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Xi J, Feng HZ, Jin JP, Yuan J, Kawai M. Biomechanical evaluation of flash-frozen and cryo-sectioned papillary muscle samples by using sinusoidal analysis: cross-bridge kinetics and the effect of partial Ca 2+ activation. J Muscle Res Cell Motil 2024; 45:95-113. [PMID: 38625452 DOI: 10.1007/s10974-024-09667-7] [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: 10/30/2023] [Accepted: 02/08/2024] [Indexed: 04/17/2024]
Abstract
We examined the integrity of flash-frozen and cryo-sectioned cardiac muscle preparations (introduced by Feng and Jin, 2020) by assessing tension transients in response to sinusoidal length changes at varying frequencies (1-100 Hz) at 25 °C. Using 70-μm-thick sections, we isolated fiber preparations to study cross-bridge (CB) kinetics: preparations were activated by saturating Ca2+ as well as varying concentrations of ATP and phosphate (Pi). Our results showed that, compared to ordinary skinned fibers, in-series stiffness decreased to 1/2, which resulted in a decrease of isometric tension to 62%, but CB kinetics and Ca2+ sensitivity were little affected. The pCa study demonstrated that the rate constant of the force generation step (2πb) is proportionate to [Ca2+] at < 5 μM, suggesting that the activation mechanism can be described by a simple second order reaction. We also found that tension, stiffness, and magnitude parameters are related to [Ca2+] by the Hill equation, with a cooperativity coefficient of 4-5, which is consistent with the fact that Ca2+ activation mechanisms involve cooperative multimolecular interactions. Our results support the long-held hypothesis that Process C (Phase 2) represents the CB detachment step, and Process B (Phase 3) represents the force generation step. Moreover, we discovered that constant H may represent the work-performing step in cardiac preparations. Our experiments demonstrate excellent CB kinetics with two well-defined exponentials that can be more distinguished than those found using ordinary skinned fibers. Flash-frozen and cryo-sectioned preparations are especially suitable for multi-institutional collaborations nationally and internationally because of their ease of transportation.
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Affiliation(s)
- Jing Xi
- School of Nursing, and Medical Skill Experiment Teaching Center, Suzhou Medical College, Soochow University, Suzhou, 215006, China
- Department of Anatomy and Cell Biology, College of Medicine, University of Iowa, Iowa City, IA, 52242, USA
| | - Han-Zhong Feng
- Department of Physiology and Biophysics, University of Illinois at Chicago, 835 S Wolcott Ave, Chicago, IL, 60612, USA
| | - Jian-Ping Jin
- Department of Physiology and Biophysics, University of Illinois at Chicago, 835 S Wolcott Ave, Chicago, IL, 60612, USA
| | - Jinxiang Yuan
- The Collaborative Innovation Center, Jining Medical University, Jining, 272067, China
| | - Masataka Kawai
- Department of Anatomy and Cell Biology, College of Medicine, University of Iowa, Iowa City, IA, 52242, USA.
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Lewalle A, Campbell KS, Campbell SG, Milburn GN, Niederer SA. Functional and structural differences between skinned and intact muscle preparations. J Gen Physiol 2022; 154:e202112990. [PMID: 35045156 PMCID: PMC8929306 DOI: 10.1085/jgp.202112990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2021] [Accepted: 12/16/2021] [Indexed: 11/20/2022] Open
Abstract
Myofilaments and their associated proteins, which together constitute the sarcomeres, provide the molecular-level basis for contractile function in all muscle types. In intact muscle, sarcomere-level contraction is strongly coupled to other cellular subsystems, in particular the sarcolemmal membrane. Skinned muscle preparations (where the sarcolemma has been removed or permeabilized) are an experimental system designed to probe contractile mechanisms independently of the sarcolemma. Over the last few decades, experiments performed using permeabilized preparations have been invaluable for clarifying the understanding of contractile mechanisms in both skeletal and cardiac muscle. Today, the technique is increasingly harnessed for preclinical and/or pharmacological studies that seek to understand how interventions will impact intact muscle contraction. In this context, intrinsic functional and structural differences between skinned and intact muscle pose a major interpretational challenge. This review first surveys measurements that highlight these differences in terms of the sarcomere structure, passive and active tension generation, and calcium dependence. We then highlight the main practical challenges and caveats faced by experimentalists seeking to emulate the physiological conditions of intact muscle. Gaining an awareness of these complexities is essential for putting experiments in due perspective.
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Affiliation(s)
- Alex Lewalle
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, UK
| | - Kenneth S. Campbell
- Department of Physiology and Division of Cardiovascular Medicine, University of Kentucky, Lexington, KY
| | - Stuart G. Campbell
- Departments of Biomedical Engineering and Cellular and Molecular Physiology, Yale University, New Haven, CT
| | - Gregory N. Milburn
- Department of Physiology and Division of Cardiovascular Medicine, University of Kentucky, Lexington, KY
| | - Steven A. Niederer
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, UK
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3
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Jeon HJ, Lee H, Yoon DS, Kim BM. Dielectrophoretic force measurement of red blood cells exposed to oxidative stress using optical tweezers and a microfluidic chip. Biomed Eng Lett 2017; 7:317-323. [PMID: 30603182 DOI: 10.1007/s13534-017-0041-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 06/21/2017] [Accepted: 06/30/2017] [Indexed: 12/22/2022] Open
Abstract
Red blood cell (RBC) dysfunction is often associated with a pathological intervention, and it has been proposed as a critical risk factor for certain lethal diseases. Examining the cell viability of RBCs under various physiological conditions is essential and of importance for precise diagnosis and drug discovery in the field of medicine and pharmacy. In this paper, we report a new analytical method that employs dielectrophoretic (DEP) force measurements in absolute units to assess the viability, and potentially the functionality of RBCs. We precisely quantify the frequency-dependent DEP forces of the RBCs by using a micro-electrode embedded chip combined with optical tweezers. DEP characteristics are known to be well-correlated with the viability of biological cells, and DEP forces are measured in both fresh and long-term stored RBCs to investigate the effect that the storage period has on the cell viability. Moreover, we investigate the DEP behavior of RBCs when exposed to oxidative stress and verify whether EDTA protects the RBCs from an oxidant. From the experiments, it is found that the fresh RBCs without oxidative stress display very high DEP forces over the entire frequency range, exhibiting two cutoff frequencies. However, both the RBCs stored for the long-term period and exposed to oxidative stress reveals that there exist no significant DEP forces over the frequency range. The results indicate that the DEP forces can serve as a useful parameter to verify whether the RBCs in certain blood are fresh and not exposed to oxidative stress. Therefore, it is believed that our system can be applied to a diagnostic system to monitor the cell viability of the RBCs or other types of cells.
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Affiliation(s)
- Hee-Jae Jeon
- 1School of Biomedical Engineering, Korea University, Seongbuk-gu, Seoul, 02841 Korea.,2Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005 Korea
| | - Hyungbeen Lee
- 3Department of Biomedical Engineering, Yonsei University, Wonju, 26493 South Korea
| | - Dae Sung Yoon
- 1School of Biomedical Engineering, Korea University, Seongbuk-gu, Seoul, 02841 Korea
| | - Beop-Min Kim
- 1School of Biomedical Engineering, Korea University, Seongbuk-gu, Seoul, 02841 Korea
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4
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Brandt PW, Poggesi C. Clusters of bound Ca(2+) initiate contraction in fast skeletal muscle. Arch Biochem Biophys 2013; 552-553:60-7. [PMID: 24374032 DOI: 10.1016/j.abb.2013.12.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2013] [Revised: 12/04/2013] [Accepted: 12/17/2013] [Indexed: 11/30/2022]
Abstract
Ca(2+)-binding to troponin C ultimately controls force in muscle leading to the expectation that the two curves, pCa/force and pCa/Ca(2+) binding, will coincide. Using an improved fluorescence apparatus to measure Ca(2+)-binding, we confirm a displacement between the position and shape of the pCa/Ca(2+)-binding and pCa/force curves. This displacement may be part of a mechanism that reduces the noise inherent in the control process. There must always be some Ca(2+)-binding events even at 10 or 100nM, well below threshold for muscle contraction. To minimize the response to such random binding events we suggest that clusters of adjacent Ca(2+)-binding sites must be filled before contraction is initiated. Clusters promote the reconfiguration of the thin filament to the "On" state; this simultaneously increases thin filaments' affinity for myosin heads and of troponin C for Ca(2+) producing the highly cooperative pCa/force curve. The cluster requirement displaces the Ca(2+)-binding from the force curve as observed. The thin filament conformational changes and the accompanying affinity increases introduce a discontinuity in the pCa/Ca(2+)-binding curve. The curve, therefore, is most appropriately fit by two separate Hill equations, a simple non-cooperative one (midpoint, pK1, n1∼1) for the foot and a second cooperative one (pK2, n2∼2.5) for the upper part. With this fit pK2 is larger than pK1 as our argument requires, in contrast to fitting to the sum of two Hill equations. It also expresses the idea that there may be three states of the thin filament.
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Affiliation(s)
- Philip W Brandt
- Department of Pathology, Columbia University, NY, NY 10032, USA
| | - Corrado Poggesi
- Dipartimento di Medicina Sperimentale e Clinica, Università degli Studi di Firenze, Firenze 50134, Italy.
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Schachat F, Brandt PW. The troponin I: inhibitory peptide uncouples force generation and the cooperativity of contractile activation in mammalian skeletal muscle. J Muscle Res Cell Motil 2013; 34:83-92. [PMID: 23340900 DOI: 10.1007/s10974-013-9336-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Accepted: 01/10/2013] [Indexed: 11/26/2022]
Abstract
Hodges and his colleagues identified a 12 amino acid fragment of troponin I (TnI-ip) that inhibits Ca(2+)-activated force and reduces the effectiveness Ca(2+) as an activator. To understand the role of troponin C (TnC) in the extended cooperative interactions of thin filament activation, we compared the effect of TnI-ip with that of partial troponin TnC extraction. Both methods reduce maximal Ca(2+)-activated force and increase [Ca(2+)] required for activation. In contrast to TnC extraction, TnI-ip does not reduce the extended cooperative interactions between adjacent thin filament regulatory units as assessed by the slope of the pCa/force relationship. Additional evidence that TnI-ip does not interfere with extended cooperativity comes from studies that activate muscle by rigor crossbridges (RXBs). TnI-ip increases both the cooperativity of activation and the concentration of RXBs needed for maximal force. This shows that TnI-ip binding to TnC increases the stability of the relaxed state of the thin filament. TnI-ip, therefore, uncouples force generation from extended cooperativity in both Ca(2+) and RXB activated muscle contraction. Because maximum force can be reduced with no change-or even an increase-in cooperativity, force-generating crossbridges do not appear to be the primary activators of cooperativity between thin filament regulatory units of skeletal muscle.
