Changes in cardiac muscle myosin light-chain phosphorylation associated with varying inotropic states |
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| Affiliation: | 1. Cardiology Section, Temple University, Philadelphia, Pennsylvania, USA;2. Department of Physiology, Temple University, Philadelphia, Pennsylvania, USA;1. Laboratory of Biochemistry, Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Tokushima, Japan;2. Institute of Pharmacognosy Attached to Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Tokushima, Japan;3. Department of Pharmaceutical Microbiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan;4. Institute for Advanced Biosciences, Keio University, Tsuruoka, Japan;5. Division of Enzyme Chemistry, Institute for Enzyme Research, Tokushima University, Tokushima, Japan;1. Department of Chemistry, University of Michigan, Ann Arbor, Michigan, USA;2. Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA;3. Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan, USA;1. Laboratory of Mucosal Barrier Pathobiology, Department of Pathology, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA;2. Department of Oncology, The First Affiliated Hospital of Soochow University, Jiangsu Key Laboratory of Neuropsychiatric Diseases and Cambridge-Suda (CAM-SU) Genomic Resource Center, Suzhou Medical School of Soochow University, Suzhou, China;3. Laboratory of Molecular Biology and Department of Biochemistry, Anhui Medical University, Hefei, Anhui, China;4. Gastroenterology Division, Department of Medicine, Beth-Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA |
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| Abstract: | Alterations in the phosphorylation of the 20,000-dalton cardiac muscle myosin light chain (LC2) have been associated with varying inotropic states of the myocardium exposed to catacholamines. It is not known if LC2 phosphorylation is altered when contractile function is enhanced or depressed as a result of varying the steady-state calcium activation in the isolated perfused myocardium. In this investigation the level of LC2 phosphorylation was measured in control (C) cardiac muscle, perfused with a medium containing 2.5 mm calcium; in mechanically depressed heart, perfused with 0.5 mm calcium (L-Ca); and in the myocardium with above normal contractile function, perfused with 4.5 mm calcium (H-Ca). The length-tension relationship was determined for all hearts perfused under control conditions and for those perfused with L-Ca and H-Ca. Subsequently, the myocardium was rapidly frozen, myosin LC2 isolated, and the phosphate content determined. Mechanical function of the myocardium was directly related to calcium activation (Peak tension C = 30.25 ± 3.27 mm Hg, L-Ca = 21.52 ± 3.92 mm Hg, H-Ca = 46.61 ± 11.79 mm Hg). The phosphorylation of LC2 varied inversely with the calcium concentration of the perfusing solution (slope = −0.134 (mole Pi/mole LC, mm Ca−1, intercept = 1.909; SEE 0.231; P < 0.05). The phosphate content of LC2 varied inversely with changes in peak tension (slope = −103 Δ% (mole Pi/mole LC)−1, intercept = 158, SEE = 0.156; P < 0.05).The precise mechanism through which light-chain phosphorylation is associated with the actin-myosin interaction remains to be elucidated. This study provides additional evidence of an association between contractile performance and myosin light-chain phosphorylation in cardiac muscle. It is apparent that the amount of free calcium present is important in this relationship. |
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