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Awinda PO, Vander Top BJ, Turner KL, Tanner BCW. Danicamtiv affected isometric force and cross-bridge kinetics similarly in skinned myocardial strips from male and female rats. J Muscle Res Cell Motil 2024; 45:115-122. [PMID: 38717549 DOI: 10.1007/s10974-024-09669-5] [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: 12/20/2023] [Accepted: 03/19/2024] [Indexed: 08/11/2024]
Abstract
Myotropes are pharmaceuticals that have recently been developed or are under investigation for the treatment of heart diseases. Myotropes have had varied success in clinical trials. Initial research into myotropes have widely focused on animal models of cardiac dysfunction in comparison with normal animal cardiac physiology-primarily using males. In this study we examined the effect of danicamtiv, which is one type of myotrope within the class of myosin activators, on contractile function in permeabilized (skinned) myocardial strips from male and female Sprague-Dawley rats. We found that danicamtiv increased steady-state isometric force production at sub-maximal calcium levels, leading to greater Ca2+-sensitivity of contraction for both sexes. Danicamtiv did not affect maximal Ca2+-activated force for either sex. Sinusoidal length-perturbation analysis was used to assess viscoelastic myocardial stiffness and cross-bridge cycling kinetics. Data from these measurements did not vary with sex, and the data suggest that danicamtiv slows cross-bridge cycling kinetics. These findings imply that danicamtiv increases force production via increasing cross-bridge contributions to activation of contraction, especially at sub-maximal Ca2+-activation. The inclusion of both sexes in animal models during the formative stages of drug development could be helpful for understanding the efficacy or limitation of a drug's therapeutic impact on cardiac function.
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Affiliation(s)
- Peter O Awinda
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA, 99164, USA
| | - Blake J Vander Top
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA, 99164, USA
| | - Kyrah L Turner
- School of Molecular Biosciences, Washington State University, Pullman, WA, 99164, USA
| | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA, 99164, USA.
- Department of Integrative Physiology and Neuroscience, Washington State University, Room 255 Vet/Biomed Research Building, 1815 Ferdinand's Lane, Pullman, WA, 99164-7620, USA.
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2
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Garg A, Lavine KJ, Greenberg MJ. Assessing Cardiac Contractility From Single Molecules to Whole Hearts. JACC Basic Transl Sci 2024; 9:414-439. [PMID: 38559627 PMCID: PMC10978360 DOI: 10.1016/j.jacbts.2023.07.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Revised: 07/14/2023] [Accepted: 07/14/2023] [Indexed: 04/04/2024]
Abstract
Fundamentally, the heart needs to generate sufficient force and power output to dynamically meet the needs of the body. Cardiomyocytes contain specialized structures referred to as sarcomeres that power and regulate contraction. Disruption of sarcomeric function or regulation impairs contractility and leads to cardiomyopathies and heart failure. Basic, translational, and clinical studies have adapted numerous methods to assess cardiac contraction in a variety of pathophysiological contexts. These tools measure aspects of cardiac contraction at different scales ranging from single molecules to whole organisms. Moreover, these studies have revealed new pathogenic mechanisms of heart disease leading to the development of novel therapies targeting contractility. In this review, the authors explore the breadth of tools available for studying cardiac contractile function across scales, discuss their strengths and limitations, highlight new insights into cardiac physiology and pathophysiology, and describe how these insights can be harnessed for therapeutic candidate development and translational.
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Affiliation(s)
- Ankit Garg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri, USA
- Center for Cardiovascular Research, Division of Cardiology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Kory J. Lavine
- Center for Cardiovascular Research, Division of Cardiology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Michael J. Greenberg
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri, USA
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3
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Kooiker KB, Mohran S, Turner KL, Ma W, Martinson A, Flint G, Qi L, Gao C, Zheng Y, McMillen TS, Mandrycky C, Mahoney-Schaefer M, Freeman JC, Costales Arenas EG, Tu AY, Irving TC, Geeves MA, Tanner BC, Regnier M, Davis J, Moussavi-Harami F. Danicamtiv Increases Myosin Recruitment and Alters Cross-Bridge Cycling in Cardiac Muscle. Circ Res 2023; 133:430-443. [PMID: 37470183 PMCID: PMC10434831 DOI: 10.1161/circresaha.123.322629] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2023] [Revised: 07/10/2023] [Accepted: 07/13/2023] [Indexed: 07/21/2023]
Abstract
BACKGROUND Modulating myosin function is a novel therapeutic approach in patients with cardiomyopathy. Danicamtiv is a novel myosin activator with promising preclinical data that is currently in clinical trials. While it is known that danicamtiv increases force and cardiomyocyte contractility without affecting calcium levels, detailed mechanistic studies regarding its mode of action are lacking. METHODS Permeabilized porcine cardiac tissue and myofibrils were used for X-ray diffraction and mechanical measurements. A mouse model of genetic dilated cardiomyopathy was used to evaluate the ability of danicamtiv to correct the contractile deficit. RESULTS Danicamtiv increased force and calcium sensitivity via increasing the number of myosins in the ON state and slowing cross-bridge turnover. Our detailed analysis showed that inhibition of ADP release results in decreased cross-bridge turnover with cross bridges staying attached longer and prolonging myofibril relaxation. Danicamtiv corrected decreased calcium sensitivity in demembranated tissue, abnormal twitch magnitude and kinetics in intact cardiac tissue, and reduced ejection fraction in the whole organ. CONCLUSIONS As demonstrated by the detailed studies of Danicamtiv, increasing myosin recruitment and altering cross-bridge cycling are 2 mechanisms to increase force and calcium sensitivity in cardiac muscle. Myosin activators such as Danicamtiv can treat the causative hypocontractile phenotype in genetic dilated cardiomyopathy.