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Affiliation(s)
- Fred Schachat
- Division of Physiology, Department of Cell Biology, Duke University Medical School, Box 3011, Durham, NC, 27710, USA.
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6
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The concentrations of free magnesium and free calcium ions both increase in skeletal muscle fibres entering Rigor mortis. Meat Sci 2012; 35:27-45. [PMID: 22060835 DOI: 10.1016/0309-1740(93)90068-s] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/1992] [Accepted: 08/21/1992] [Indexed: 12/18/2022]
Abstract
Metabolic inhibitors have been used to induce rigor in mammalian muscle fibres previously injected with the Ca(2+)- and Mg(2+)-binding dye arsenazo III. The spectral changes which ensue, after the onset of rigor, indicate that a large increase in intracellular free Ca(2+) occurs (to more than 10(-4)m) but that this is preceded and accompanied by a substantial increase in free Mg(2+) concentration (to 2 mm or more) presumably as a result of the decline in the ATP concentration within the cell. Fibres in rigor have been treated with the divalent cation ionophore A23187 to enable Ca(2+) and Mg(2+) to be extracted selectively from the cell by extracelluar chelating agents. Optical measurements performed during this extraction, confirm that both Ca(2+)- and Mg(2+)-binding to arsenazo III contribute to the absorption change which is recorded, whilst the treatment of relaxed fibres with the ionophore together with EDTA, produces an absorption change which, in combination with other measurements, indicates that in the sarcoplasm of the resting relaxed cell, approximately one third of the dye is complexed with Mg(2+). This indicates that the cytoplasmic free Mg(2+) concentration, prior to rigor onset, is about 0·5 mm.
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7
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Kawai M, Lu X, Hitchcock-DeGregori SE, Stanton KJ, Wandling MW. Tropomyosin period 3 is essential for enhancement of isometric tension in thin filament-reconstituted bovine myocardium. JOURNAL OF BIOPHYSICS (HINDAWI PUBLISHING CORPORATION : ONLINE) 2009; 2009:380967. [PMID: 20130792 PMCID: PMC2814127 DOI: 10.1155/2009/380967] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 05/29/2009] [Accepted: 07/05/2009] [Indexed: 05/28/2023]
Abstract
Tropomyosin (Tm) consists of 7 quasiequivalent repeats known as "periods," and its specific function may be associated with these periods. To test the hypothesis that either period 2 or 3 promotes force generation by inducing a positive allosteric effect on actin, we reconstituted the thin filament with mutant Tm in which either period 2 (Delta2Tm) or period 3 (Delta3Tm) was deleted. We then studied: isometric tension, stiffness, 6 kinetic constants, and the pCa-tension relationship. N-terminal acetylation of Tm did not cause any differences. The isometric tension in Delta2Tm remained unchanged, and was reduced to approximately 60% in Delta3Tm. Although the kinetic constants underwent small changes, the occupancy of strongly attached cross-bridges was not much different. The Hill factor (cooperativity) did not differ significantly between Delta2Tm (1.79 +/- 0.19) and the control (1.73 +/- 0.21), or Delta3Tm (1.35 +/- 0.22) and the control. In contrast, pCa(50) decreased slightly in Delta2Tm (5.11 +/- 0.07), and increased significantly in Delta3Tm (5.57 +/- 0.09) compared to the control (5.28 +/- 0.04). These results demonstrate that, when ions are present at physiological concentrations in the muscle fiber system, period 3 (but not period 2) is essential for the positive allosteric effect that enhances the interaction between actin and myosin, and increases isometric force of each cross-bridge.
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Affiliation(s)
- Masataka Kawai
- Department of Anatomy and Cell Biology, The University of Iowa, Iowa City, IA 52242, USA
| | - Xiaoying Lu
- Department of Anatomy and Cell Biology, The University of Iowa, Iowa City, IA 52242, USA
| | | | - Kristen J. Stanton
- Department of Anatomy and Cell Biology, The University of Iowa, Iowa City, IA 52242, USA
| | - Michael W. Wandling
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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8
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Tanizawa H, Taniguchi M, Ghimire GD, Mitaku S. Prediction of fragile points of coiled coils. CHEM-BIO INFORMATICS JOURNAL 2009. [DOI: 10.1273/cbij.9.12] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Hideki Tanizawa
- Department of Applied Physics, School of Engineering, Nagoya University
| | - Mieko Taniguchi
- Department of Biotechnology and Biomaterial Chemistry, Graduate School of Engineering, Nagoya University
| | - Ganga D. Ghimire
- Research Centre Juelich, Institute of Neurosciences and Biophysics, INB-2, Molecular Biophysics
| | - Shigeki Mitaku
- Department of Applied Physics, School of Engineering, Nagoya University
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9
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Jarosch R. Large-scale models reveal the two-component mechanics of striated muscle. Int J Mol Sci 2008; 9:2658-2723. [PMID: 19330099 PMCID: PMC2635638 DOI: 10.3390/ijms9122658] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2008] [Revised: 12/11/2008] [Accepted: 12/15/2008] [Indexed: 11/30/2022] Open
Abstract
This paper provides a comprehensive explanation of striated muscle mechanics and contraction on the basis of filament rotations. Helical proteins, particularly the coiled-coils of tropomyosin, myosin and alpha-actinin, shorten their H-bonds cooperatively and produce torque and filament rotations when the Coulombic net-charge repulsion of their highly charged side-chains is diminished by interaction with ions. The classical "two-component model" of active muscle differentiated a "contractile component" which stretches the "series elastic component" during force production. The contractile components are the helically shaped thin filaments of muscle that shorten the sarcomeres by clockwise drilling into the myosin cross-bridges with torque decrease (= force-deficit). Muscle stretch means drawing out the thin filament helices off the cross-bridges under passive counterclockwise rotation with torque increase (= stretch activation). Since each thin filament is anchored by four elastic alpha-actinin Z-filaments (provided with force-regulating sites for Ca(2+) binding), the thin filament rotations change the torsional twist of the four Z-filaments as the "series elastic components". Large scale models simulate the changes of structure and force in the Z-band by the different Z-filament twisting stages A, B, C, D, E, F and G. Stage D corresponds to the isometric state. The basic phenomena of muscle physiology, i. e. latency relaxation, Fenn-effect, the force-velocity relation, the length-tension relation, unexplained energy, shortening heat, the Huxley-Simmons phases, etc. are explained and interpreted with the help of the model experiments.
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Affiliation(s)
- Robert Jarosch
- Formerly Institute of Plant Physiology, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria. E-Mail:
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Shimamoto Y, Kono F, Suzuki M, Ishiwata S. Nonlinear force-length relationship in the ADP-induced contraction of skeletal myofibrils. Biophys J 2007; 93:4330-41. [PMID: 17890380 PMCID: PMC2098727 DOI: 10.1529/biophysj.107.110650] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The regulatory mechanism of sarcomeric activity has not been fully clarified yet because of its complex and cooperative nature, which involves both Ca(2+) and cross-bridge binding to the thin filament. To reveal the mechanism of regulation mediated by the cross-bridges, separately from the effect of Ca(2+), we investigated the force-sarcomere length (SL) relationship in rabbit skeletal myofibrils (a single myofibril or a thin bundle) at SL > 2.2 microm in the absence of Ca(2+) at various levels of activation by exogenous MgADP (4-20 mM) in the presence of 1 mM MgATP. The individual SLs were measured by phase-contrast microscopy to confirm the homogeneity of the striation pattern of sarcomeres during activation. We found that at partial activation with 4-8 mM MgADP, the developed force nonlinearly depended on the length of overlap between the thick and the thin filaments; that is, contrary to the maximal activation, the maximal active force was generated at shorter overlap. Besides, the active force became larger, whereas this nonlinearity tended to weaken, with either an increase in [MgADP] or the lateral osmotic compression of the myofilament lattice induced by the addition of a macromolecular compound, dextran T-500. The model analysis, which takes into account the [MgADP]- and the lattice-spacing-dependent probability of cross-bridge formation, was successfully applied to account for the force-SL relationship observed at partial activation. These results strongly suggest that the cross-bridge works as a cooperative activator, the function of which is highly sensitive to as little as <or=1 nm changes in the lattice spacing.
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Affiliation(s)
- Yuta Shimamoto
- Department of Physics, Faculty of Science and Engineering, Waseda University, Tokyo, Japan
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11
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Kawai M, Ishiwata S. Use of thin filament reconstituted muscle fibres to probe the mechanism of force generation. J Muscle Res Cell Motil 2006; 27:455-68. [PMID: 16909198 PMCID: PMC2896216 DOI: 10.1007/s10974-006-9075-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2006] [Accepted: 06/21/2006] [Indexed: 10/24/2022]
Abstract
The technique of selective removal of the thin filament by gelsolin in bovine cardiac muscle fibres, and reconstitution of the thin filament from isolated proteins is reviewed, and papers that used reconstituted preparations are discussed. By comparing the results obtained in the absence/presence of regulatory proteins tropomyosin (Tm) and troponin (Tn), it is concluded that the role of Tm and Tn in force generation is not only to expose the binding site of actin to myosin, but also to modify actin for better stereospecific and hydrophobic interaction with myosin. This conclusion is further supported by experiments that used a truncated Tm mutant and the temperature study of reconstituted fibres. The conclusion is consistent with the hypothesis that there are three states in the thin filament: blocked state, closed state, and open state. Tm is the major player to produce these effects, with Tn playing the role of Ca2+ sensing and signal transmission mechanism. Experiments that changed the number of negative charges at the N-terminal finger of actin demonstrates that this part of actin is essential to promote the strong interaction between actin and myosin molecules, in addition to the well-known weak interaction that positions the myosin head at the active site of actin prior to force generation.
