Artículos de revistas: "Myosin Myocardium"

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Buttrick, P., C. Perla, A. Malhotra, D. Geenen, M. Lahorra y J. Scheuer. "Effects of chronic dobutamine on cardiac mechanics and biochemistry after myocardial infarction in rats". American Journal of Physiology-Heart and Circulatory Physiology 260, n.º 2 (1 de febrero de 1991): H473—H479. http://dx.doi.org/10.1152/ajpheart.1991.260.2.h473.

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After myocardial infarction in rats, muscle performance in the remaining hypertrophied myocardium deteriorates and is associated with a decrease in myosin adenosinetriphosphatase (ATPase) activity and a shift to the V3 myosin heavy-chain isoform. We have previously shown in another model of hypertrophy, secondary to renovascular hypertension, that chronic intermittent adrenergic stimulation with dobutamine (Db) can prevent this biochemical adaptation. The present study was undertaken to assess the effects of chronic Db treatment on cardiac mass, function, metabolism, and myosin biochemistry in animals subjected to chronic myocardial infarction. Four groups of rats were studied: controls, animals treated with Db (2 mg/kg 2X daily for 4 wk), animals subjected to myocardial infarction and killed after 4 wk (MI), and MI animals concurrently treated with Db for 4 wk (MI-Db). The two MI groups were subdivided into those with and without congestive heart failure (CHF). Heart weight was increased by 13% with Db, unchanged in the infarct groups without CHF, and increased by 9 and 22% in the infarct groups with CHF. Db did not have any additional effect on heart weight in these later groups. Infarct weight was greatest in the animals with CHF, and viable myocardium was equivalent in all infarct groups suggesting that CHF was associated with a greater degree of hypertrophy. Ventricular performance, as assessed in an isovolumic heart apparatus, was markedly depressed in both infarct groups with CHF and was not affected by Db. Db increased myosin ATPase activity in control and infarcted animals both with and without congestive heart failure. Myosin oxygen consumption and lactate production were not adversely affected by Db.

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2

Larue, Catherine, Charles Calzolari, Jocelyne Léger, Jean Léger y Bernard Pau. "Immunoradiometric assay of myosin heavy chain fragments in plasma for investigation of myocardial infarction". Clinical Chemistry 37, n.º 1 (1 de enero de 1991): 78–82. http://dx.doi.org/10.1093/clinchem/37.1.78.

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Abstract Estimation of the extent and location of infarct is important for the prognosis and hence therapeutic strategy in patients with acute myocardial infarction (AMI). Because cardiac myosin is the major structural protein of the myocardium, and may thus reflect the extent of injured tissue, we established a new sensitive immunoradiometric assay, using a pair of monoclonal antibodies (Mabs) that specifically bind the myosin heavy chain fragments liberated from the myocyte into plasma after a heart attack. A first Mab is linked to a magnetic solid phase. A second Mab, radiolabeled with 125I, is used to detect myosin trapped on the solid phase by the first Mab during a 3-h incubation. This assay can detect 10 micro-units of myosin per liter and is highly reproducible.

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3

Locher, Matthew R., Maria V. Razumova, Julian E. Stelzer, Holly S. Norman y Richard L. Moss. "Effects of low-level α-myosin heavy chain expression on contractile kinetics in porcine myocardium". American Journal of Physiology-Heart and Circulatory Physiology 300, n.º 3 (marzo de 2011): H869—H878. http://dx.doi.org/10.1152/ajpheart.00452.2010.

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Myosin heavy chain (MHC) isoforms are principal determinants of work capacity in mammalian ventricular myocardium. The ventricles of large mammals including humans normally express ∼10% α-MHC on a predominantly β-MHC background, while in failing human ventricles α-MHC is virtually eliminated, suggesting that low-level α-MHC expression in normal myocardium can accelerate the kinetics of contraction and augment systolic function. To test this hypothesis in a model similar to human myocardium we determined composite rate constants of cross-bridge attachment ( fapp) and detachment ( gapp) in porcine myocardium expressing either 100% α-MHC or 100% β-MHC in order to predict the MHC isoform-specific effect on twitch kinetics. Right atrial (∼100% α-MHC) and left ventricular (∼100% β-MHC) tissue was used to measure myosin ATPase activity, isometric force, and the rate constant of force redevelopment ( ktr) in solutions of varying Ca2+ concentration. The rate of ATP utilization and ktr were approximately ninefold higher in atrial compared with ventricular myocardium, while tension cost was approximately eightfold greater in atrial myocardium. From these values, we calculated fapp to be ∼10-fold higher in α- compared with β-MHC, while gapp was 8-fold higher in α-MHC. Mathematical modeling of an isometric twitch using these rate constants predicts that the expression of 10% α-MHC increases the maximal rate of rise of force (dF/d tmax) by 92% compared with 0% α-MHC. These results suggest that low-level expression of α-MHC significantly accelerates myocardial twitch kinetics, thereby enhancing systolic function in large mammalian myocardium.

