig Atrium: Evidence for a Role of Kv1.5 in Repolarization. J Pharmacol Exp Ther 2006; 319:898-906. [PMID: 16916995 DOI: 10.1124/jpet.106.110080] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Cardiac electrical activity is modulated by potassium currents. Pigs have been used for antiarrhythmic drug testing, but only sparse data exist regarding porcine atrial ionic electrophysiology. Here, we used electrophysiological, molecular, and pharmacological tools to characterize a prominent porcine outward K(+) current (I(K,PO)) in atrial cardiomyocytes isolated from adult pigs. I(K,PO) activated rapidly (time to peak at +60 mV; 2.1 +/- 0.2 ms), inactivated slowly (tau(f) = 45 +/- 10; tau(s) = 215 +/- 28 ms), and showed very slow recovery (tau(f) = 1.54 +/- 0.73 s; tau(s) = 7.91 +/- 1.78 s; n = 9; 36 degrees C). Activation and inactivation were voltage-dependent, and current properties were consistent with predominant K(+) conductance. Neurotoxins (heteropodatoxin, hongatoxin, and blood depressing substance) that block K(v)4.x, K(v)1.1, -1.2, -1.3, and -3.4 in a highly selective manner as well as H(2)O(2) and tetraethylammonium, did not affect the current. Drugs with K(v)1.5-blocking properties (flecainide, perhexiline, and the novel atrial-selective antiarrhythmic 2'-{2-(4-methoxyphenyl)-acetylamino-methyl}-biphenyl-2-carboxylic acid (2-pyridin-3-yl-ethyl)-amide; AVE0118) inhibited I(K,PO) (IC(50) of 132 +/- 47, 17 +/- 10, and 1.25 +/- 0.62 microM, respectively). 4-Aminopyridine suppressed the current and accelerated its decay, reducing charge carriage with an IC(50) of 39 +/- 15 microM. Porcine-specific K(v) channel subunit sequences were cloned to permit real-time quantitative reverse transcription-polymerase chain reaction on RNA extracted from isolated cardiomyocytes, which showed much greater abundance of K(v)1.5 mRNA compared with K(v)1.4, K(v)4.2, and K(v)4.3. Action potential recordings showed that I(K,PO) inhibition with 0.1 mM 4-AP delayed repolarization (e.g., action potential duration at -50 mV increased from 45 +/- 9 to 69 +/- 5 ms at 3 Hz; P < 0.05). In conclusion, porcine atrium displays a current that is involved in repolarization, inactivates more slowly than classic transient outward current, is associated with strong K(v)1.5 expression, and shows a pharmacological profile typical of K(v)1.5-dependent currents.
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Affiliation(s)
- Joachim R Ehrlich
- Division of Cardiology, J.W. Goethe-University, Theodor Stern Kai 7, 60590 Frankfurt, Germany.
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Stehle R, Solzin J, Iorga B, Gomez D, Blaudeck N, Pfitzer G. Mechanical properties of sarcomeres during cardiac myofibrillar relaxation: stretch-induced cross-bridge detachment contributes to early diastolic filling. J Muscle Res Cell Motil 2006; 27:423-34. [PMID: 16897577 DOI: 10.1007/s10974-006-9072-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Accepted: 06/16/2006] [Indexed: 12/01/2022]
Abstract
Sudden Ca2+ removal from isometrically contracting cardiac myofibrils induces a biphasic relaxation: first a slow, linear force decline during which sarcomeres remain isometric and then a rapid, exponential decay originating from sequential lengthening, i.e., successive mechanical relaxation, of individual sarcomeres (Stehle et al. 2002; Biophys J 83:2152-2162). Step-stretches were applied to the myofibrils, in order to study the mechanical properties of sarcomeres during this dynamic relaxation process. Stretch applied soon (approximately 10 ms) after Ca2+ removal accelerated the initiation of the rapid, exponential force decay and of the sequential sarcomere lengthening. After the stretch, a short, transient period (approximately 24 ms) remained, during which time force was enhanced and sarcomeres were homogenously elongated by the stretch. This period was similar to the duration of the switching-off of troponin C in myofibrils, as measured by stopped-flow. In contrast, when the stretch was applied during the rapid, exponential relaxation phase, force quickly decayed after stretch, back to the force level of isometric controls or even lower. Smaller stretches lengthened only those sarcomeres that were located at the wave front of the sequential sarcomere relaxation. The more the stretch-size was increased, the more of the contracting sarcomeres became lengthened by the stretch; those sarcomeres that were relaxed prior to stretch were barely elongated. These results indicate that the stretch accelerates myofibrillar relaxation by forcing the cross-bridges in contracting sarcomeres to detach. Subsequent rapid cross-bridge reattachment occurs during a short period after Ca2+ removal until troponin C is switched off. However, this switch off occurs approximately 5 times too fast to directly rate-limit the force relaxation under the isometric condition. After troponin C is switched off, stretching induces cross-bridge detachment without subsequent reattachment, and force rapidly decays below the isometric level. This may explain the rapid distention of the ventricular myocardium during early diastolic filling.