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Affiliation(s)
- Masataka Kawai
- Department of Anatomy and Cell Biology, College of Medicine, The University of Iowa, Iowa City, IA 52242, USA.
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12
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Taniguchi M, Matsumoto O, Suzuki S, Nishino Y, Okuda A, Taga T, Yamane T. MgATP-induced conformational changes in a single myosin molecule observed by atomic force microscopy: periodicity of substructures in myosin rods. SCANNING 2003; 25:223-229. [PMID: 14748384 DOI: 10.1002/sca.4950250502] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
This paper discusses the conformational changes in a single myosin molecule directly observed using atomic force microscopy (AFM). The myosin molecules were pretreated in rigor solutions without MgATP or in relaxed solutions with various concentrations of MgATP. The images of these molecules were obtained using a tapping mode AFM. The results indicate that the orientation of the myosin's heads and tail strongly depend on the MgATP concentration. Without using MgATP, almost all of the myosin molecules are in the extended form; however, when MgATP is used, the molecules bend according to the level of MgATP concentration. The mean-square end-to-end distance of the myosin molecules is significantly shorter with p[MgATP] = 4 than with p[MgATP] = 6. The rod region did not show the same level of intensity along their length in the extended form. The rods exhibited clusters of discontinuity, which were identified as substructures. The size of these substructures change at intervals that are multiples of 14.3-14.5 nm, which reflects the periodicity of the alpha-helical coiled coils. The substructure clusters also correspond to the myosin crossbridge spacing in muscles (14.3 or 43 nm). These results suggest that the myosin's head bends in conjunction with the bending or tilting in the helical substructures. Conformational changes of the myosin molecule induced by MgATP seem to mimic the molecular motions in a muscle's force generation process.
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Affiliation(s)
- Mieko Taniguchi
- Department of Biotechnology, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
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Bukatina AE, Theodore LJ, Campbell KB, Sieck GC. Calcium-independent activation of skinned cardiac muscle by secophalloidin. FEBS Lett 2002; 519:201-4. [PMID: 12023045 DOI: 10.1016/s0014-5793(02)02766-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Thin filament regulation of muscle contraction is believed to be mediated by both Ca2+ and strongly bound myosin cross-bridges. We found that secophalloidin (SPH, 5-8 mM) activates cross-bridge cycling without Ca2+ causing isometric force comparable to that induced by Ca2+. At saturated [SPH], Ca2+ further increased force by 20%. SPH-induced force was reversible upon washing with a relaxing solution. However, there was more than 30% irreversible loss in subsequent Ca2+-activated force. We hypothesize that SPH activates muscle via strongly bound cross-bridges. SPH-activated contraction provides a new model for studying the role of Ca2+ and cross-bridges in muscle regulation.
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Affiliation(s)
- Anna E Bukatina
- Departments of Anesthesiology, and Physiology and Biophysics, Mayo Foundation, Jo 4-184, 200 First Street SW, Rochester, MN 55905, USA.
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14
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Abstract
Ca(2+) regulation of contraction in vertebrate striated muscle is exerted primarily through effects on the thin filament, which regulate strong cross-bridge binding to actin. Structural and biochemical studies suggest that the position of tropomyosin (Tm) and troponin (Tn) on the thin filament determines the interaction of myosin with the binding sites on actin. These binding sites can be characterized as blocked (unable to bind to cross bridges), closed (able to weakly bind cross bridges), or open (able to bind cross bridges so that they subsequently isomerize to become strongly bound and release ATP hydrolysis products). Flexibility of the Tm may allow variability in actin (A) affinity for myosin along the thin filament other than through a single 7 actin:1 tropomyosin:1 troponin (A(7)TmTn) regulatory unit. Tm position on the actin filament is regulated by the occupancy of NH-terminal Ca(2+) binding sites on TnC, conformational changes resulting from Ca(2+) binding, and changes in the interactions among Tn, Tm, and actin and as well as by strong S1 binding to actin. Ca(2+) binding to TnC enhances TnC-TnI interaction, weakens TnI attachment to its binding sites on 1-2 actins of the regulatory unit, increases Tm movement over the actin surface, and exposes myosin-binding sites on actin previously blocked by Tm. Adjacent Tm are coupled in their overlap regions where Tm movement is also controlled by interactions with TnT. TnT also interacts with TnC-TnI in a Ca(2+)-dependent manner. All these interactions may vary with the different protein isoforms. The movement of Tm over the actin surface increases the "open" probability of myosin binding sites on actins so that some are in the open configuration available for myosin binding and cross-bridge isomerization to strong binding, force-producing states. In skeletal muscle, strong binding of cycling cross bridges promotes additional Tm movement. This movement effectively stabilizes Tm in the open position and allows cooperative activation of additional actins in that and possibly neighboring A(7)TmTn regulatory units. The structural and biochemical findings support the physiological observations of steady-state and transient mechanical behavior. Physiological studies suggest the following. 1) Ca(2+) binding to Tn/Tm exposes sites on actin to which myosin can bind. 2) Ca(2+) regulates the strong binding of M.ADP.P(i) to actin, which precedes the production of force (and/or shortening) and release of hydrolysis products. 3) The initial rate of force development depends mostly on the extent of Ca(2+) activation of the thin filament and myosin kinetic properties but depends little on the initial force level. 4) A small number of strongly attached cross bridges within an A(7)TmTn regulatory unit can activate the actins in one unit and perhaps those in neighboring units. This results in additional myosin binding and isomerization to strongly bound states and force production. 5) The rates of the product release steps per se (as indicated by the unloaded shortening velocity) early in shortening are largely independent of the extent of thin filament activation ([Ca(2+)]) beyond a given baseline level. However, with a greater extent of shortening, the rates depend on the activation level. 6) The cooperativity between neighboring regulatory units contributes to the activation by strong cross bridges of steady-state force but does not affect the rate of force development. 7) Strongly attached, cycling cross bridges can delay relaxation in skeletal muscle in a cooperative manner. 8) Strongly attached and cycling cross bridges can enhance Ca(2+) binding to cardiac TnC, but influence skeletal TnC to a lesser extent. 9) Different Tn subunit isoforms can modulate the cross-bridge detachment rate as shown by studies with mutant regulatory proteins in myotubes and in in vitro motility assays. (ABSTRACT TRUNCATED)
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Affiliation(s)
- A M Gordon
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195-7290, USA.
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15
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Tesi C, Colomo F, Nencini S, Piroddi N, Poggesi C. Modulation by substrate concentration of maximal shortening velocity and isometric force in single myofibrils from frog and rabbit fast skeletal muscle. J Physiol 1999; 516 ( Pt 3):847-53. [PMID: 10200430 PMCID: PMC2269292 DOI: 10.1111/j.1469-7793.1999.0847u.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. The effects of magnesium adenosine triphosphate (MgATP; also referred to as 'substrate') concentration on maximal force and shortening velocity have been studied at 5 C in single and thin bundles of striated muscle myofibrils. The minute diameters of the preparations promote rapid diffusional equilibrium between the bathing medium and lattice space so that during contraction fine control of substrate and product concentrations is achieved. 2. Myofibrils from frog tibialis anterior and rabbit psoas fast skeletal muscles were activated maximally by rapidly (10 ms) exchanging a continuous flux of pCa 8.0 for one at pCa 4.75 at a range of substrate concentrations from 10 microM to 5 mM. At high substrate concentrations maximal isometric tension and shortening velocity of both frog and rabbit myofibrils were very close to those determined in whole fibre preparations from the same muscle types. 3. As in frog and rabbit skinned whole fibres, the maximal isometric force of the myofibril preparations decreases as MgATP concentration is increased. The maximal velocity of unloaded shortening (V0) depends hyperbolically on substrate concentration. V0 extrapolated to infinite MgATP (3.6 +/- 0.2 and 0.8 +/- 0.03 l0 s-1 in frog and rabbit myofibrils, respectively) is very close to that determined directly at high substrate concentration. The Km is 210 +/- 20 microM for frog tibialis anterior and 120 +/- 10 microM for rabbit psoas myofibrils, values about half those found in larger whole fibre preparations of the same muscle types. This implies that measurements in whole skinned fibres are perturbed by diffusional delays, even in the presence of MgATP regenerating systems. 4. In both frog and rabbit myofibrils, the Km for V0 is about one order of magnitude higher than the Km for myofibrillar MgATPase determined biochemically in the same experimental conditions. This confirms that the difference between the Km values for MgATPase and shortening velocity is a basic feature of the mechanism of chemomechanical transduction in muscle contraction.
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Affiliation(s)
- C Tesi
- Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze, Viale G. B. Morgagni 63, I-50134 Firenze, Italy.
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16
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Yamaguchi M. Modulating factors of calcium-free contraction at low [MgATP]: a physiological study on the steady states of skinned fibres of frog skeletal muscle. J Muscle Res Cell Motil 1998; 19:949-60. [PMID: 10047994 DOI: 10.1023/a:1005405002095] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Factors that modulate Ca(2+)-free contraction at low [MgATP] were examined by analysing steady tension development in skinned fibres of frog skeletal muscle. The commonly accepted bell-shaped relationship between steady tension and log (1/[MgATP]) was found to be highly susceptible to subtle experimental conditions at the higher [MgATP] side (right limb). The limb shifted to the right with increased fibre thickness, interrupted stirring of the bathing solution, increased temperature and fibre extension, although the effects of temperature and extension were marked only in thick fibres (cross-sectional area > 6000 microns 2). The shift of the right limb was reproduced by an addition of ADP to the bathing solution. These results, together with the extreme steepness of the right limb in thick fibres, suggest that a diffusion-dependent self-regenerative activation occurs in thick fibres in which ADP accumulation and ATP depletion positively feed back through further activation of the myofibrillar ATPase. Numerical simulation supported the hypothesis of the self-regenerative activation under poor diffusion conditions, and suggested that a small rise in temperature and fibre extension can trigger the self-regenerative process at the right limb. Consequently, ADP, temperature and fibre extension are deduced to be the primary potentiators of the activation at low [MgATP]. The high efficiency of ADP in shifting the limb suggests that the activating efficiency of the MgADP-bound actomyosin complex is higher than the nucleotide-free actomyosin complex.