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Affiliation(s)
- Kristina B. Kooiker
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
| | - Saffie Mohran
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Kyrah L. Turner
- School of Molecular Biosciences, Washington State University (K.L.T.)
| | - Weikang Ma
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Amy Martinson
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Galina Flint
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Lin Qi
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Chengqian Gao
- College of Basic Medical Sciences, Dalian Medical University, Liaoning, China (C.G., Y.Z.)
| | - Yahan Zheng
- College of Basic Medical Sciences, Dalian Medical University, Liaoning, China (C.G., Y.Z.)
| | - Timothy S. McMillen
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Anesthesiology and Pain Medicine (T.S.M.), University of Washington
| | - Christian Mandrycky
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Max Mahoney-Schaefer
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
| | - Jeremy C. Freeman
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
| | | | - An-Yu Tu
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Thomas C. Irving
- Department of Biology, Illinois Institute of Technology, Chicago (W.M., L.Q., T.C.I.)
| | - Michael A. Geeves
- School of Biosciences, Division of Natural Sciences, University of Kent, Canterbury, United Kingdom (M.A.G.)
| | - Bertrand C.W. Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University (B.C.W.T.)
| | - Michael Regnier
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Jennifer Davis
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Department of Bioengineering (S.M., A.M., G.F., C.M., A.-Y.T., M.R., J.D.), University of Washington
| | - Farid Moussavi-Harami
- Division of Cardiology, Medicine (K.B.K., M.M.-S., J.C.F., E.G.C.A., F.M.-H.), University of Washington
- Center of Translational Muscle Research (K.B.K., S.M., G.F., T.S.M., C.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
- Center for Cardiovascular Biology (K.B.K., A.M., M.R., J.D., F.M.-H.), University of Washington
- Department of Laboratory Medicine and Pathology (A.M., J.D., F.M.-H.), University of Washington
- Institute for Stem Cell & Regenerative Medicine (K.B.K., S.M., A.M., T.S.M., A.-Y.T., M.R., J.D., F.M.-H.), University of Washington
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4
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Schick BM, Dlugas H, Czeiszperger TL, Matus AR, Bukowski MJ, Chung CS. Reduced preload increases Mechanical Control (strain-rate dependence) of Relaxation by modifying myosin kinetics. Arch Biochem Biophys 2021; 707:108909. [PMID: 34015323 PMCID: PMC8635462 DOI: 10.1016/j.abb.2021.108909] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Revised: 04/09/2021] [Accepted: 04/30/2021] [Indexed: 12/16/2022]
Abstract
Rapid myocardial relaxation is essential in maintaining cardiac output, and impaired relaxation is an early indicator of diastolic dysfunction. While the biochemical modifiers of relaxation are well known to include calcium handling, thin filament activation, and myosin kinetics, biophysical and biomechanical modifiers can also alter relaxation. We have previously shown that the relaxation rate is increased by an increasing strain rate, not a reduction in afterload. The slope of the relaxation rate to strain rate relationship defines Mechanical Control of Relaxation (MCR). To investigate MCR further, we performed in vitro experiments and computational modeling of preload-adjustment using intact rat cardiac trabeculae. Trabeculae studies are often performed using isometric (fixed-end) muscles at optimal length (Lo, length producing maximal developed force). We determined that reducing muscle length from Lo increased MCR by 20%, meaning that reducing preload could substantially increase the sensitivity of the relaxation rate to the strain rate. We subsequently used computational modeling to predict mechanisms that might underlie this preload-dependence. Computational modeling was not able to fully replicate experimental data, but suggested that thin-filament properties are not sufficient to explain preload-dependence of MCR because the model required the thin-filament to become more activated at reduced preloads. The models suggested that myosin kinetics may underlie the increase in MCR at reduced preload, an effect that can be enhanced by force-dependence. Relaxation can be modified and enhanced by reduced preload. Computational modeling implicates myosin-based targets for treatment of diastolic dysfunction, but further model refinements are needed to fully replicate experimental data.