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Affiliation(s)
- R Stehle
- Institute of Vegetative Physiology, and Center of Molecular Medicine Cologne, University of Cologne, Robert-Koch-Str. 39, D-50931, Köln, Germany.
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Ter Keurs HEDJ, Wakayama Y, Miura M, Stuyvers BD, Boyden PA, Landesberg A. Spatial Nonuniformity of Contraction Causes Arrhythmogenic Ca2+Waves in Rat Cardiac Muscle. Ann N Y Acad Sci 2006; 1047:345-65. [PMID: 16093510 DOI: 10.1196/annals.1341.031] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Landesberg and Sideman's four state model of the cardiac cross-bridge (XB) hypothesizes a feedback of force development to Ca(2+) binding by troponin C (TnC). We have further modeled this behavior and observed that the force (F)-Ca(2+) relationship as well as the F-sarcomere length (SL) relationship and the time course of F and Ca(2+) transients in cardiac muscle can be reproduced faithfully by a single effect of F on deformation of the TnC-Ca complex and, thereby, on the dissociation rate of Ca(2+). Furthermore, this feedback predicts that rapid decline of F in the activated sarcomere causes release of Ca(2+) from TnC-Ca(2+), which is sufficient to initiate arrhythmogenic Ca(2+) release from the sarcoplasmic reticulum (SR). This work investigated the initiation of Ca(2+) waves underlying triggered propagated contractions (TPCs) in rat cardiac trabeculae under conditions that simulate functional nonuniformity caused by mechanical or ischemic local damage of the myocardium. A mechanical discontinuity along the trabeculae was created by exposing the preparation to a small constant flow jet of solution that reduces excitation-contraction coupling in myocytes within that segment. Force was measured, and SL as well as [Ca(2+)](i) were measured regionally. When the jet contained caffeine, 2,3-butanedione monoxime or low-[Ca(2+)], muscle-twitch F decreased and the sarcomeres in the exposed segment were stretched by shortening the normal regions outside the jet. During relaxation, the sarcomeres in the exposed segment shortened rapidly. Short trains of stimulation at 2.5 Hz reproducibly caused Ca(2+) waves to rise from the borders exposed to the jet. Ca(2+) waves started during F relaxation of the last stimulated twitch and propagated into segments both inside and outside of the jet. Arrhythmias, in the form of nondriven rhythmic activity, were triggered when the amplitude of the Ca(2+) wave increased by raising [Ca(2+)](o). The arrhythmias disappeared when the muscle uniformity was restored by turning the jet off. These results show that nonuniform contraction can cause Ca(2+) waves underlying TPCs, and suggest that Ca(2+) dissociated from myofilaments plays an important role in the initiation of arrhythmogenic Ca(2+) waves.
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Affiliation(s)
- Henk E D J Ter Keurs
- Department of Medicine, Health Sciences Centre, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
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Wen H, Bennett E, Epstein N, Plehn J. Magnetic resonance imaging assessment of myocardial elastic modulus and viscosity using displacement imaging and phase-contrast velocity mapping. Magn Reson Med 2005; 54:538-48. [PMID: 16086299 PMCID: PMC2886520 DOI: 10.1002/mrm.20589] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Approximately half of patients experiencing congestive heart failure present with a normal left ventricular ejection fraction. Perturbations in material properties affecting ventricular pressure/volume relationships likely play an important role in the "stiff heart syndrome" yet noninvasive tools permitting the accurate assessment of myocardial elasticity are extremely limited. We developed an MRI-based technique to examine regional left ventricular stress/strain relationships by incorporating displacement-encoding with stimulated-echoes (DENSE) and phase-contrast (PC) velocity mapping and compared regional elastic moduli (EM) and viscous delay time constants (VDTCs) (N=10) with immediate postmortem direct strain gauge measurements (N=8) and global chamber compliance (literature) in normal dogs. EMs by MRI were significantly greater in papillary muscle columns when compared with lateral wall and septal locations by MRI (7.59+/-1.65 versus 3.40+/-0.87 versus 2.55+/-0.93 kPa, P<0.0001) and were in agreement with direct strain gauge measurements (3.78+/-0.93 and 2.96+/-0.88 kPa for the lateral wall and the septum, P=ns for both versus MRI). MRI-determined VDTCs were similar in the three regions (VDTC=-1.15+/-12.37 versus 3.04+/-7.25 versus 4.17+/-5.76 ms, P=ns) and did not differ from lateral and septal wall strain gauge assessment (VDTC=3.09+/-0.40 and 4.57+/-1.86 ms, P=ns for both versus MRI). Viscoelastic measurements obtained in six normal volunteers demonstrated the feasibility of this technique in humans. Noninvasive, regional assessment of myocardial stiffness using DENSE and PC velocity mapping techniques is accurate in a canine model and feasible in humans.
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Affiliation(s)
- Han Wen
- Laboratory of Cardiac Energetics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892-1061, USA.