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Affiliation(s)
- M Yamaguchi
- Department of Physiology, Jikei University School of Medicine, Tokyo, Japan.
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17
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Lehrer SS, Geeves MA. The muscle thin filament as a classical cooperative/allosteric regulatory system. J Mol Biol 1998; 277:1081-9. [PMID: 9571024 DOI: 10.1006/jmbi.1998.1654] [Citation(s) in RCA: 160] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is generally accepted that the regulation of muscle contraction involves cooperative and allosteric interactions among the protein components, actin, myosin, tropomyosin and troponin. But, as yet, the individual role of each component has not been clearly identified. Here we compare the properties of the components of the muscle regulatory system with the corresponding components of two systems, hemoglobin and aspartate transcarbamylase, that are well described by the classical Monod, Wyman and Changeux (MWC) model. The analogy indicates that actin is the catalytic subunit, tropomyosin is the regulatory subunit and troponin in the absence and presence of Ca2+ is the allosteric inhibitor and activator, respectively. The analogy additionally indicates that the substrate is myosin-ATP (or myosin-ADP-Pi) rather than ATP. Also, in contrast to other MWC systems, the activating ligand for actin-tropomyosin is a myosin-nucleotide intermediate or product that binds tightly to actin, rather than the substrate which binds weakly. This tightly bound intermediate switches the system from the off-state to the on-state (T to R-state in MWC nomenclature) in a concerted transition, affecting n actin subunits, allowing force to be developed.
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Affiliation(s)
- S S Lehrer
- Muscle Research Group, Boston Biomedical Research Institute, Boston, MA 01224, USA
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18
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Abstract
Extraction of troponin C (TnC) from skinned muscle fibers reduces maximum Ca2+ and rigor cross-bridge (RXB)-activated tensions and reduces cooperativity between neighboring regulatory units (one troponin-tropomyosin complex and the seven associated actins) of thin filaments. This suggests that TnC has a determining role in RXB, as well as in Ca(2+)-dependent activation processes. To investigate this possibility further, we replaced fast TnC (fTnC) of rabbit psoas fibers with either CaM[3,4TnC] or cardiac TnC (cTnC) and compared the effects of these substitutions on Ca2+ and RXB activation of tension. CaM[3,4TnC] substitution has the same effect on Ca(2+)- and RXB-activated tensions; they are reduced 50%, and cooperativity between regulatory units is reduced 40%. cTnC substitution also reduces the maximum Ca(2+)-activated tension and cooperativity. But with RXB activation the effects on tension and cooperativity are opposite; cTnC substitution potentiates tension but reduces cooperativity. We considered whether tension potentiation could be explained by increased activation by cycling cross-bridges (CXBs), but the concerted transition formalism predicts fibers will fail to relax in high substrate and high pCa when CXBs are activator ligands. It predicts resting tension, which is not observed in either control or cTnC-substituted fibers. Rather, it appears that cTnC facilitates RXB activation of fast fibers more effectively than fTnC. The order of RXB-activated tension facilitation is cTnC > fTnC > CaM[3,4TnC] > empty TnC-binding sites. Comparison of the structures of fTnC, CaM[3,4TnC], and cTnC indicates that the critical region for this property lies in the central helix or N-terminal domain, including EF hand motifs 1 and 2.
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Affiliation(s)
- P W Brandt
- Department of Anatomy and Cell Biology, Columbia University, New York, New York 10032, USA.
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19
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Kellermayer MS, Pollack GH. Rescue of in vitro actin motility halted at high ionic strength by reduction of ATP to submicromolar levels. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1277:107-14. [PMID: 8950375 DOI: 10.1016/s0005-2728(96)00089-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The combined effects of ATP concentration and ionic strength were studied in an actomyosin in vitro motility assay using skeletal and cardiac myosin. The velocity of actin filaments increased up to a critical ionic strength, at which filament sliding stopped. At or above the critical ionic strength, filaments did not slide, but wiggled while focally attached to the surface. At these high ionic strengths, when the ATP concentration (originally 1 mM) was progressively reduced (down to submicromolar levels) by rigor-solution washes, the stationary, wiggling actin filaments promptly started to slide. The effect was reversible; upon adding ATP again, the sliding movement stopped, and wiggling began. The ATP washout-induced motility at high ionic strength may be explained by an electrostatic mechanism which determines the affinity of myosin to actin. The critical ionic strength was different for skeletal and cardiac myosin. For skeletal it was 77 mM, while for cardiac it was only 57 mM. Cardiac myosin's lower critical ionic strength implies a lower affinity to actin.
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Affiliation(s)
- M S Kellermayer
- Center for Bioengineering, University of Washington, Seattle 98195, USA.
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20
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Suarez-Kurtz G, Catinot MP, Ponte CG, Vianna-Jorge R, Mounier Y. Effects of uridine triphosphate on skinned skeletal muscle fibers of the rat. Can J Physiol Pharmacol 1995; 73:1451-7. [PMID: 8748937 DOI: 10.1139/y95-202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Chemically skinned muscle fibers from rat extensor digitorum longus muscle were used to study the effects of uridine triphosphate (UTP) on Ca2+ uptake and release by the sarcoplasmic reticulum (SR) and on Ca2+-activated tensions. Total replacement (2.5 mM) of adenosine triphosphate (ATP) with UTP (i) increased submaximal Ca2+-induced tension (pCa 6.2-5.8) but diminished Po, the maximum tension elicited by pCa 4.2, by ca. 15%, (ii) markedly reduced Ca2+ uptake by the SR (evaluated by caffeine-elicited tension); and (iii) induced tension in Ca2+-loaded fibers. The UTP-induced tension averaged 55% of Po and its rates of development and decay were considerably slower than those of caffeine-evoked tension. The UTP-induced tension (i) depended on the Ca2+-loading conditions; (ii) was reversibly blocked by brief (15 s) exposures of Ca2+-loaded fibers to 5 mM EGTA or by pretreatment with caffeine; (iii) was abolished by functional disruption of the SR with the nonionic detergent Brij-58; and (iv) persisted after blockade of the SR Ca2+ release channels with ruthenium red. Exposure of Ca2+-loaded fibers to UTP depressed the tension elicited subsequently by caffeine, and enhanced the rate of depletion of caffeine-sensitive Ca2+ stores during soaking in relaxing solutions containing 5 mM EGTA. The UTP-induced tension is attributed to increased release of Ca2+ from the SR, via a ruthenium red insensitive pathway(s), combined with reduced Ca2+ uptake by the SR and increased Ca2+ affinity of the contractile proteins.
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Affiliation(s)
- G Suarez-Kurtz
- Departamento de Bioquimica Medica, Instituto de Ciencias Biomedicas, ICB-CCS, Universidade Federal do Rio de Janeiro, Cidade Universitaria, Rio de Janeiro, Brazil
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21
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Simon VR, Swayne TC, Pon LA. Actin-dependent mitochondrial motility in mitotic yeast and cell-free systems: identification of a motor activity on the mitochondrial surface. J Biophys Biochem Cytol 1995; 130:345-54. [PMID: 7615636 PMCID: PMC2199926 DOI: 10.1083/jcb.130.2.345] [Citation(s) in RCA: 155] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Using fluorescent membrane potential sensing dyes to stain budding yeast, mitochondria are resolved as tubular organelles aligned in radial arrays that converge at the bud neck. Time-lapse fluorescence microscopy reveals region-specific, directed mitochondrial movement during polarized yeast cell growth and mitotic cell division. Mitochondria in the central region of the mother cell move linearly towards the bud, traverse the bud neck, and progress towards the bud tip at an average velocity of 49 +/- 21 nm/sec. In contrast, mitochondria in the peripheral region of the mother cell and at the bud tip display significantly less movement. Yeast strains containing temperature sensitive lethal mutations in the actin gene show abnormal mitochondrial distribution. No mitochondrial movement is evident in these mutants after short-term shift to semi-permissive temperatures. Thus, the actin cytoskeleton is important for normal mitochondrial movement during inheritance. To determine the possible role of known myosin genes in yeast mitochondrial motility, we investigated mitochondrial inheritance in myo1, myo2, myo3 and myo4 single mutants and in a myo2, myo4 double mutant. Mitochondrial spatial arrangement and motility are not significantly affected by these mutations. We used a microfilament sliding assay to examine motor activity on isolated yeast mitochondria. Rhodamine-phalloidin labeled yeast actin filaments bind to immobilized yeast mitochondria, as well as unilamellar, right-side-out, sealed mitochondrial outer membrane vesicles. In the presence of low levels of ATP (0.1-100 microM), we observed F-actin sliding on immobilized yeast mitochondria. In the presence of high levels of ATP (500 microM-2 mM), bound filaments are released from mitochondria and mitochondrial outer membranes. The maximum velocity of mitochondria-driven microfilament sliding (23 +/- 11 nm/sec) is similar to that of mitochondrial movement in living cells. This motor activity requires hydrolysis of ATP, does not require cytosolic extracts, is sensitive to protease treatment, and displays an ATP concentration dependence similar to that of members of the myosin family of actin-based motors. This is the first demonstration of an actin-based motor activity in a defined organelle population.