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Affiliation(s)
- Brianna M Schick
- Department of Physiology, Wayne State University, Detroit, MI, USA
| | - Hunter Dlugas
- Department of Physiology, Wayne State University, Detroit, MI, USA
| | | | | | | | - Charles S Chung
- Department of Physiology, Wayne State University, Detroit, MI, USA.
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5
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Fenwick AJ, Lin DC, Tanner BCW. Myosin cross-bridge kinetics slow at longer muscle lengths during isometric contractions in intact soleus from mice. Proc Biol Sci 2021; 288:20202895. [PMID: 33975478 DOI: 10.1098/rspb.2020.2895] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Muscle contraction results from force-generating cross-bridge interactions between myosin and actin. Cross-bridge cycling kinetics underlie fundamental contractile properties, such as active force production and energy utilization. Factors that influence cross-bridge kinetics at the molecular level propagate through the sarcomeres, cells and tissue to modulate whole-muscle function. Conversely, movement and changes in the muscle length can influence cross-bridge kinetics on the molecular level. Reduced, single-molecule and single-fibre experiments have shown that increasing the strain on cross-bridges may slow their cycling rate and prolong their attachment duration. However, whether these strain-dependent cycling mechanisms persist in the intact muscle tissue, which encompasses more complex organization and passive elements, remains unclear. To investigate this multi-scale relationship, we adapted traditional step-stretch protocols for use with mouse soleus muscle during isometric tetanic contractions, enabling novel estimates of length-dependent cross-bridge kinetics in the intact skeletal muscle. Compared to rates at the optimal muscle length (Lo), we found that cross-bridge detachment rates increased by approximately 20% at 90% of Lo (shorter) and decreased by approximately 20% at 110% of Lo (longer). These data indicate that cross-bridge kinetics vary with whole-muscle length during intact, isometric contraction, which could intrinsically modulate force generation and energetics, and suggests a multi-scale feedback pathway between whole-muscle function and cross-bridge activity.
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Affiliation(s)
- Axel J Fenwick
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA.,Washington Center for Muscle Biology, Washington State University, Pullman, WA 99164, USA
| | - David C Lin
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA.,Washington Center for Muscle Biology, Washington State University, Pullman, WA 99164, USA.,The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA.,Washington Center for Muscle Biology, Washington State University, Pullman, WA 99164, USA
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6
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Awinda PO, Watanabe M, Bishaw Y, Huckabee AM, Agonias KB, Kazmierczak K, Szczesna-Cordary D, Tanner BCW. Mavacamten decreases maximal force and Ca 2+ sensitivity in the N47K-myosin regulatory light chain mouse model of hypertrophic cardiomyopathy. Am J Physiol Heart Circ Physiol 2021; 320:H881-H890. [PMID: 33337957 PMCID: PMC8082789 DOI: 10.1152/ajpheart.00345.2020] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Revised: 12/10/2020] [Accepted: 12/10/2020] [Indexed: 01/12/2023]
Abstract
Morbidity and mortality associated with heart disease is a growing threat to the global population, and novel therapies are needed. Mavacamten (formerly called MYK-461) is a small molecule that binds to cardiac myosin and inhibits myosin ATPase. Mavacamten is currently in clinical trials for the treatment of obstructive hypertrophic cardiomyopathy (HCM), and it may provide benefits for treating other forms of heart disease. We investigated the effect of mavacamten on cardiac muscle contraction in two transgenic mouse lines expressing the human isoform of cardiac myosin regulatory light chain (RLC) in their hearts. Control mice expressed wild-type RLC (WT-RLC), and HCM mice expressed the N47K RLC mutation. In the absence of mavacamten, skinned papillary muscle strips from WT-RLC mice produced greater isometric force than strips from N47K mice. Adding 0.3 µM mavacamten decreased maximal isometric force and reduced Ca2+ sensitivity of contraction for both genotypes, but this reduction in pCa50 was nearly twice as large for WT-RLC versus N47K. We also used stochastic length-perturbation analysis to characterize cross-bridge kinetics. The cross-bridge detachment rate was measured as a function of [MgATP] to determine the effect of mavacamten on myosin nucleotide handling rates. Mavacamten increased the MgADP release and MgATP binding rates for both genotypes, thereby contributing to faster cross-bridge detachment, which could speed up myocardial relaxation during diastole. Our data suggest that mavacamten reduces isometric tension and Ca2+ sensitivity of contraction via decreased strong cross-bridge binding. Mavacamten may become a useful therapy for patients with heart disease, including some forms of HCM.NEW & NOTEWORTHY Mavacamten is a pharmaceutical that binds to myosin, and it is under investigation as a therapy for some forms of heart disease. We show that mavacamten reduces isometric tension and Ca2+ sensitivity of contraction in skinned myocardial strips from a mouse model of hypertrophic cardiomyopathy that expresses the N47K mutation in cardiac myosin regulatory light chain. Mavacamten reduces contractility by decreasing strong cross-bridge binding, partially due to faster cross-bridge nucleotide handling rates that speed up myosin detachment.