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Abstract
Titin is a giant protein that constitutes the third myofilament of the sarcomere. Single titin molecules anchor in the Z-disk and extend all the way to the M-line region of the sarcomere. Successive titin molecules are arranged head-to-head and tail-to-tail, providing a continuous filament along the full length of the myofibril. The majority of titin's I-band region is extensible and functions as a molecular spring that when extended develops passive force. We will discuss mechanisms for adjusting titin-based force, including alternative splicing and posttranslational modifications. Multiple biological functions can be assigned to different regions of the titin molecule. In addition to titin's role in determining passive muscle stiffness, recent evidence suggests a role in protein metabolism, compartmentalization of metabolic enzymes, binding of chaperones, and positioning of the membrane systems of the T-tubules and sarcoplasmic reticulum. We will also discuss titin-based force adjustments that occur in various muscle diseases and several disease-causing titin mutations that have been discovered. We will focus on the role of titin in heart failure patients that was recently investigated in patients with end-stage heart failure due to non-ischemic dilated cardiomyopathy. In end-stage failing hearts, compliant titin isoforms comprise a greater percentage of titin and changes in titin isoform expression in heart failure patients with DCM significantly impact diastolic filling by lowering myocardial stiffness.
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Affiliation(s)
- Henk Granzier
- Department of Veterinary and Comparative Anatomy, Washington State University, Pullman, WA 99164-6520, USA.
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Stuyvers BD, Dun W, Matkovich S, Sorrentino V, Boyden PA, ter Keurs HEDJ. Ca2+ sparks and waves in canine purkinje cells: a triple layered system of Ca2+ activation. Circ Res 2005; 97:35-43. [PMID: 15947247 PMCID: PMC4289137 DOI: 10.1161/01.res.0000173375.26489.fe] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We have investigated the subcellular spontaneous Ca2+ events in canine Purkinje cells using laser scanning confocal microscopy. Three types of Ca2+ transient were found: (1) nonpropagating Ca2+ transients that originate directly under the sarcolemma and lead to (2) small Ca2+ wavelets in a region limited to 6-microm depth under the sarcolemma causing (3) large Ca2+ waves that travel throughout the cell (CWWs). Immunocytochemical studies revealed 3 layers of Ca2+ channels: (1) channels associated with type 1 IP3 receptors (IP3R1) and type 3 ryanodine receptors (RyR3) are prominent directly under the sarcolemma; (2) type 2 ryanodine receptors (RyR2s) are present throughout the cell but virtually absent in a layer between 2 and 4 microm below the sarcolemma (Sub-SL); (3) type 3 ryanodine receptors (RyR3) is the dominant Ca2+ release channel in the Sub-SL. Simulations of both nonpropagating and propagating transients show that the generators of Ca2+ wavelets differ from those of the CWWs with the threshold of the former being less than that of the latter. Thus, Purkinje cells contain a functional and structural Ca2+ system responsible for the mechanism that translates Ca2+ release occurring directly under the sarcolemma into rapid Ca2+ release in the Sub-SL, which then initiates large-amplitude long lasting Ca2+ releases underlying CWWs. The sequence of spontaneous diastolic Ca2+ transients that starts directly under the sarcolemma and leads to Ca2+ wavelets and CWWs is important because CWWs have been shown to cause nondriven electrical activity.
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Affiliation(s)
- Bruno D Stuyvers
- Cardiovascular Research Group, Department of Medicine, Physiology and Biophysics, University of Calgary, Health Science Center/R1665, Calgary, Alberta, Canada.
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Shinozaki T, Wilkens JL, Yazawa T, Cavey MJ, ter Keurs HEDJ. The steady-state force-Ca2+ relationship in intact lobster (Homarus americanus) cardiac muscle. J Comp Physiol B 2004; 174:407-14. [PMID: 15133705 DOI: 10.1007/s00360-004-0427-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/18/2004] [Indexed: 10/26/2022]
Abstract
The heart of the decapod crustacean is activated by regular impulse bursts from the cardiac ganglion. The cardiac pump function depends on ganglionic burst frequency, burst duration, and burst impulse frequency. Here, we activated isolated lobster cardiac ostial muscle (Orbicularis ostii muscle, OOM) by stimulus trains in vitro in order to characterize the response of the contractile apparatus to [Ca2+]i. We employed stimulus trains that generate a steady state between the [Ca2+]i and force in order to estimate the Ca2+ sensitivity of myofilaments. Force and [Ca2+]i transients were simultaneously recorded using a silicon strain gauge and the fluorescence of iontophoretically microinjected fura-2 salt. We examined the effects of tetanus duration (TD), the interval between trains, and 6 microM cyclopiazonic acid, an inhibitor of the SR Ca2+ pump, on the steady-state force-[Ca2+]i relationship. The instantaneous force-[Ca2+]i relationships appeared sigmoidal (EC50 and Hill coefficient, 98.8+/-32.7 nM and 2.47+/-0.20, mean +/- SD, respectively), as did the curves superimposed after 500 ms following the start of stimulation, indicating that the force-[Ca2+]i relationship had reached a steady state at that time. Also, the maximum activated force (Fmax) was estimated using the steady-state force-[Ca2+]i relationship. Prolonged stimulus trains, decreasing the interval between recurrent trains from 5 to 2.5 s, and cyclopiazonic acid each increased the measured EC50 without changing Fmax. The EC50 correlated strongly with averaged [Ca2+]i over time. We conclude that the steady-state force-[Ca2+]i relationships in the OOM indicate cooperation between force generation and Ca2+ binding by the myofilaments. Our data also suggest the existence of a novel Ca2+-dependent mechanism which reduces Ca2+ sensitivity and accelerates relaxation of lobster cardiac muscle myofilaments.