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Affiliation(s)
- V R Simon
- Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York 10032, USA
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22
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Kellermayer MS, Hinds TR, Pollack GH. Persisting in vitro motility of actin filaments at nanomolar ATP concentrations after ATP pretreatment. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1995. [DOI: 10.1016/0005-2728(94)00191-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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23
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Metzger JM. Myosin binding-induced cooperative activation of the thin filament in cardiac myocytes and skeletal muscle fibers. Biophys J 1995; 68:1430-42. [PMID: 7787029 PMCID: PMC1282038 DOI: 10.1016/s0006-3495(95)80316-4] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Myosin binding-induced activation of the thin filament was examined in isolated cardiac myocytes and single slow and fast skeletal muscle fibers. The number of cross-bridge attachments was increased by stepwise lowering of the [MgATP] in the Ca(2+)-free solution bathing the preparations. The extent of thin filament activation was determined by monitoring steadystate isometric tension at each MgATP concentration. As pMgATP (where pMgATP is -log [MgATP]) was increased from 3.0 to 8.0, isometric tension increased to a peak value in the pMgATP range of 5.0-5.4. The steepness of the tension-pMgATP relationship, between the region of the curve where tension was zero and the peak tension, is hypothesized to be due to myosin-induced cooperative activation of the thin filament. Results showed that the steepness of the tension-pMgATP relationship was markedly greater in cardiac as compared with either slow or fast skeletal muscle fibers. The steeper slope in cardiac myocytes provides evidence of greater myosin binding-induced cooperative activation of the thin filament in cardiac as compared with skeletal muscle, at least under these experimental conditions of nominal free Ca2+. Cooperative activation is also evident in the tension-pCa relation, and is dependent upon thin filament molecular interactions, which require the presence of troponin C. Thus, it was determined whether myosin-based cooperative activation of the thin filament also requires troponin C. Partial extraction of troponin C reduced the steepness of the tension-pMgATP relationship, with the effect being significantly greater in cardiac than in skeletal muscle. After partial extraction of troponin C, muscle type differences in the steepness of the tension-pMgATP relationship were no longer apparent, and reconstitution with purified troponin C restored the muscle lineage differences. These results suggest that, in the absence of Ca2+, myosin-mediated activation of the thin filament is greater in cardiac than in skeletal muscle, and this apparent cooperativity requires the presence of troponin C on thin filament regulatory strands.
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Affiliation(s)
- J M Metzger
- Department of Physiology, University of Michigan School of Medicine, Ann Arbor 48109, USA
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24
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Horiuti K, Kagawa K, Yamada K. Transient contraction of muscle fibers on photorelease of ATP at intermediate concentrations of Ca2+. Biophys J 1994; 67:1925-32. [PMID: 7858129 PMCID: PMC1225567 DOI: 10.1016/s0006-3495(94)80675-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We isometrically activated skinned fibers in rigor by flash photolysis of caged ATP at various [Ca2+] at 8 degrees C. On release of ATP, tension initially decreased with the same time course at all [Ca2+]. At high [Ca2+] (pCa < or = 5.8), tension rose to the steady-state plateau after the brief relaxation. When the [Ca2+] was intermediate (7.0 < or = pCa < or = 6.0), tension temporarily overshot the final steady-state level. The half-time during this tension transient was longer at higher [Ca2+]. The transient contractions could be simulated by a simple kinetic model: R + ATP-->Q, and X<-->Q<-->A, where R, X, and A are the rigor, relaxed, and active-tension states, respectively; Q is a "pre-active" state where tension is very low; and Ca2+ affects only the X-Q transition. This scheme was also useful for predicting the tension transients in Ca(2+)- and P(i)-jump experiments at various [Ca2+]. ADP enhanced the Ca2+ sensitivity of the ATP-induced transient contraction, which was not in the scope of the model.
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Affiliation(s)
- K Horiuti
- Department of Physiology, Oita Medical University, Japan
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25
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Abstract
A new molecular model is proposed for muscle contraction, that involves the electrical charging of the long (C-terminal) alpha-helical part of the head of the myosin molecule (S1) while the head is attached to actin; as it charges the alpha-helical part moves in the radial electric field between the filaments. The alpha-helical part snaps back when the myosin molecule is discharged electrically, at the moment that ATP binds to the active enzymatic site. This snap-back model explains several puzzling phenomena in contractility, as well as providing a physical explanation for the origin of an impulsive force that drives muscle contraction.
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26
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Lazzarino DA, Boldogh I, Smith MG, Rosand J, Pon LA. Yeast mitochondria contain ATP-sensitive, reversible actin-binding activity. Mol Biol Cell 1994; 5:807-18. [PMID: 7812049 PMCID: PMC301098 DOI: 10.1091/mbc.5.7.807] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Sedimentation assays were used to demonstrate and characterize binding of isolated yeast mitochondria to phalloidin-stabilized yeast F-actin. These actin-mitochondrial interactions are ATP sensitive, saturable, reversible, and do not depend upon mitochondrial membrane potential. Protease digestion of mitochondrial outer membrane proteins or saturation of myosin-binding sites on F-actin with the S1 subfragment of skeletal myosin block binding. These observations indicate that a protein (or proteins) on the mitochondrial surface mediates ATP-sensitive, reversible binding of mitochondria to the lateral surface of microfilaments. Actin copurifies with mitochondria during subcellular fractionation and is released from the organelle upon treatment with ATP. Thus, actin-mitochondrial interactions resembling those observed in vitro may also exist in intact yeast cells. Finally, a yeast mutant bearing a temperature-sensitive mutation in the actin-encoding ACT1 gene (act1-3) displays temperature-dependent defects in transfer of mitochondria from mother cells to newly developed buds during yeast cell mitosis.
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Affiliation(s)
- D A Lazzarino
- Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, New York, New York 10032
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27
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Ventura-Clapier R, Veksler V. Myocardial ischemic contracture. Metabolites affect rigor tension development and stiffness. Circ Res 1994; 74:920-9. [PMID: 8156639 DOI: 10.1161/01.res.74.5.920] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Myocardial ischemia is characterized by a decrease in phosphocreatine (PCr) and Mg(2+)-ATP contents as well as an accumulation of myosin ATPase reaction products (inorganic phosphate [P(i)], protons, and Mg(2+)-ADP). The possibility that these metabolites play a role in rigor tension development was checked in rat ventricular Triton X-100-skinned fibers. Rigor tension was induced by stepwise decreasing [Mg(2+)-ATP] in the presence or in the absence of 12 mmol/L PCr. To mimic the diastolic ionic environment of the myofibrils, [free Ca2+] was set at 100 nmol/L (pCa 7); [free Mg2+], at 1 mmol/L; and ionic strength, at 160 mmol/L. In control conditions (pH 7.1, with no added P(i) or Mg(2+)-ADP), the pMg(2+)-ATP for half-maximal rigor tension (pMg(2+)-ATP50) was 5.07 +/- 0.03 in the presence of PCr. After withdrawal of PCr, the pMg2+)-ATP50 value was shifted toward higher Mg(2+)-ATP values (3.57 +/- 0.03). Addition of 20 mmol/L P(i) shifted the pMg(2+)-ATP50 to 3.71 +/- 0.04 (P < .05) in the absence of PCr and in the opposite direction to 4.98 +/- 0.02 (P < .01) in the presence of PCr. Acidic pH (6.6) strongly increased pMg(2+)-ATP50 in both the absence (3.90 +/- 0.03, P < .001) and presence (5.44 +/- 0.02, P < .001) of PCr. Conversely, Mg(2+)-ADP (250 mumol/L) decreased pMg(2+)-ATP50 to 3.26 +/- 0.06 (P < .001) in the absence of PCr; at pMg(2+)-ATP 4, no rigor tension was observed until PCr concentration was decreased to < 2 mmol/L. At acidic pH, maximal rigor tension was lower by 29% compared with control conditions, whereas in the presence of Mg(2+)-ADP, maximal rigor tension developed to 143% of the control value; P(i) had no effect. The tension-to-stiffness (measured by the quick length-change technique) ratio was lower in rigor (no PCr and pMg(2+)-ATP 6) than during Ca2+ activation in the presence of both PCr and ATP. Compared with control rigor conditions, this parameter was unchanged by Mg(2+)-ADP and decreased by acidic pH, suggesting a proton-induced decrease in the amount of force per crossbridge. In addition to their known effects on active tension, Mg(2+)-ADP and protons affect rigor tension and influence ischemic contracture development. It is concluded that ischemic contracture and increased myocardial stiffness may be mediated by a decreased PCr and local Mg(2+)-ADP accumulation. This emphasizes the importance of myofibrillar creatine kinase activity in preventing ischemic contracture.
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Affiliation(s)
- R Ventura-Clapier
- Cardiologie Cellulaire et Moléculaire, CJF INSERM 92-11, Université Paris-Sud, Faculté de Pharmacie, Châtenay-Malabry, France
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28
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Ventura-Clapier R, Veksler V, Hoerter JA. Myofibrillar creatine kinase and cardiac contraction. Mol Cell Biochem 1994; 133-134:125-44. [PMID: 7808450 DOI: 10.1007/bf01267952] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
This article is a review on the organization and function of myofibrillar creatine kinase in striated muscle. The first part describes myofibrillar creatine kinase as an integral structural part of the complex organization of myofibrils in striated muscle. The second part considers the intrinsic biochemical and mechanical properties of myofibrils and the functional coupling between myofibrillar CK and myosin ATPase. Skinned fiber studies have been developed to evidence this functional coupling and the consequences for cardiac contraction. The data show that creatine kinase in myofibrils is effective enough to sustain normal tension and relaxation, normal Ca sensitivity and kinetic characteristics. Moreover, the results suggest that myofibrillar creatine kinase is essential in maintaining adequate ATP/ADP ratio in the vicinity of myosin ATPase active site to prevent dysfunctioning of this enzyme. Implications for the physiology and physiopathology of cardiac muscle are discussed.