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Affiliation(s)
- Peter O Awinda
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Marissa Watanabe
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Yemeserach Bishaw
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Anna M Huckabee
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Keinan B Agonias
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
| | - Katarzyna Kazmierczak
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida
| | - Danuta Szczesna-Cordary
- Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, Florida
| | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
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7
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Fenwick AJ, Awinda PO, Yarbrough-Jones JA, Eldridge JA, Rodgers BD, Tanner BCW. Demembranated skeletal and cardiac fibers produce less force with altered cross-bridge kinetics in a mouse model for limb-girdle muscular dystrophy 2i. Am J Physiol Cell Physiol 2019; 317:C226-C234. [PMID: 31091146 DOI: 10.1152/ajpcell.00524.2018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Limb-girdle muscular dystrophy 2i (LGMD2i) is a dystroglycanopathy that compromises myofiber integrity and primarily reduces power output in limb muscles but can influence cardiac muscle as well. Previous studies of LGMD2i made use of a transgenic mouse model in which a proline-to-leucine (P448L) mutation in fukutin-related protein severely reduces glycosylation of α-dystroglycan. Muscle function is compromised in P448L mice in a manner similar to human patients with LGMD2i. In situ studies reported lower maximal twitch force and depressed force-velocity curves in medial gastrocnemius (MG) muscles from male P448L mice. Here, we measured Ca2+-activated force generation and cross-bridge kinetics in both demembranated MG fibers and papillary muscle strips from P448L mice. Maximal activated tension was 37% lower in MG fibers and 18% lower in papillary strips from P448L mice than controls. We also found slightly faster rates of cross-bridge recruitment and detachment in MG fibers from P448L than control mice. These increases in skeletal cross-bridge cycling could reduce the unitary force output from individual cross bridges by lowering the ratio of time spent in a force-bearing state to total cycle time. This suggests that the decreased force production in LGMD2i may be due (at least in part) to altered cross-bridge kinetics. This finding is notable, as the majority of studies germane to muscular dystrophies have focused on sarcolemma or whole muscle properties, whereas our findings suggest that the disease pathology is also influenced by potential downstream effects on cross-bridge behavior.
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Affiliation(s)
- Axel J Fenwick
- Department of Integrative Physiology and Neuroscience, Washington State University , Pullman, Washington.,Washington Center for Muscle Biology, Washington State University , Pullman, Washington
| | - Peter O Awinda
- Department of Integrative Physiology and Neuroscience, Washington State University , Pullman, Washington.,Washington Center for Muscle Biology, Washington State University , Pullman, Washington
| | - Jacob A Yarbrough-Jones
- Department of Integrative Physiology and Neuroscience, Washington State University , Pullman, Washington.,Washington Center for Muscle Biology, Washington State University , Pullman, Washington
| | - Jennifer A Eldridge
- Department of Integrative Physiology and Neuroscience, Washington State University , Pullman, Washington.,Washington Center for Muscle Biology, Washington State University , Pullman, Washington
| | - Buel D Rodgers
- Washington Center for Muscle Biology, Washington State University , Pullman, Washington.,AAVogen, Inc. , Rockville, Maryland
| | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University , Pullman, Washington.,Washington Center for Muscle Biology, Washington State University , Pullman, Washington
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8
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Kieu TT, Awinda PO, Tanner BCW. Omecamtiv Mecarbil Slows Myosin Kinetics in Skinned Rat Myocardium at Physiological Temperature. Biophys J 2019; 116:2149-2160. [PMID: 31103235 DOI: 10.1016/j.bpj.2019.04.020] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 04/10/2019] [Accepted: 04/15/2019] [Indexed: 12/15/2022] Open
Abstract
Heart failure is a life-threatening condition that occurs when the heart muscle becomes weakened and cannot adequately circulate blood and nutrients around the body. Omecamtiv mecarbil (OM) is a compound that has been developed to treat systolic heart failure via targeting the cardiac myosin heavy chain to increase myocardial contractility. Biophysical and biochemical studies have found that OM increases calcium (Ca2+) sensitivity of contraction by prolonging the myosin working stroke and increasing the actin-myosin cross-bridge duty ratio. Most in vitro studies probing the effects of OM on cross-bridge kinetics and muscle force production have been conducted at subphysiological temperature, even though temperature plays a critical role in enzyme activity and cross-bridge function. Herein, we used skinned, ventricular papillary muscle strips from rats to investigate the effects of [OM] on Ca2+-activated force production, cross-bridge kinetics, and myocardial viscoelasticity at physiological temperature (37°C). We find that OM only increases myocardial contractility at submaximal Ca2+ activation levels and not maximal Ca2+ activation levels. As [OM] increased, the kinetic rate constants for cross-bridge recruitment and detachment slowed for both submaximal and maximal Ca2+-activated conditions. These findings support a mechanism by which OM increases cardiac contractility at physiological temperature via increasing cross-bridge contributions to thin-filament activation as cross-bridge kinetics slow and the duration of cross-bridge attachment increases. Thus, force only increases at submaximal Ca2+ activation due to cooperative recruitment of neighboring cross-bridges, because thin-filament activation is not already saturated. In contrast, OM does not increase myocardial force production for maximal Ca2+-activated conditions at physiological temperature because cooperative activation of thin filaments may already be saturated.