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Affiliation(s)
- T Shinozaki
- Faculty of Medicine, Tohoku Graduate School of Medical Sciences, Sendai, Japan
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Davidoff AW, Boyden PA, Schwartz K, Michel JB, Zhang YM, Obayashi M, Crabbe D, ter Keurs HEDJ. Congestive Heart Failure after Myocardial Infarction in the Rat: Cardiac Force and Spontaneous Sarcomere Activity. Ann N Y Acad Sci 2004; 1015:84-95. [PMID: 15201151 DOI: 10.1196/annals.1302.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The causes of reduced cardiac force development in congestive heart failure (CHF) are still uncertain. We explored the subcellular mechanisms leading to decreased force development in trabeculae from rats with a myocardial infarction. We defined CHF according to clinical and pathological criteria and compared properties of trabeculae from animals with CHF (cMI) to those of animals with a myocardial scar but without evidence of CHF (uMI), and sham-operated animals. The new findings of this study on properties of cMI trabeculae are that (1) maximal twitch force following post-extrasystolic potentiation is unchanged; (2) the sensitivity of cMI trabeculae to [Ca(2+)](o) is increased; (3) spontaneous diastolic sarcomere length (SL) fluctuations (SA) are increased in cMI at all levels of SR Ca(2+) loading; and (4) SA is accompanied by a proportional reduction of F(max). The results suggest that the probability of spontaneous diastolic opening of SR Ca(2+) channels is increased in CHF. These data provide the basis for a novel mechanism underlying systolic and diastolic dysfunction as well as arrhythmias in hearts in CHF. If SA proves to be a component of myocardial dysfunction in human CHF, our thinking about therapy of the patient with CHF may be profoundly changed.
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Affiliation(s)
- A W Davidoff
- Department of Medicine, Faculty of Medicine, University of Calgary, Calgary, Alberta, T2N 4N1 Canada
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31
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Campbell KS, Patel JR, Moss RL. Cycling cross-bridges increase myocardial stiffness at submaximal levels of Ca2+ activation. Biophys J 2003; 84:3807-15. [PMID: 12770886 PMCID: PMC1302962 DOI: 10.1016/s0006-3495(03)75108-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Permeabilized multicellular preparations of canine myocardium were subjected to controlled length changes to investigate the extent to which cross-bridges augment passive stiffness components in myocardium at low levels of Ca(2+) activation. When the preparations were immersed in pCa 9.0 solution (negligible free [Ca(2+)]) they behaved as simple elastic systems (i.e., tension increased proportionately with length). In contrast, when the muscles were stretched in Ca(2+) activating solutions, tension rose much more rapidly during the initial phase of the movement than thereafter. Several lines of evidence suggest that the nonlinear response represents the displacement of populations of cycling cross-bridges that are perturbed by interfilamentary movement and take some time to recover. 1), The stiffness of the initial phase increased proportionately with the level of Ca(2+) activation. 2), The magnitude of the short-range response increased with stretch velocity. 3), The initial response was reversibly reduced by 5-mM 2,3-butanedione monoxime, a known cross-bridge inhibitor. The initial stiffness of the passive elastic (pCa 9.0) response was equivalent to the Ca(2+) dependent component at 2% (pCa approximately 6.2) of the maximal (pCa 4.5) level. These results suggest that cross-bridges may significantly affect diastolic chamber stiffness.
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Affiliation(s)
- Kenneth S Campbell
- Department of Physiology, University of Wisconsin, Madison, Wisconsin 53706, USA.