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Suematsu, Nobuhiro, Shinji Satoh, Shintaro Kinugawa, Hiroyuki Tsutsui, Shunji Hayashidani, Ryo Nakamura, Kensuke Egashira, Naoki Makino y Akira Takeshita. "α1-Adrenoceptor-Gq-RhoA signaling is upregulated to increase myofibrillar Ca2+ sensitivity in failing hearts". American Journal of Physiology-Heart and Circulatory Physiology 281, n.º 2 (1 de agosto de 2001): H637—H646. http://dx.doi.org/10.1152/ajpheart.2001.281.2.h637.

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α1-Adrenergic stimulation, coupled to Gq, has been shown to promote heart failure. However, the role of α1-adrenergic signaling in the regulation of myocardial contractility in failing myocardium is still poorly understood. To investigate this, we observed 1) the effect of phenylephrine on myofibrillar Ca2+ sensitivity in α-toxin-skinned cardiomyocytes, and 2) protein expression of Gq, RhoA, and myosin light chain phosphorylation using tachypacing-induced canine failing hearts. Phenylephrine significantly increased myofibrillar Ca2+ sensitivity in failing but not in normal cardiomyocytes. Whereas Y-27632 (Rho kinase inhibitor) blocked the phenylephrine-induced Ca2+ sensitization in the failing myocytes, calphostin C (protein kinase C inhibitor) had no effect on Ca2+ sensitization. The protein expression of Gαq and RhoA and the phosphorylation level of regulatory myosin light chain significantly increased in the failing myocardium. Our results suggest that α1-adrenoceptor-Gq signaling is upregulated in the failing myocardium to increase the myofibrillar Ca2+sensitivity mainly through the RhoA-Rho kinase pathway rather than through the protein kinase C pathway.

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5

Khalina, Yana, Sergey Udaltsov y Zoya A. Podlubnaya. "Ischemic myocardium: Behavior of myosin light chains". Journal of Molecular and Cellular Cardiology 34, n.º 6 (junio de 2002): A84. http://dx.doi.org/10.1016/s0022-2828(02)91028-x.

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6

Gregorich, Zachery R., Jitandrakumar R. Patel, Wenxuan Cai, Ziqing Lin, Rachel Heurer, Daniel P. Fitzsimons, Richard L. Moss y Ying Ge. "Deletion of Enigma Homologue from the Z-disc slows tension development kinetics in mouse myocardium". Journal of General Physiology 151, n.º 5 (14 de enero de 2019): 670–79. http://dx.doi.org/10.1085/jgp.201812214.

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Enigma Homologue (ENH) is a component of the Z-disc, a structure that anchors actin filaments in the contractile unit of muscle, the sarcomere. Cardiac-specific ablation of ENH protein expression causes contractile dysfunction that ultimately culminates in dilated cardiomyopathy. However, whether ENH is involved in the regulation of myocardial contractility is unknown. To determine if ENH is required for the mechanical activity of cardiac muscle, we analyze muscle mechanics of isolated trabeculae from the hearts of ENH+/+ and ENH−/− mice. We detected no differences in steady-state mechanical properties but show that when muscle fibers are allowed to relax and then are restretched, the rate at which tension redevelops is depressed in ENH−/− mouse myocardium relative to that in ENH+/+ myocardium. SDS-PAGE analysis demonstrated that the expression of β-myosin heavy chain is increased in ENH−/− mouse myocardium, which could partially, but not completely, account for the depression in tension redevelopment kinetics. Using top-down proteomics analysis, we found that the expression of other thin/thick filament regulatory proteins is unaltered, although the phosphorylation of a cardiac troponin T isoform, cardiac troponin I, and myosin regulatory light chain is decreased in ENH−/− mouse myocardium. Nevertheless, these alterations are very small and thus insufficient to explain slowed tension redevelopment kinetics in ENH−/− mouse myocardium. These data suggest that the ENH protein influences tension redevelopment kinetics in mouse myocardium, possibly by affecting cross-bridge cycling kinetics. Previous studies also indicate that ablation of specific Z-disc proteins in myocardium slows contraction kinetics, which could also be a contributing factor in this study.