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Affiliation(s)
- Thinh T Kieu
- Department of Integrative Physiology and Neuroscience
| | | | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience; Washington Center for Muscle Biology, Washington State University, Pullman, Washington.
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9
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Breithaupt JJ, Pulcastro HC, Awinda PO, DeWitt DC, Tanner BCW. Regulatory light chain phosphorylation augments length-dependent contraction in PTU-treated rats. J Gen Physiol 2018; 151:66-76. [PMID: 30523115 PMCID: PMC6314387 DOI: 10.1085/jgp.201812158] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Accepted: 11/07/2018] [Indexed: 12/13/2022] Open
Abstract
Contraction of cardiac muscle is regulated by sarcomere length and proteins that comprise the sarcomeric filaments. Breithaupt et al. find that phosphorylation of myosin regulatory light chain augments length-dependent activation of contraction when β-cardiac myosin heavy chain predominates. Force production by actin–myosin cross-bridges in cardiac muscle is regulated by thin-filament proteins and sarcomere length (SL) throughout the heartbeat. Prior work has shown that myosin regulatory light chain (RLC), which binds to the neck of myosin heavy chain, increases cardiac contractility when phosphorylated. We recently showed that cross-bridge kinetics slow with increasing SLs, and that RLC phosphorylation amplifies this effect, using skinned rat myocardial strips predominantly composed of the faster α-cardiac myosin heavy chain isoform. In the present study, to assess how RLC phosphorylation influences length-dependent myosin function as myosin motor speed varies, we used a propylthiouracil (PTU) diet to induce >95% expression of the slower β-myosin heavy chain isoform in rat cardiac ventricles. We measured the effect of RLC phosphorylation on Ca2+-activated isometric contraction and myosin cross-bridge kinetics (via stochastic length perturbation analysis) in skinned rat papillary muscle strips at 1.9- and 2.2-µm SL. Maximum tension and Ca2+ sensitivity increased with SL, and RLC phosphorylation augmented this response at 2.2-µm SL. Subtle increases in viscoelastic myocardial stiffness occurred with RLC phosphorylation at 2.2-µm SL, but not at 1.9-µm SL, thereby suggesting that RLC phosphorylation increases β-myosin heavy chain binding or stiffness at longer SLs. The cross-bridge detachment rate slowed as SL increased, providing a potential mechanism for prolonged cross-bridge attachment to augment length-dependent activation of contraction at longer SLs. Length-dependent slowing of β-myosin heavy chain detachment rate was not affected by RLC phosphorylation. Together with our previous studies, these data suggest that both α- and β-myosin heavy chain isoforms show a length-dependent activation response and prolonged myosin attachment as SL increases in rat myocardial strips, and that RLC phosphorylation augments length-dependent activation at longer SLs. In comparing cardiac isoforms, however, we found that β-myosin heavy chain consistently showed greater length-dependent sensitivity than α-myosin heavy chain. Our work suggests that RLC phosphorylation is a vital contributor to the regulation of myocardial contractility in both cardiac myosin heavy chain isoforms.