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Stuyvers BD, McCulloch AD, Guo J, Duff HJ, ter Keurs HEDJ. Effect of stimulation rate, sarcomere length and Ca(2+) on force generation by mouse cardiac muscle. J Physiol 2002; 544:817-30. [PMID: 12411526 PMCID: PMC2290620 DOI: 10.1113/jphysiol.2002.024430] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The relations between stress, stimulation rate and sarcomere length (SL) were investigated in 24 cardiac trabeculae isolated from right ventricles of mice (CF-1 males, 25-30 g) and superfused with Hepes solution ([Ca(2+)](o) = 1 mM, pH 7.4, 25 degrees C). Stress and SL were measured by a strain gauge transducer and laser diffraction technique, respectively. Stress versus stimulation frequency formed a biphasic relation (25 degrees C, [Ca(2+)](o) = 2 mM) with a minimum at 0.7-1 Hz (~15 mN mm(-2)), a 150 % decrease from 0.1 to 1 Hz (descending limb) and a 75 % increase from 1 to 5 Hz (ascending limb). Ryanodine (0.1 microM) inhibited specifically the descending limb, while nifedipine (0.1 microM) affected specifically the ascending limb. This result suggests two separate sources of Ca(2+) for stress development: (1) net Ca(2+) influx during action potentials (AP); and (2) Ca(2+) entry into the cytosol from the extracellular space during diastolic intervals; Ca(2+) from both (1) and (2) is sequestered by the SR between beats. Raising the temperature to 37 degrees C lowered the stress-frequency relation (SFR) by approximately 0-15 mN mm(-2) at each frequency. Because the amount of Ca(2+) carried by I(Ca,L) showed a approximately 3-fold increase under the same conditions, we conclude that reduced Ca(2+) loading of the SR was probably responsible for this temperature effect. A simple model of Ca(2+) fluxes addressed the mechanisms underlying the SFR. Simulation of the effect of inorganic phosphates (P(i)) on force production was incorporated into the model. The results suggested that O(2) diffusion limits force production at stimulation rates >3 Hz. The stress-SL relations from slack length (approximately 1.75 microm) to 2.25 microm showed that the passive stress-SL curve of mouse cardiac trabeculae is exponential with a steep increase at SL >2.1 microm. Active stress (at 1 Hz) increased with SL, following a curved relation with convexity toward the abscissa at [Ca(2+)] = 2 mM. At [Ca(2+)] from 4 to 12 mM, the stress-SL curves superimposed and the relation became linear, which revealed a saturation step in the activation of force production. EC coupling in mouse cardiac muscle is similar to that observed previously in the rat, although important differences exist in the Ca(2+) dependence of force development. These results may suggest a lower capacity of the SR for buffering Ca(2+), which makes the generation of force in mouse cardiac ventricle more dependent on Ca(2+) entering during action potentials, particularly at high heart rate.
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Affiliation(s)
- Bruno D Stuyvers
- University of Calgary, Health Sciences Center, Department of Medicine, Physiology & Biophysics, Alberta, Canada
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33
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Harris TS, Baicu CF, Conrad CH, Koide M, Buckley JM, Barnes M, Cooper G, Zile MR. Constitutive properties of hypertrophied myocardium: cellular contribution to changes in myocardial stiffness. Am J Physiol Heart Circ Physiol 2002; 282:H2173-82. [PMID: 12003826 DOI: 10.1152/ajpheart.00480.2001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent studies have suggested that pressure overload hypertrophy (POH) alters the viscoelastic properties of individual cardiocytes when studied in isolation. However, whether these changes in cardiocyte properties contribute causally to changes in the material properties of the cardiac muscle as a whole is unknown. Accordingly, a selective, isolated, acute change in cardiocyte constitutive properties was imposed in an in vitro system capable of measuring the resultant effect on the material properties of the composite cardiac muscle. POH caused an increase in both myocardial elastic stiffness, from 20.5 +/- 1.3 to 28.4 +/- 1.8, and viscous damping, from 15.2 +/- 1.1 to 19.8 +/- 1.5 s (normal vs. POH, P < 0.05), respectively. Recent studies have shown that cardiocyte constitutive properties could be acutely altered by depolymerizing the microtubules with colchicine. Colchicine caused a significant decrease in the viscous damping in POH muscles (19.8 +/- 1.5 s at baseline vs. 14.7 +/- 1.3 s after colchicine, P < 0.05). Therefore, myocardial material properties can be altered by selectively changing the constitutive properties of one element within this muscle tissue, the cardiocyte. Changes in the constitutive properties of the cardiocytes themselves contribute to the abnormalities in myocardial stiffness and viscosity that develop during POH.