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7

Toepfer, Christopher N., Markus B. Sikkel, Valentina Caorsi, Anupama Vydyanath, Iratxe Torre, O'Neal Copeland, Alexander R. Lyon et al. "A post-MI power struggle: adaptations in cardiac power occur at the sarcomere level alongside MyBP-C and RLC phosphorylation". American Journal of Physiology-Heart and Circulatory Physiology 311, n.º 2 (1 de agosto de 2016): H465—H475. http://dx.doi.org/10.1152/ajpheart.00899.2015.

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Myocardial remodeling in response to chronic myocardial infarction (CMI) progresses through two phases, hypertrophic “compensation” and congestive “decompensation.” Nothing is known about the ability of uninfarcted myocardium to produce force, velocity, and power during these clinical phases, even though adaptation in these regions likely drives progression of compensation. We hypothesized that enhanced cross-bridge-level contractility underlies mechanical compensation and is controlled in part by changes in the phosphorylation states of myosin regulatory proteins. We induced CMI in rats by left anterior descending coronary artery ligation. We then measured mechanical performance in permeabilized ventricular trabecula taken distant from the infarct zone and assayed myosin regulatory protein phosphorylation in each individual trabecula. During full activation, the compensated myocardium produced twice as much power and 31% greater isometric force compared with noninfarcted controls. Isometric force during submaximal activations was raised >2.4-fold, while power was 2-fold greater. Electron and confocal microscopy demonstrated that these mechanical changes were not a result of increased density of contractile protein and therefore not an effect of tissue hypertrophy. Hence, sarcomere-level contractile adaptations are key determinants of enhanced trabecular mechanics and of the overall cardiac compensatory response. Phosphorylation of myosin regulatory light chain (RLC) increased and remained elevated post-MI, while phosphorylation of myosin binding protein-C (MyBP-C) was initially depressed but then increased as the hearts became decompensated. These sensitivities to CMI are in accordance with phosphorylation-dependent regulatory roles for RLC and MyBP-C in crossbridge function and with compensatory adaptation in force and power that we observed in post-CMI trabeculae.

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8

Patel, Jitandrakumar R., Daniel P. Fitzsimons, Scott H. Buck, Mariappan Muthuchamy, David F. Wieczorek y Richard L. Moss. "PKA accelerates rate of force development in murine skinned myocardium expressing α- or β-tropomyosin". American Journal of Physiology-Heart and Circulatory Physiology 280, n.º 6 (1 de junio de 2001): H2732—H2739. http://dx.doi.org/10.1152/ajpheart.2001.280.6.h2732.

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In myocardium, protein kinase A (PKA) is known to phosphorylate troponin I (TnI) and myosin-binding protein-C (MyBP-C). Here, we used skinned myocardial preparations from nontransgenic (NTG) mouse hearts expressing 100% α-tropomyosin (α-Tm) to examine the effects of phosphorylated TnI and MyBP-C on Ca2+ sensitivity of force and the rate constant of force redevelopment ( k tr). Experiments were also done using transgenic (TG) myocardium expressing ∼60% β-Tm to test the idea that the α-Tm isoform is required to observe the mechanical effects of PKA phosphorylation. Compared with NTG myocardium, TG myocardium exhibited greater Ca2+sensitivity of force and developed submaximal forces at faster rates. Treatment with PKA reduced Ca2+ sensitivity of force in NTG and TG myocardium, had no effect on maximum k trin either NTG or TG myocardium, and increased the rates of submaximal force development in both kinds of myocardium. These results show that PKA-mediated phosphorylation of myofibrillar proteins significantly alters the static and dynamic mechanical properties of myocardium, and these effects occur regardless of the type of Tm expressed.