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Affiliation(s)
- Jason J Breithaupt
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA
| | - Hannah C Pulcastro
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA
| | - Peter O Awinda
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA
| | - David C DeWitt
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA
| | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA
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10
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Mamidi R, Li J, Gresham KS, Verma S, Doh CY, Li A, Lal S, Dos Remedios CG, Stelzer JE. Dose-Dependent Effects of the Myosin Activator Omecamtiv Mecarbil on Cross-Bridge Behavior and Force Generation in Failing Human Myocardium. Circ Heart Fail 2017; 10:CIRCHEARTFAILURE.117.004257. [PMID: 29030372 DOI: 10.1161/circheartfailure.117.004257] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 09/12/2017] [Indexed: 01/10/2023]
Abstract
BACKGROUND Omecamtiv mecarbil (OM) enhances systolic function in vivo by directly binding the myosin cross-bridges (XBs) in the sarcomere. However, the mechanistic details governing OM-induced modulation of XB behavior in failing human myocardium are unclear. METHODS AND RESULTS The effects of OM on steady state and dynamic XB behavior were measured in chemically skinned myocardial preparations isolated from human donor and heart failure (HF) left ventricle. HF myocardium exhibited impaired contractile function as evidenced by reduced maximal force, magnitude of XB recruitment (Pdf), and a slowed rate of XB detachment (krel) at submaximal Ca2+ activations. Ca2+ sensitivity of force generation (pCa50) was higher in HF myocardium when compared with donor myocardium, both prior to and after OM incubations. OM incubation (0.5 and 1.0 μmol/L) enhanced force generation at submaximal Ca2+ activations in a dose-dependent manner. Notably, OM induced a slowing in krel with 1.0 μmol/L OM but not with 0.5 μmol/L OM in HF myocardium. Additionally, OM exerted other differential effects on XB behavior in HF myocardium as evidenced by a greater enhancement in Pdf and slowing in the time course of cooperative XB recruitment (Trec), which collectively prolonged achievement of peak force development (Tpk), compared with donor myocardium. CONCLUSIONS Our findings demonstrate that OM augments force generation but also prolongs the time course of XB transitions to force-bearing states in remodeled HF myocardium, which may extend the systolic ejection time in vivo. Optimal OM dosing is critical for eliciting enhanced systolic function without excessive prolongation of systolic ejection time, which may compromise diastolic filling.
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Affiliation(s)
- Ranganath Mamidi
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.)
| | - Jiayang Li
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.)
| | - Kenneth S Gresham
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.)
| | - Sujeet Verma
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.)
| | - Chang Yoon Doh
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.)
| | - Amy Li
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.)
| | - Sean Lal
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.)
| | - Cristobal G Dos Remedios
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.)
| | - Julian E Stelzer
- From the Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH (R.M., J.L., C.Y.D., J.E.S.); Center for Translational Medicine, Lewis Katz School of Medicine, Temple University, Philadelphia, PA (K.S.G); Department of Horticulture Sciences, IFAS, Gulf Coast Research and Education Center, University of Florida, Wimauma (S.V.); Sydney Heart Bank, Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Australia (A.L., S.L., C.G.d.R.).
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11
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Bohlooli Ghashghaee N, Tanner BCW, Dong WJ. Functional significance of C-terminal mobile domain of cardiac troponin I. Arch Biochem Biophys 2017; 634:38-46. [PMID: 28958680 DOI: 10.1016/j.abb.2017.09.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2017] [Revised: 09/08/2017] [Accepted: 09/24/2017] [Indexed: 01/22/2023]
Abstract
Ca2+-regulation of cardiac contractility is mediated through the troponin complex, which comprises three subunits: cTnC, cTnI, and cTnT. As intracellular [Ca2+] increases, cTnI reduces its binding interactions with actin to primarily interact with cTnC, thereby enabling contraction. A portion of this regulatory switching involves the mobile domain of cTnI (cTnI-MD), the role of which in muscle contractility is still elusive. To study the functional significance of cTnI-MD, we engineered two cTnI constructs in which the MD was truncated to various extents: cTnI(1-167) and cTnI(1-193). These truncations were exchanged for endogenous cTnI in skinned rat papillary muscle fibers, and their influence on Ca2+-activated contraction and cross-bridge cycling kinetics was assessed at short (1.9 μm) and long (2.2 μm) sarcomere lengths (SLs). Our results show that the cTnI(1-167) truncation diminished the SL-induced increase in Ca2+-sensitivity of contraction, but not the SL-dependent increase in maximal tension, suggesting an uncoupling between the thin and thick filament contributions to length dependent activation. Compared to cTnI(WT), both truncations displayed greater Ca2+-sensitivity and faster cross-bridge attachment rates at both SLs. Furthermore, cTnI(1-167) slowed MgADP release rate and enhanced cross-bridge binding. Our findings imply that cTnI-MD truncations affect the blocked-to closed-state transition(s) and destabilize the closed-state position of tropomyosin.
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Affiliation(s)
- Nazanin Bohlooli Ghashghaee
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Bertrand C W Tanner
- The Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA
| | - Wen-Ji Dong
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA; The Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164, USA.