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Affiliation(s)
- Todd S Harris
- Cardiology Section, Department of Medicine, and Gazes Cardiac Research Institute, Medical University of South Carolina and Veterans Administration Medical Center, Charleston, South Carolina 29401, USA
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Minajeva A, Neagoe C, Kulke M, Linke WA. Titin-based contribution to shortening velocity of rabbit skeletal myofibrils. J Physiol 2002; 540:177-88. [PMID: 11927678 PMCID: PMC2290211 DOI: 10.1113/jphysiol.2001.013154] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2001] [Accepted: 01/07/2002] [Indexed: 11/08/2022] Open
Abstract
The shortening velocity of skeletal muscle fibres is determined principally by actomyosin cross-bridges. However, these contractile elements are in parallel with elastic elements, whose main structural basis is thought to be the titin filaments. If titin is stretched, it may contribute to sarcomere shortening simply because it can recoil 'passively'. The titin-based contribution to shortening velocity (V(p)) was quantified in single rabbit psoas myofibrils. Non-activated specimens were rapidly released from different initial sarcomere lengths (SLs) by various step amplitudes sufficient to buckle the myofibrils; V(p) was calculated from the release amplitude and the time to slack reuptake. V(p) increased progressively (upper limit of detection, approximately 60 microm s(-1) sarcomere(-1)) between 2.0 and 3.0 microm SL, albeit more steeply than passive tension. At very low passive tension levels already (< 1-2 mN mm(-2)), V(p) could greatly exceed the unloaded shortening velocity measured in fully Ca(2+)-activated skinned rabbit psoas fibres. Degradation of titin in relaxed myofibrils by low doses of trypsin (5 min) drastically decreased V(p). In intact myofibrils, average V(p) was faster, the smaller the release step applied. Also, V(p) was much higher at 30 degrees C than at 15 degrees C (Q(10): 2.0, 3.04 or 6.15, for release steps of 150, 250 or 450 nm sarcomere(-1), respectively). Viscous forces opposing the shortening are likely to be involved in determining these effects. The results support the idea that the contractile system imposes a braking force onto the passive recoil of elastic structures. However, elastic recoil may aid active shortening during phases of high elastic energy utilization, i.e. immediately after the onset of contraction under low or zero load or during prolonged shortening from greater physiological SLs.
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Affiliation(s)
- Ave Minajeva
- Institute of Physiology and Pathophysiology, University of Heidelberg, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany
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35
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Kulke M, Fujita-Becker S, Rostkova E, Neagoe C, Labeit D, Manstein DJ, Gautel M, Linke WA. Interaction between PEVK-titin and actin filaments: origin of a viscous force component in cardiac myofibrils. Circ Res 2001; 89:874-81. [PMID: 11701614 DOI: 10.1161/hh2201.099453] [Citation(s) in RCA: 132] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The giant muscle protein titin contains a unique sequence, the PEVK domain, the elastic properties of which contribute to the mechanical behavior of relaxed cardiomyocytes. Here, human N2-B-cardiac PEVK was expressed in Escherichia coli and tested-along with recombinant cardiac titin constructs containing immunoglobulin-like or fibronectin-like domains-for a possible interaction with actin filaments. In the actomyosin in vitro motility assay, only the PEVK construct inhibited actin filament sliding over myosin. The slowdown occurred in a concentration-dependent manner and was accompanied by an increase in the number of stationary actin filaments. High [Ca(2+)] reversed the PEVK effect. PEVK concentrations >/=10 microgram/mL caused actin bundling. Actin-PEVK association was found also in actin fluorescence binding assays without myosin at physiological ionic strength. In cosedimentation assays, PEVK-titin interacted weakly with actin at 0 degrees C, but more strongly at 30 degrees C, suggesting involvement of hydrophobic interactions. To probe the interaction in a more physiological environment, nonactivated cardiac myofibrils were stretched quickly, and force was measured during the subsequent hold period. The observed force decline could be fit with a three-order exponential-decay function, which revealed an initial rapid-decay component (time constant, 4 to 5 ms) making up 30% to 50% of the whole decay amplitude. The rapid, viscous decay component, but not the slower decay components, decreased greatly and immediately on actin extraction with Ca(2+)-independent gelsolin fragment, both at physiological sarcomere lengths and beyond actin-myosin overlap. Steady-state passive force dropped only after longer exposure to gelsolin. We conclude that interaction between PEVK-titin and actin occurs in the sarcomere and may cause viscous drag during diastolic stretch of cardiac myofibrils. The interaction could also oppose shortening during contraction.
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Affiliation(s)
- M Kulke
- Institute of Physiology, University of Heidelberg, Heidelberg, Germany
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36
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Yamasaki R, Berri M, Wu Y, Trombitás K, McNabb M, Kellermayer MS, Witt C, Labeit D, Labeit S, Greaser M, Granzier H. Titin-actin interaction in mouse myocardium: passive tension modulation and its regulation by calcium/S100A1. Biophys J 2001; 81:2297-313. [PMID: 11566799 PMCID: PMC1301700 DOI: 10.1016/s0006-3495(01)75876-6] [Citation(s) in RCA: 179] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Passive tension in striated muscles derives primarily from the extension of the giant protein titin. However, several studies have suggested that, in cardiac muscle, interactions between titin and actin might also contribute to passive tension. We expressed recombinant fragments representing the subdomains of the extensible region of cardiac N2B titin (tandem-Ig segments, the N2B splice element, and the PEVK domain), and assayed them for binding to F-actin. The PEVK fragment bound F-actin, but no binding was detected for the other fragments. Comparison with a skeletal muscle PEVK fragment revealed that only the cardiac PEVK binds actin at physiological ionic strengths. The significance of PEVK-actin interaction was investigated using in vitro motility and single-myocyte mechanics. As F-actin slid relative to titin in the motility assay, a dynamic interaction between the PEVK domain and F-actin retarded filament sliding. Myocyte results suggest that a similar interaction makes a significant contribution to the passive tension. We also investigated the effect of calcium on PEVK-actin interaction. Although calcium alone had no effect, S100A1, a soluble calcium-binding protein found at high concentrations in the myocardium, inhibited PEVK-actin interaction in a calcium-dependent manner. Gel overlay analysis revealed that S100A1 bound the PEVK region in vitro in a calcium-dependent manner, and S100A1 binding was observed at several sites along titin's extensible region in situ, including the PEVK domain. In vitro motility results indicate that S100A1-PEVK interaction reduces the force that arises as F-actin slides relative to the PEVK domain, and we speculate that S100A1 may provide a mechanism to free the thin filament from titin and reduce titin-based tension before active contraction.