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29
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Kawai M, Wray JS, Zhao Y. The effect of lattice spacing change on cross-bridge kinetics in chemically skinned rabbit psoas muscle fibers. I. Proportionality between the lattice spacing and the fiber width. Biophys J 1993; 64:187-96. [PMID: 7679296 PMCID: PMC1262316 DOI: 10.1016/s0006-3495(93)81356-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Chemically skinned rabbit psoas muscle fibers/bundles were osmotically compressed with a macromolecule dextran T-500 (0-16%, g/100 ml) at 20 degrees C, 200 mM ionic strength, and pH 7.0. The lattice spacing of psoas bundles was measured by equatorial x-ray diffraction studies during relaxation and after rigor induction, and the results were compared with the fiber width measurements by optical microscopy. The purpose of the present study is to determine whether fiber width is a reliable measure of the lattice spacing, and to determine the available spacing for myosin cross-bridges between the thick and thin filaments. We observed that both the lattice spacing and the fiber width decreased with an increase in the dextran concentration during relaxation or after rigor induction, and that the spacing and the fiber width were proportionately related. We further observed that, in the absence of dextran, the lattice spacing (and the fiber width) shrank on a relax-to-rigor transition, whereas in the presence of 16% dextran, the spacing expanded on a relax-to-rigor transition. The cross-over of these plots occurred at the 4-7% dextran concentration. During Ca activation, the fiber width shrank in the absence of dextran, and it slightly expanded in the presence of 14.4% dextran. The degree of expansion was not as large as in the relax-to-rigor transition, and the cross-over occurred at about 11% dextran concentration. We also carried out experiments with dextran T-40 and T-10 to determine the upper limit of the molecular weight that enters the lattice space. We found that the upper limit is about 20 kD.
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Affiliation(s)
- M Kawai
- Department of Anatomy, University of Iowa, College of Medicine, Iowa City 52242
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30
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Gordon AM, Ridgway EB. Cross-bridges affect both TnC structure and calcium affinity in muscle fibers. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1993; 332:183-92; discussion 192-4. [PMID: 8109332 DOI: 10.1007/978-1-4615-2872-2_17] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In vertebrate striated muscle, calcium binding to troponin initiates contraction, a strong interaction of actin and myosin. In isolated proteins and skinned fibers, the strong interaction of myosin with actin also affects troponin. Fluorescent labels attached to troponin C show structural changes in the TnC environment with cross-bridge attachment and also with calcium binding. Evidence that this effect of crossbridges also occurs in intact striated muscle comes from studies in partially activated cardiac or skeletal muscle by others and in barnacle muscle by us. Length changes which detach myosin cross-bridges produce a brief burst of extra calcium that can be detected by aequorin in activated, voltage clamped single barnacle muscle fibers. That this calcium is coming from calcium bound to the activating site (troponin-C) is supported by several pieces of evidence. Studies on the dependence of the extra calcium on force and the time of the length change are consistent with the amplitude of the extra calcium being proportional to the bound calcium (CaTnC) and with increased cross-bridge attachment and force increasing calcium binding to troponin-C by up to a factor of 10. Importantly, stretch of active muscle (which first detaches cross-bridges and then enhances steady force) gives a biphasic response: first extra calcium (presumably due to cross-bridge detachment) and then, decreased calcium (presumably due to enhanced calcium binding to TnC). The enhanced calcium binding we see with elevated force (via strained cross-bridges) implies that calcium binding to TnC is enhanced not only be cross-bridge attachment but also by crossbridge (or thin filament) strain. This effect of cross-bridge attachment/force on calcium binding is consistent with a dual mechanism of calcium activation of contraction. First, calcium binds to troponin in the thin filament activating strong myosin binding to the thin filament. Then, strong myosin binding in turn provides additional activation either by increasing calcium binding or by changing the thin filament structure directly allowing additional cross-bridge attachment.
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Affiliation(s)
- A M Gordon
- Department of Physiology, University of Washington, Seattle 98195
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31
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Affiliation(s)
- A Romani
- Department of Physiology and Biophysics, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106-4970
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32
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Sakoda T, Horiuti K. Effects of ethylene glycol and calcium on the kinetics of contraction induced by photo-release of low concentrations of ATP in rat psoas muscle fibres. J Muscle Res Cell Motil 1992; 13:464-72. [PMID: 1401042 DOI: 10.1007/bf01738041] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
To induce isometric contraction in the absence of Ca2+ (10 mM EGTA), low concentrations (130 microM) of ATP were photoreleased from caged ATP in skinned fibres from rat psoas muscle at 15-16 degrees C. The magnitude of contraction was independent of the concentration of EGTA (1-30 mM). Each isometric transient (i) was paired with another (s) obtained under the same conditions but with 0.4% muscle stretch to elevate the rigor force before photolysis. The algebraic difference (d) between i and s was assumed to represent detachment of the crossbridges. The time course of force development (f) by the reattached crossbridges could be estimated by subtracting an appropriately scaled d from i (or s). Ethylene glycol (20% in solvent) reduced the magnitude and the rate of rise of f, although it scarcely affected d, suggesting that ethylene glycol inhibited reattachment of the crossbridges but not their detachment. The presence of Ca2+ (50 microM) increased the magnitude of f, but did not affect its time course (130 microM ATP). Detachment, d, was not influenced by Ca2+ in terms of both extent and rate. The effect of Ca2+ in the presence of ethylene glycol was indistinguishable from that in its absence. Ethylene glycol did not seem to substantially affect the extent of Ca-regulation on the contractile activity.
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Affiliation(s)
- T Sakoda
- Department of Physiology, Oita Medical University, Japan
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33
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Moss RL. Ca2+ regulation of mechanical properties of striated muscle. Mechanistic studies using extraction and replacement of regulatory proteins. Circ Res 1992; 70:865-84. [PMID: 1348975 DOI: 10.1161/01.res.70.5.865] [Citation(s) in RCA: 123] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Extraction of regulatory proteins from thick and thin filaments of vertebrate striated muscle has proven to be an important approach in elucidating roles of these proteins in regulating contraction and in probing specific mechanisms of activation. For some proteins, such as LC2 and C protein, extraction has been fundamental in demonstrating the importance of these proteins in modulating contraction and the kinetics of cross-bridge interaction. For other proteins, such as TnC and troponin, extraction has provided significant insight into the importance of thin-filament intermolecular cooperativity in modulating Ca2+ sensitivity of the contractile process. A combination of extraction and readdition has provided a means of introducing mutated or derivatized proteins into fibers to accomplish a variety of experimental objectives. The use of this approach is likely to grow with the need to test the functional consequences of site-specific mutations as part of studies directed to mechanisms of regulation or altered regulation in heart and skeletal muscles under normal and pathophysiological conditions. Such studies are likely to include extraction in combination with other probes of function such as flash photolysis of reaction substrates or products within the cross-bridge interaction cycle. Although extraction is a powerful approach and is likely to be extended to proteins not discussed in this review, an essential element of experimental design in studies such as these is that appropriate control experiments be done to verify that observed effects of the extraction protocol are specifically attributable to the protein that is removed.
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Affiliation(s)
- R L Moss
- Department of Physiology, University of Wisconsin School of Medicine, Madison 53706
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34
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Abstract
1. Responses of isolated rat lacrimal cells to local applications of ATP were studied using tight-seal whole-cell recording and/or Fura-2-derived calcium concentration measurements. 2. In cells where variations in Ca2+ concentration were prevented by use of a strong Ca2+ buffer, ATP was found to induce an inward current response at negative holding potentials. With 10 microM-ATP, the current amplitude ranged between 20 and 200 pA. The reversal potential of this ATP-induced current was close to 0 mV with normal external solution and shifted to -19 +/- 3 mV (mean +/- S.D.) when the concentration of external monovalent cations was halved. These results indicate that the channels have a cationic selectivity. The response amplitude decreased markedly from trial to trial, indicating a desensitization process which was irreversible on the time scale of the recordings. 3. Steady state I-V curves for the ATP-induced current in normal saline showed a marked inward rectification. This rectification appeared to be linked to a time-dependent activation of the channels, as hyperpolarizing voltage jumps elicited a time-dependent current increase. This relaxation could be fitted by a double-exponential function, with time constants (at -120 mV) of 0.9 +/- 0.3 ms and 110 +/- 6.4 ms. 4. Variance analysis of the ATP-induced current gave a single-channel current value of 0.34 pA at -60 mV. The single-channel current amplitude varied linearly with potential, with a slope close to 6 pS. The relation between noise covariance and time could be fitted by a double-exponential function, with time constants (at -60 mV) of 0.8 +/- 0.4 ms and 6.8 +/- 3.4 ms (mean +/- S.D.). 5. In an isotonic Ca2+ solution, 10 microM-ATP induced an inward current at -60 mV with a calculated single-channel current amplitude obtained from noise analysis close to 0.2 pA. In an external solution containing 10 mM-calcium and no sodium, 50 microM-ATP elicited a current with a reversal potential of -19 mV. 6. Fura-2 measurements were performed in intact cells or in cells dialysed with a low concentration of Ca2+ buffer (e.g. 0.5 mM-EGTA). Under such conditions ATP induced increases of the internal Ca2+ concentration with very variable amplitudes. In some cells Ca2+ rises of 50 nM or lower were found. Minimal activation of Ca(2+)-dependent channels was then observed. In other cells large Ca2+ rises (up to 500 nM) were observed and were then correlated with marked activation of Ca(2+)-dependent channels.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- P Vincent
- Laboratoire de Neurobiologie, Ecole Normale Supérieure, Paris, France
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35
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Tang JM, Wang J, Eisenberg RS. Studies on intact sarcoplasmic reticulum: patch clamp recording and tension measurement in lobster split muscle fibers. Methods Enzymol 1992; 207:692-9. [PMID: 1382208 DOI: 10.1016/0076-6879(92)07050-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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36
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Tsujimoto T. Effect of ryanodine on glycerinated rabbit psoas muscle fibers. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1992; 311:327-8. [PMID: 1529763 DOI: 10.1007/978-1-4615-3362-7_26] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- T Tsujimoto
- Department of Physiology, Wakayama Medical College, Japan
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37
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Hard R, Cypher C. Reactivation of newt lung cilia: evidence for a possible temperature- and MgATP-induced activation mechanism. CELL MOTILITY AND THE CYTOSKELETON 1992; 21:187-98. [PMID: 1581973 DOI: 10.1002/cm.970210303] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Optimal conditions have been developed for the isolation and reactivation of highly coupled, demembranated ciliary axonemes from newt lungs [Hard, Cypher, and Schabtach, 1988, Cell Motil. Cytoskeleton 10:271-284]. In the present study, the motility of these cilia was further characterized by examining the effects of nucleotides, divalent cations, and temperature on beat frequency. When exposed to a reactivating solution containing Mg2+ and ATP, nearly 100% of the axonemes were motile and beat at frequencies of 0-50 Hz, depending on [MgATP] and temperature. Divalent cations were required for movement, with Mg2+ 2-3 times more effective than Ca2+. There was no absolute requirement for Ca2+ for motility. The beat frequencies obtained with fixed ATP and varying Mg2+ concentrations indicate that MgATP serves as the actual substrate. The effects of MgATP on beat frequency depended on the degree of mechanochemical coupling and temperature. When highly coupled preparations were reactivated at 21 degrees C, double reciprocal plots of beat frequency vs. [MgATP] were biphasic with extrapolated Fmax values of 22 and 44.8 Hz. However, when reactivated at 10 degrees C and 30 degrees C, linear plots were generated with Fmax values of 18.3 and 48.9 Hz, respectively. The beat frequencies of cultured cells and reactivated axonemes also varied biphasically with temperature. Our data suggest that newt lung respiratory cilia possess an intra-axonemal activation mechanism involving a temperature- and MgATP-induced transition between two distinct states whose maximum beat frequencies differ by 200-300%.