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12
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Myosin MgADP Release Rate Decreases as Sarcomere Length Increases in Skinned Rat Soleus Muscle Fibers. Biophys J 2017; 111:2011-2023. [PMID: 27806282 DOI: 10.1016/j.bpj.2016.09.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Revised: 09/15/2016] [Accepted: 09/20/2016] [Indexed: 11/21/2022] Open
Abstract
Actin-myosin cross-bridges use chemical energy from MgATP hydrolysis to generate force and shortening in striated muscle. Previous studies show that increases in sarcomere length can reduce thick-to-thin filament spacing in skinned muscle fibers, thereby increasing force production at longer sarcomere lengths. However, it is unclear how changes in sarcomere length and lattice spacing affect cross-bridge kinetics at fundamental steps of the cross-bridge cycle, such as the MgADP release rate. We hypothesize that decreased lattice spacing, achieved through increased sarcomere length or osmotic compression of the fiber via dextran T-500, could slow MgADP release rate and increase cross-bridge attachment duration. To test this, we measured cross-bridge cycling and MgADP release rates in skinned soleus fibers using stochastic length-perturbation analysis at 2.5 and 2.0 μm sarcomere lengths as pCa and [MgATP] varied. In the absence of dextran, the force-pCa relationship showed greater Ca2+ sensitivity for 2.5 vs. 2.0 μm sarcomere length fibers (pCa50 = 5.68 ± 0.01 vs. 5.60 ± 0.01). When fibers were compressed with 4% dextran, the length-dependent increase in Ca2+ sensitivity of force was attenuated, though the Ca2+ sensitivity of the force-pCa relationship at both sarcomere lengths was greater with osmotic compression via 4% dextran compared to no osmotic compression. Without dextran, the cross-bridge detachment rate slowed by ∼15% as sarcomere length increased, due to a slower MgADP release rate (11.2 ± 0.5 vs. 13.5 ± 0.7 s-1). In the presence of dextran, cross-bridge detachment was ∼20% slower at 2.5 vs. 2.0 μm sarcomere length due to a slower MgADP release rate (10.1 ± 0.6 vs. 12.9 ± 0.5 s-1). However, osmotic compression of fibers at either 2.5 or 2.0 μm sarcomere length produced only slight (and statistically insignificant) slowing in the rate of MgADP release. These data suggest that skeletal muscle exhibits sarcomere-length-dependent changes in cross-bridge kinetics and MgADP release that are separate from, or complementary to, changes in lattice spacing.
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13
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Wang Y, Burghardt TP. In vitro actin motility velocity varies linearly with the number of myosin impellers. Arch Biochem Biophys 2017; 618:1-8. [PMID: 28131772 DOI: 10.1016/j.abb.2017.01.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 01/23/2017] [Accepted: 01/24/2017] [Indexed: 11/26/2022]
Abstract
Cardiac myosin is the motor powering the heart. It moves actin with 3 step-size varieties generated by torque from the myosin heavy chain lever-arm rotation under the influence of myosin essential light chain whose N-terminal extension binds actin. Proposed mechanisms adapting myosin mechanochemical characteristics on the fly sometimes involve modulation of step-size selection probability via motor strain sensitivity. Strain following the power stroke, hypothetically imposed by the finite actin detachment rate 1/ton, is shown to have no effect on unloaded velocity when multiple myosins are simultaneously strongly actin bound in an in vitro motility assay. Actin filaments slide ∼2 native step-sizes while more than 1 myosin strongly binds actin probably ruling out an actin detachment limited model for imposing strain. It suggests that single myosin estimates for ton are too large, not applicable to the ensemble situation, or both. Parallel motility data quantitation involving instantaneous particle velocities (frame velocity) and actin filament track averaged velocities (track velocity) give an estimate of the random walk step-size, δ. Comparing δ for slow and fast motility components suggests the higher speed component has cardiac myosin upshifting to longer steps. Variable step-size characteristics imply cardiac myosin maintains a velocity dynamic range not involving strain.
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Affiliation(s)
- Y Wang
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, United States
| | - T P Burghardt
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, United States; Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, Rochester, MN 55905, United States.