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Affiliation(s)
- R Yamasaki
- Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, Washington 99164-6520, USA
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37
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Rogers MW, Hedman LD, Johnson ME, Cain TD, Hanke TA. Lateral stability during forward-induced stepping for dynamic balance recovery in young and older adults. J Gerontol A Biol Sci Med Sci 2001; 56:M589-94. [PMID: 11524454 DOI: 10.1093/gerona/56.9.m589] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND Balance dysfunction related to lateral instability has been associated with falls and fall-related injuries among older individuals. Protective stepping for dynamic balance recovery requires the effective control of lateral body motion. This study investigated the relationship between aging, falls, and lateral stability during forward-induced stepping for dynamic balance recovery. METHODS Forward steps were induced by a motor-driven waist-pull system in 12 younger adults, 20 healthy community-dwelling older adult nonfallers, and 18 older adults who had reported falls. Group differences in kinetic and kinematic stepping characteristics for a range of postural disturbance magnitudes were evaluated. RESULTS Despite group similarities in anticipatory postural adjustments for minimizing lateral instability, the older fallers demonstrated significantly greater sideways body motion toward the stepping side at first-step foot contact and a more laterally directed foot placement. During the first step, forward-stepping characteristics were generally comparable between the groups, but the older fallers had an earlier liftoff time and longer step duration. CONCLUSIONS During forward-induced protective stepping, otherwise healthy older adults who had experienced falls showed particular differences in their control of lateral body motion that were not attributable to changes in anticipatory postural mechanisms. Aging changes in controlling lateral body motion during protective stepping appear to involve factors that intervene between the first-step liftoff and foot contact and/or adaptations in stepping patterns related to prior planning.
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Affiliation(s)
- M W Rogers
- Department of Physical Therapy and Human Movement Sciences, Northwestern University Medical School, 645 North Michigan Avenue, Chicago, IL 60611, USA.
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McCulloch AD, Mazhari R. Regional myocardial mechanics: integrative computational models of flow-function relations. J Nucl Cardiol 2001; 8:506-19. [PMID: 11481573 DOI: 10.1067/mnc.2001.117113] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Many cardiac disorders result in regionally altered myocardial mechanics. Although myocardial strain distributions can be measured experimentally and clinically, regional wall stresses must be computed from computational models. Combining these approaches can provide insight into the structural basis of regional dysfunction under conditions such as acute myocardial infarction and ischemia-reperfusion. Recently, 3-dimensional computational models have helped to elucidate the structural basis of the functional border zone adjacent to acutely ischemic myocardium. They have also shown that heterogeneous dysfunction in ischemic-reperfused stunned myocardium does not necessarily imply heterogeneous myofilament injury. Now that computational models are able to reproduce many complex features of the 3-dimensional patterns of regional myocardial deformation observed experimentally, we suggest possible roles for such integrative models in clinical diagnosis.
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Affiliation(s)
- A D McCulloch
- Department of Bioengineering, The Whitaker Institute for Biomedical Engineering, University of California San Diego, La Jolla, Calif 92093-0412, USA.
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40
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Hanley PJ, Young AA, LeGrice IJ, Edgar SG, Loiselle DS. 3-Dimensional configuration of perimysial collagen fibres in rat cardiac muscle at resting and extended sarcomere lengths. J Physiol 1999; 517 ( Pt 3):831-7. [PMID: 10358122 PMCID: PMC2269383 DOI: 10.1111/j.1469-7793.1999.0831s.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
1. We have used fluorescence confocal laser scanning microscopy to attain the three-dimensional (3-D) microstructure of perimysial collagen fibres over the range of sarcomere lengths (1.9-2.3 micrometers) in which passive force of cardiac muscle increases steeply. 2. A uniaxial muscle preparation (right ventricular trabecula of rat) was used so that the 3-D collagen configuration could be readily related to sarcomere length. Transmission electron microscopy showed that these preparations were structurally homologous to ventricular wall muscle. 3. Trabeculae were mounted on the stage of an inverted microscope and fixed at various sarcomere lengths. After a trabecula was stained with the fluorophore Sirius Red F3BA and embedded in resin, sequential optical sectioning enabled 3-D reconstruction of its perimysial collagen fibres. The area fraction of these fibres, determined from the cross-sections of seven trabeculae, was 10.5 +/- 3.9 % (means +/- s.d.). 4. The reconstructed 3-D images show that perimysial collagen fibres are wavy (as distinct from coiled) cords which straighten considerably as the sarcomere length is increased from 1.85 +/- 0.06 micrometer (near-resting length) to 2.3 +/- 0.04 micrometer (means +/- s.d., n = 4). These observations are consistent with the notion that the straightening of these fibres is responsible for limiting extension of the cardiac sarcomere to a length of approximately 2.3 micrometers.