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Affiliation(s)
- R Hard
- Department of Anatomical Sciences, SUNY, Buffalo 14214
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38
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Sakoda T, Horiuti K, Yamada K. Effects of calcium and ethylene glycol on force transients on photogeneration of low concentrations of ATP in skeletal muscle fibers. ACTA ACUST UNITED AC 1992. [DOI: 10.1016/s0021-5198(19)60012-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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39
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Swartz DR, Greaser ML, Marsh BB. Regulation of binding of subfragment 1 in isolated rigor myofibrils. J Cell Biol 1990; 111:2989-3001. [PMID: 2148565 PMCID: PMC2116422 DOI: 10.1083/jcb.111.6.2989] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
A steric-hindrance model has been used to explain the regulation of muscle contraction by tropomyosin-troponin complex. The regulation of binding was studied by microscopic observation of mixtures of fluorescent subfragment 1 (S1) with rigor myofibrils at different actin-to-S1 ratios and in the presence and absence of calcium. Procedures were adapted to protect the critical thiols of S1 before conjugation to thiol-specific fluorochromes, this giving fluorescent S1 with unaltered enzyme activity. S1 binding was greatest in the I band (except at the Z-lines) in the presence of calcium regardless of the [S1]. The patterns in the absence of calcium depended on the actin-to-S1 ratios: low [S1], binding in the myosin-actin overlap region; intermediate [S1], highest binding at the A-I junction; high [S1], greatest binding in the I-band. The two distinct binding patterns observed at low [S1] were demonstrated by dual-channel fluorescence microscopy when myofibrils were sequentially incubated with fluorescent S1 without calcium followed by a different fluorescent S1 with calcium. These observations support the concept of rigor activation of actin sites. The change in the pattern upon increasing [S1] without calcium demonstrate cooperative interactions along the thin filament. However, these interactions (under the conditions used without calcium) do not appear to extend over greater than 2-3 tropomyosin-troponin-7 actin functional units.
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Affiliation(s)
- D R Swartz
- University of Wisconsin, Muscle Biology Laboratory, Madison 53706
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40
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Millar NC, Homsher E. The effect of phosphate and calcium on force generation in glycerinated rabbit skeletal muscle fibers. A steady-state and transient kinetic study. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)30494-5] [Citation(s) in RCA: 195] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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41
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Brandt PW, Roemer D, Schachat FH. Co-operative activation of skeletal muscle thin filaments by rigor crossbridges. The effect of troponin C extraction. J Mol Biol 1990; 212:473-80. [PMID: 2325129 DOI: 10.1016/0022-2836(90)90326-h] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
When Ca2+ binds to troponin C (TnC), all 26 troponin-tropomyosin (Tn-Tm) complexes of a regulatory strand change in concert from the inactive to the active configuration. To see if the complexes respond similarly when they are activated by rigor crossbridges in the absence of Ca2+, we determined the slope (ns) of the bell-shaped pS/tension (pS = -log [MgATP], where S = MgATP2-) relationship between pS 5, where the tension is maximal, and pS 2.3, where fibers are fully relaxed. In control skinned rabbit psoas fibers the ns value is greater than 4; it progressively decreases with TnC extraction. This decrease in ns with TnC extraction is analogous to the decrease in the slope (Hill coefficient) of the pCa/tension (pCa = -log [Ca2+]) relationship with extraction. Complete TnC extraction reduces the maximum substrate-induced tension by only 25%; in contrast, it reduces the maximum Ca2+ induced tension to zero. The effects of TnC extraction on the slope of the pS/tension curve are explained by the assumptions that (1) extracted Tn-Tm complexes no longer change in concert with their neighbors but change independently of them, and (2) co-operative signals cannot cross extracted Tn-Tm complexes. The ns value, therefore, like the nH, is a direct function of the number of contiguous, intact, Tn-Tm complexes in a stretch of a regulatory strand. To describe qualitatively the bi-phasic pS/tension relationship, the mono-phasic pCa/tension relationship, and the effects of TnC extraction on them, we introduce a version of the concerted-transition formalism which includes two activating ligands, Ca2+ and rigor crossbridges.
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Affiliation(s)
- P W Brandt
- Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Colombia University, New York, NY 10032
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42
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Harrison SM, Bers DM. Temperature dependence of myofilament Ca sensitivity of rat, guinea pig, and frog ventricular muscle. THE AMERICAN JOURNAL OF PHYSIOLOGY 1990; 258:C274-81. [PMID: 2305870 DOI: 10.1152/ajpcell.1990.258.2.c274] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cooling the superfusate of intact ventricular muscle, from 30 degrees C to below 4 degrees C in less than 2 s, leads to contractures thought to reflect the amount of Ca available for release from the sarcoplasmic reticulum (SR). On rewarming, tension transiently increases in guinea pig and rat ventricular muscle. It has been proposed that this rewarming tension spike reflects changes in myofilament Ca sensitivity and maximum Ca-activated force (Cmax) associated with rewarming. There are differences in intracellular Ca regulation among cardiac muscle preparations. Some characteristics of rapid-cooling contractures (e.g., the magnitude of the rewarming spike) also differ between species. Therefore, the Ca sensitivity of skinned ventricular muscle from the rat, guinea pig, and frog was determined at 29 (22 degrees C for frog ventricular preparations), 8, and 1 degrees C. The results show that cooling rat and guinea pig ventricular muscle from 29 to 1 degrees C shifts the pCa vs. tension relationship toward higher [Ca2+] by 0.65 and 0.55 pCa units, respectively. Cooling to 1 degrees C also reduced Cmax to 3.3 and 7.8% of that at 29 degrees C in rat and guinea pig ventricular muscle, respectively. Similar results were found for frog ventricular muscle, in which cooling from 22 to 1 degrees C reduced Ca sensitivity by 0.6 pCa units and Cmax to 45.7% of its value at 22 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S M Harrison
- Division of Biomedical Sciences, University of California, Riverside 92521
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43
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Bagni MA, Cecchi G, Schoenberg M. A model of force production that explains the lag between crossbridge attachment and force after electrical stimulation of striated muscle fibers. Biophys J 1988; 54:1105-14. [PMID: 3233267 PMCID: PMC1330421 DOI: 10.1016/s0006-3495(88)83046-7] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Whereas the mechanical behavior of fully activated fibers can be explained by assuming that attached force-producing crossbridges exist in at least two configurations, one exerting more force than the other (Huxley A. F., and R. M. Simmons. 1971. Nature [Lond.]. 233:533-538), and the behavior of relaxed fibers can be explained by assuming a single population of weakly binding rapid-equilibrium crossbridges (Schoenberg, M. 1988. Biophys. J. 54:135-148), it has not been possible to explain the transition between rest and activation in these terms. The difficulty in explaining why, after electrical stimulation of resting intact frog skeletal muscle fibers at 1-5 degrees C, force development lags stiffness development by more than 15 ms has led a number of investigators to postulate additional crossbridge states. However, postulation of an additional crossbridge state will not explain the following three observations: (a) Although the lag between force and stiffness is very different after stimulation, during the redevelopment of force after an extended period of high velocity shortening, and during relaxation of a tetanus, nonetheless, the plots of force versus stiffness in each of these cases are approximately the same. (b) When the lag between stiffness and force during the rising phase of a twitch is changed nearly fourfold by changing temperature, again the plot of force versus stiffness remains essentially unchanged. (c) When a muscle fiber is subjected to a small quick length change, the rate constant for the isometric force recovery is faster when the length change is applied during the rising phase of a tenanus than when it is applied on the plateau. We have been able to explain all the above findings using a model for force production that is similar to the 1971 model of Huxley and Simmons, but which makes the additional assumption that the force-producing transition envisioned by them is a cooperative one, with the back rate constant of the force-producing transition decreasing as more crossbridges attach.
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Affiliation(s)
- M A Bagni
- Dipartimento di Scienze Fisiologiche, Universita degli Studi, Firenze, Italy
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44
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Horiuti K, Higuchi H, Umazume Y, Konishi M, Okazaki O, Kurihara S. Mechanism of action of 2, 3-butanedione 2-monoxime on contraction of frog skeletal muscle fibres. J Muscle Res Cell Motil 1988; 9:156-64. [PMID: 2458382 DOI: 10.1007/bf01773737] [Citation(s) in RCA: 118] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The mechanism of the inhibitory effect of 2,3-butanedione 2-monoxime (BDM) on contraction of frog skeletal muscles was studied using skinned fibres and aequorin-injected intact fibres. The tension development of skinned fibres directly activated with calcium was strongly inhibited by BDM. This agent also had effects on the sarcoplasmic reticulum in the skinned preparations, suppressing the calcium pump function and enhancing the activity of the 'calcium-induced calcium release' mechanism. In electrically stimulated intact fibres, although BDM slightly suppressed the elevation of the intracellular calcium ion concentration, this effect was so weak that it would not explain the strong inhibitory effect of the agent on the tension development by the intact fibres. It was concluded that the tension reducing effect of BDM on intact fibres was due mainly to its direct action on the contractile system. The mode of this action of BDM was further examined with skinned fibres in view of its effects on the maximum shortening speed and isometric tension in low MgATP environments.