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14
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Pulcastro HC, Awinda PO, Methawasin M, Granzier H, Dong W, Tanner BCW. Increased Titin Compliance Reduced Length-Dependent Contraction and Slowed Cross-Bridge Kinetics in Skinned Myocardial Strips from Rbm (20ΔRRM) Mice. Front Physiol 2016; 7:322. [PMID: 27524973 PMCID: PMC4966298 DOI: 10.3389/fphys.2016.00322] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 07/14/2016] [Indexed: 01/12/2023] Open
Abstract
Titin is a giant protein spanning from the Z-disk to the M-band of the cardiac sarcomere. In the I-band titin acts as a molecular spring, contributing to passive mechanical characteristics of the myocardium throughout a heartbeat. RNA Binding Motif Protein 20 (RBM20) is required for normal titin splicing, and its absence or altered function leads to greater expression of a very large, more compliant N2BA titin isoform in Rbm20 homozygous mice (Rbm20ΔRRM) compared to wild-type mice (WT) that almost exclusively express the stiffer N2B titin isoform. Prior studies using Rbm20ΔRRM animals have shown that increased titin compliance compromises muscle ultrastructure and attenuates the Frank-Starling relationship. Although previous computational simulations of muscle contraction suggested that increasing compliance of the sarcomere slows the rate of tension development and prolongs cross-bridge attachment, none of the reported effects of Rbm20ΔRRM on myocardial function have been attributed to changes in cross-bridge cycling kinetics. To test the relationship between increased sarcomere compliance and cross-bridge kinetics, we used stochastic length-perturbation analysis in Ca2+-activated, skinned papillary muscle strips from Rbm20ΔRRM and WT mice. We found increasing titin compliance depressed maximal tension, decreased Ca2+-sensitivity of the tension-pCa relationship, and slowed myosin detachment rate in myocardium from Rbm20ΔRRM vs. WT mice. As sarcomere length increased from 1.9 to 2.2 μm, length-dependent activation of contraction was eliminated in the Rbm20ΔRRM myocardium, even though myosin MgADP release rate decreased ~20% to prolong strong cross-bridge binding at longer sarcomere length. These data suggest that increasing N2BA expression may alter cardiac performance in a length-dependent manner, showing greater deficits in tension production and slower cross-bridge kinetics at longer sarcomere length. This study also supports the idea that passive mechanical characteristics of the myocardium influence ensemble cross-bridge behavior and maintenance of tension generation throughout the sarcomere.
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Affiliation(s)
- Hannah C Pulcastro
- Department of Integrative Physiology and Neuroscience, Washington State University Pullman, WA, USA
| | - Peter O Awinda
- Department of Integrative Physiology and Neuroscience, Washington State University Pullman, WA, USA
| | - Mei Methawasin
- Department of Cellular and Molecular Medicine, University of Arizona Tucson, AZ, USA
| | - Henk Granzier
- Department of Cellular and Molecular Medicine, University of Arizona Tucson, AZ, USA
| | - Wenji Dong
- Department of Integrative Physiology and Neuroscience, Washington State UniversityPullman, WA, USA; Voiland School of Chemical Engineering and Bioengineering, Washington State UniversityPullman, WA, USA
| | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University Pullman, WA, USA
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15
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Pulcastro HC, Awinda PO, Breithaupt JJ, Tanner BCW. Effects of myosin light chain phosphorylation on length-dependent myosin kinetics in skinned rat myocardium. Arch Biochem Biophys 2016; 601:56-68. [PMID: 26763941 DOI: 10.1016/j.abb.2015.12.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Revised: 12/14/2015] [Accepted: 12/29/2015] [Indexed: 11/19/2022]
Abstract
Myosin force production is Ca(2+)-regulated by thin-filament proteins and sarcomere length, which together determine the number of cross-bridge interactions throughout a heartbeat. Ventricular myosin regulatory light chain-2 (RLC) binds to the neck of myosin and modulates contraction via its phosphorylation state. Previous studies reported regional variations in RLC phosphorylation across the left ventricle wall, suggesting that RLC phosphorylation could alter myosin behavior throughout the heart. We found that RLC phosphorylation varied across the left ventricle wall and that RLC phosphorylation was greater in the right vs. left ventricle. We also assessed functional consequences of RLC phosphorylation on Ca(2+)-regulated contractility as sarcomere length varied in skinned rat papillary muscle strips. Increases in RLC phosphorylation and sarcomere length both led to increased Ca(2+)-sensitivity of the force-pCa relationship, and both slowed cross-bridge detachment rate. RLC-phosphorylation slowed cross-bridge rates of MgADP release (∼30%) and MgATP binding (∼50%) at 1.9 μm sarcomere length, whereas RLC phosphorylation only slowed cross-bridge MgATP binding rate (∼55%) at 2.2 μm sarcomere length. These findings suggest that RLC phosphorylation influences cross-bridge kinetics differently as sarcomere length varies and support the idea that RLC phosphorylation could vary throughout the heart to meet different contractile demands between the left and right ventricles.
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Affiliation(s)
- Hannah C Pulcastro
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164-7620, USA
| | - Peter O Awinda
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164-7620, USA
| | - Jason J Breithaupt
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164-7620, USA
| | - Bertrand C W Tanner
- Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA 99164-7620, USA.
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