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Affiliation(s)
- P J Hanley
- Department of Physiology, School of Medicine and Health Science, University of Auckland, Auckland, New Zealand.
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Abstract
1. Confocal laser scanning microscopy was used to visualize intercellular transmission of Ca2+ waves in intact rat ventricular trabeculae micro-injected with the calcium indicator fluo-3. 2. Ca2+ waves usually failed to be transmitted from cell to cell. At identified individual end-to-end cell contacts, successful transmission interspersed with failure, which sometimes occurred despite an apparent small spritz of Ca2+ between cells. The probability of cell to cell transmission (Ptran) was 0.13. 3. Ca2+ waves arose preferentially near junctions of connected cells, where connexin-43 was found, but randomly in enzymatically disconnected heart cells. 4. beta-Adrenergic stimulation significantly increased Ptran (to 0.22) and heptanol, an uncoupler of gap junction channels, significantly decreased it (to 0.045). 5. In regions of high [Ca2+]i due to damage, wave frequency decreased markedly with each cell-cell junction passed. 6. The Ca2+ permeability of cardiac gap junctions may be regulated, and the low ability of cardiac gap junctions to transmit Ca2+ may help control the spread of Ca2+ from damaged regions.
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Affiliation(s)
- C Lamont
- Departments of Physiology and Medicine, School of Medicine, University of Maryland, 655 West Baltimore Street, Baltimore, MD 21201, USA
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42
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Stuyvers BD, Miura M, Jin JP, ter Keurs HE. Ca(2+)-dependence of diastolic properties of cardiac sarcomeres: involvement of titin. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1998; 69:425-43. [PMID: 9785949 DOI: 10.1016/s0079-6107(98)00018-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The stiffness of the sarcomeres was studied during the diastolic interval of 18 stimulated (0.5 Hz) cardiac trabeculae of rat (pH 7.4; temperature = 25 degrees C). Sarcomere length (SL) and force (F) were measured using, respectively, laser diffraction techniques (resolution: 4 nm) and a silicon strain gauge (resolution: 0.63 microN). Sinusoidal perturbations (frequency = 500 Hz) were imposed to the length of the preparation. The stiffness was evaluated from the corresponding F and SL sinusoids by analysis of both signals together either in the time domain or in the frequency domain. A short burst (duration = 30 ms) of sinusoidal perturbations was repeated at 5 predetermined times during diastole providing 5 measurements of stiffness during the time interval separating two twitches. These measurements revealed that stiffness increases by approximately 30% during diastole, while a simultaneous expansion of the sarcomeres (amplitude = 10-60 nm) was detected. Measurements of the fluorescence of fura-2 under the same conditions revealed a continuous exponential decline of [Ca2+]i from 210 to 90 nM (constant of time approximately 300 ms) during diastole. In order to test the possibility that the increase of sarcomere stiffness and the decline of [Ca2+]i were coupled during diastole of intact trabeculae, we studied the effect of different free Ca(2+)-concentrations ([Ca2+]) between 1 and 430 nM on sarcomere stiffness in rat cardiac trabeculae skinned by saponin (n = 17). Stiffness was studied using 500 Hz sinusoidal perturbations of muscle length (ML). We found that, below 70 nM, the stiffness was independent of [Ca2+]; between 70 and 200 nM, the stiffness declined with increase of [Ca2+]; above 200 nM, the stiffness increased steeply with [Ca2+]. The data fitted accurately to the sum of two sigmoids (Hill functions): (1) at [Ca2+] < 200 nM the stiffness decreased with [Ca2+] (EC50 = 160 +/- 13 nM; n = -2.6 +/- 0.7) and (2) at [Ca2+] > 200 nM, stiffness increased with [Ca2+] (EC50 = 3.4 +/- 0.3 microM; n = 2.1 +/- 0.2) due to attachment of cross-bridges. From these results, it was possible to reproduce accurately the time course of diastolic stiffness observed in intact trabeculae and to predict the effect on stiffness of a spontaneous elevation of the diastolic [Ca2+]. Identical stiffness measurements were performed in 4 skinned preparations exposed to a cloned fragment of titin (Ti I-II) which has been shown to exhibit a strong interaction with F-actin in vitro. It was anticipated that Ti I-II would compete with endogenous titin for the same binding site on actin in the I-band. Below 200 nM, Ti I-II (2 microM) eliminated the Ca(2+)-dependence of stiffness. These results are consistent with the hypothesis that the Ca(2+)-sensitivity of the sarcomeres at [Ca2+] < 200 nM, i.e. where the myocytes in intact muscle operate during diastole, involves an association between titin molecules and the thin filament.
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