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Affiliation(s)
- K Horiuti
- Department of Physiology, Jikei University School of Medicine, Tokyo, Japan
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45
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Brozovich FV, Yates LD, Gordon AM. Muscle force and stiffness during activation and relaxation. Implications for the actomyosin ATPase. J Gen Physiol 1988; 91:399-420. [PMID: 2967885 PMCID: PMC2216139 DOI: 10.1085/jgp.91.3.399] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Isolated skinned frog skeletal muscle fibers were activated (increasing [Ca2+]) and then relaxed (decreasing [Ca2+]) with solution changes, and muscle force and stiffness were recorded during the steady state. To investigate the actomyosin cycle, the biochemical species were changed (lowering [MgATP] and elevating [H2PO4-]) to populate different states in the actomyosin ATPase cycle. In solutions with 200 microM [MgATP], compared with physiological [MgATP], the slope of the plot of relative steady state muscle force vs. stiffness was decreased. At low [MgATP], cross-bridge dissociation from actin should be reduced, increasing the population of the last cross-bridge state before dissociation. These data imply that the last cross-bridge state before dissociation could be an attached low-force-producing or non-force-producing state. In solutions with 10 mM total Pi, compared to normal levels of MgATP, the maximally activated muscle force was reduced more than muscle stiffness, and the slope of the plot of relative steady state muscle force vs. stiffness was reduced. Assuming that in elevated Pi, Pi release from the cross-bridge is reversed, the state(s) before Pi release would be populated. These data are consistent with the conclusion that the cross-bridges are strongly bound to actin before Pi release. In addition, if Ca2+ activates the ATPase by allowing for the strong attachment of the myosin to actin in an A.M.ADP.Pi state, it could do so before Pi release. The calcium sensitivity of muscle force and stiffness in solutions with 4 mM [MgATP] was bracketed by that measured in solutions with 200 microM [MgATP], where muscle force and stiffness were more sensitive to calcium, and 10 mM total Pi, where muscle force and stiffness were less sensitive to calcium. The changes in calcium sensitivity were explained using a model in which force-producing and rigor cross-bridges can affect Ca2+ binding or promote the attachment of other cross-bridges to alter calcium sensitivity.
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Affiliation(s)
- F V Brozovich
- Department of Physiology and Biophysics, University of Washington, Seattle 98195
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46
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Somlyo AV, Goldman YE, Fujimori T, Bond M, Trentham DR, Somlyo AP. Cross-bridge kinetics, cooperativity, and negatively strained cross-bridges in vertebrate smooth muscle. A laser-flash photolysis study. J Gen Physiol 1988; 91:165-92. [PMID: 3373178 PMCID: PMC2216129 DOI: 10.1085/jgp.91.2.165] [Citation(s) in RCA: 128] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The effects of laser-flash photolytic release of ATP from caged ATP [P3-1(2-nitrophenyl)ethyladenosine-5'-triphosphate] on stiffness and tension transients were studied in permeabilized guinea pig protal vein smooth muscle. During rigor, induced by removing ATP from the relaxed or contracting muscles, stiffness was greater than in relaxed muscle, and electron microscopy showed cross-bridges attached to actin filaments at an approximately 45 degree angle. In the absence of Ca2+, liberation of ATP (0.1-1 mM) into muscles in rigor caused relaxation, with kinetics indicating cooperative reattachment of some cross-bridges. Inorganic phosphate (Pi; 20 mM) accelerated relaxation. A rapid phase of force development, accompanied by a decline in stiffness and unaffected by 20 mM Pi, was observed upon liberation of ATP in muscles that were released by 0.5-1.0% just before the laser pulse. This force increment observed upon detachment suggests that the cross-bridges can bear a negative tension. The second-order rate constant for detachment of rigor cross-bridges by ATP, in the absence of Ca2+, was estimated to be 0.1-2.5 X 10(5) M-1s-1, which indicates that this reaction is too fast to limit the rate of ATP hydrolysis during physiological contractions. In the presence of Ca2+, force development occurred at a rate (0.4 s-1) similar to that of intact, electrically stimulated tissue. The rate of force development was an order of magnitude faster in muscles that had been thiophosphorylated with ATP gamma S before the photochemical liberation of ATP, which indicates that under physiological conditions, in non-thiophosphorylated muscles, light-chain phosphorylation, rather than intrinsic properties of the actomyosin cross-bridges, limits the rate of force development. The release of micromolar ATP or CTP from caged ATP or caged CTP caused force development of up to 40% of maximal active tension in the absence of Ca2+, consistent with cooperative attachment of cross-bridges. Cooperative reattachment of dephosphorylated cross-bridges may contribute to force maintenance at low energy cost and low cross-bridge cycling rates in smooth muscle.
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Affiliation(s)
- A V Somlyo
- Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia 19104
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47
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Fabiato A. Computer programs for calculating total from specified free or free from specified total ionic concentrations in aqueous solutions containing multiple metals and ligands. Methods Enzymol 1988; 157:378-417. [PMID: 3231093 DOI: 10.1016/0076-6879(88)57093-3] [Citation(s) in RCA: 829] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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48
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Schachat FH, Diamond MS, Brandt PW. Effect of different troponin T-tropomyosin combinations on thin filament activation. J Mol Biol 1987; 198:551-4. [PMID: 3430619 DOI: 10.1016/0022-2836(87)90300-7] [Citation(s) in RCA: 137] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The response of permeabilized rabbit fast skeletal muscle fibers to calcium is determined by the troponin T (TnT) and tropomyosin (Tm) isoforms they express. Fibers expressing primarily TnT2f and alpha 2 Tm exhibit steeper pCa/tension relations than those in which either TnT1f or TnT3f and alpha beta Tm predominate. Troponin C extraction studies show that lower slopes do not result from a less concerted transition on the thin filament: the Tn-Tm regulatory strand activates as a unit in all fast fibers. Because the TnT variants differ in their N-terminal segments, and this region overlaps adjacent Tms on the regulatory strand, we propose that both the end-to-end overlap of Tm and the effect of TnT on that interaction are the basis of the concerted transition of the regulatory strand to the active state that occurs in the presence of calcium. Moreover, the effect of different Tn-Tm combinations on the ratio of the affinities of TnC for calcium in the relaxed and active states appears to be a significant determinant of the contractile properties of fast fibers in vivo.
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Affiliation(s)
- F H Schachat
- Department of Anatomy, Duke University Medical Center, Durham, NC 27710
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49
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Brandt PW, Diamond MS, Rutchik JS, Schachat FH. Co-operative interactions between troponin-tropomyosin units extend the length of the thin filament in skeletal muscle. J Mol Biol 1987; 195:885-96. [PMID: 3656437 DOI: 10.1016/0022-2836(87)90492-x] [Citation(s) in RCA: 98] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Ca2+ binding to troponin C (TnC), a subunit of the thin filament regulatory strand, activates vertebrate skeletal muscle contraction. Tension, however, increases with Ca2+ too abruptly to be the result of binding to sites on individual TnCs. Because extraction of one TnC on average per regulatory strand dramatically reduces the slope of the tension/Ca2+ relationship, we proposed that all 26 troponin-tropomyosin complexes of the regulatory strand form a co-operative system. This study of permeabilized (chemically skinned) rabbit psoas fibers analyzes the extraction time-course, the distribution of extraction sites on regulatory strands and the effects of extraction on the co-operativity of the tension/Ca2+ relationship. Two components of TnC are resolved in the time-course of extraction: a "rapidly extracting" component that can be selectively removed without affecting tension or co-operativity, and a "slow extracting" component whose loss reduces tension and co-operativity. Extraction of [14C]TnC shows that the slowly extracting component is lost randomly, so that, after removal of 5% of the TnC, most extracted strands have lost one TnC. Extraction interrupts the transmission of co-operativity by dividing the regulatory strand into smaller, independent co-operative systems; it reduces tension by preventing Ca2+ activation of TnC-depleted regulatory units. Co-operativity of the tension/Ca2+ relationship is modeled with the concerted-transition formalism for intact systems of 26 regulatory units, and for the smaller systems in extracted fibers.
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Affiliation(s)
- P W Brandt
- Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, NY 10032
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50
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Greene LE, Williams DL, Eisenberg E. Regulation of actomyosin ATPase activity by troponin-tropomyosin: effect of the binding of the myosin subfragment 1 (S-1).ATP complex. Proc Natl Acad Sci U S A 1987; 84:3102-6. [PMID: 2953023 PMCID: PMC304816 DOI: 10.1073/pnas.84.10.3102] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
In our model of regulation, the observed lack of cooperativity in the binding of myosin subfragment 1 (S-1) with bound ATP to the troponin-tropomyosin-actin complex (regulated actin) is explained by S-1.ATP having about the same affinity for the conformation of the regulated actin that activates the myosin ATPase activity (turned-on form) and the conformation that does not activate the myosin ATPase activity (turned-off form). This predicts that, in the absence of Ca2+, S-1.ATP should not turn on the regulated actin filament. In the present study, we tested this prediction by using either unmodified S-1 or S-1 chemically modified with N,N'-p-phenylenedimaleimide (pPDM X S-1) so that functionally it acts like S-1.ATP, although it does not hydrolyze ATP. We found that, in the absence of Ca2+, neither S-1.ATP nor pPDM X S-1.ATP significantly turns on the ATPase activity of the regulated complex of actin and S-1 (acto X S-1). In contrast, in the presence of Ca2+, pPDM X S-1.ATP binding almost completely turns on the regulated acto.S-1 ATPase activity. These results can be explained by our original cooperativity model, with pPDM X S-1.ATP binding only approximately equal to 2-fold more strongly to the turned-on form than to the turned-off form of regulated actin. However, our results are not consistent with our alternative model, which predicts that if pPDM X S-1.ATP binds to actin in the absence of Ca2+ but does not turn on the ATPase activity, then it should also not turn on the ATPase activity in the presence of Ca2+.
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