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9

Ma, Weikang, Marcus Henze, Robert L. Anderson, Henry Gong, Fiona L. Wong, Carlos L. del Rio y Thomas Irving. "The Super-Relaxed State and Length Dependent Activation in Porcine Myocardium". Circulation Research 129, n.º 6 (3 de septiembre de 2021): 617–30. http://dx.doi.org/10.1161/circresaha.120.318647.

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Rationale: Myofilament length-dependent activation (LDA) is the key underlying mechanism of cardiac heterometric autoregulation, commonly referred as the Frank-Starling Law of the heart. Although alterations in LDA are common in cardiomyopathic states, the precise structural and biochemical mechanisms underlying LDA remain unknown. Objective: Here, we examine the role of structural changes in the thick filament during diastole, in particular changes in the availability of myosin heads, in determining both calcium sensitivity and maximum contractile force during systole in permeabilized porcine cardiac fibers. Methods and Results: Permeabilized porcine fibers from ventricular myocardium were studied under relaxing conditions at short and long sarcomere length using muscle mechanics, biochemical measurements, and X-ray diffraction. Upon stretch, the porcine myocardium showed the increased calcium sensitivity and maximum calcium-activated force characteristic of LDA. Stretch increased diastolic ATP turnover, recruiting reserve myosin heads from the super-relaxed state at longer sarcomere length. Structurally, X-ray diffraction studies in the relaxed-muscle confirmed a departure from the helical ordering of the thick filament upon stretch which occurred concomitantly with a displacement of myosin heads towards actin, facilitating cross-bridge formation upon systolic activation. Mavacamten, a selective myosin-motor inhibitor known to weaken the transition to actin-bound power-generating states and to enrich the ordered super-relaxed state myosin population, reversed the structural effects of stretch on the thick filament, blunting the mechanical consequences of stretch; mavacamten did not, however, prevent other structural changes associated with LDA in the sarcomere, such as decreased lattice spacing or troponin-displacement. Conclusions: Our findings strongly indicate that in ventricular muscle, LDA and its systolic consequences are dependent on the population of myosin heads competent to form cross bridges and involves the recruitment of myosin heads from the reserve super-relaxed state pool during diastole.

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10

Bing, O. H., N. L. Hague, C. L. Perreault, C. H. Conrad, W. W. Brooks, S. Sen y J. P. Morgan. "Thyroid hormone effects on intracellular calcium and inotropic responses of rat ventricular myocardium". American Journal of Physiology-Heart and Circulatory Physiology 267, n.º 3 (1 de septiembre de 1994): H1112—H1121. http://dx.doi.org/10.1152/ajpheart.1994.267.3.h1112.

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To examine the mechanisms by which thyroid hormone modulates the inotropic state of rat myocardium, we studied the effects of thyroid state on isolated rat left ventricular papillary muscle function and intracellular calcium transients in the baseline state and in response to calcium and isoproterenol. Marked differences in contractile state of papillary muscles from hypothyroid and thyroid hormone-treated rats seen under baseline conditions (1.0 mM bath calcium, 30 degrees C, stimulation rate 12/min) do not appear to be due to differences in intracellular calcium concentration ([Ca2+]i) or to changes in myofilament calcium sensitivity but correlate with shifts in myosin isozyme distribution. In response to superimposed inotropic interventions (calcium, 0.625-5.0 mM, or isoproterenol, 10(-8)-10(-6) M), myocardial thyroid state modulates peak [Ca2+]i and inotropy, both of which are increased in thyroid hormone-treated relative to hypothyroid myocardium. The change in inotropy appears to be proportional to peak [Ca2+]i, whether mediated directly by calcium or as a result of beta-adrenergic stimulation. Thus, whereas baseline differences between hypothyroid and thyroid hormone-treated myocardium appear to be due to differences in myosin isozymes and presumed changes in adenosinetriphosphatase activity and cross-bridge cycling, superimposed inotropic responses appear to be mediated by changes in [Ca2+]i.

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11

Bobyk, V. I., D. V. Ryabenko, O. V. Sergienko, I. V. Trunina, O. M. Fedorkova, L. M. Morozova y L. L. Sidorik. "Experimental model of autoimmune myosin-induced myocardium injury". Biopolymers and Cell 23, n.º 2 (20 de marzo de 2007): 115–21. http://dx.doi.org/10.7124/bc.00075d.

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12

Chen, Peter P., Jitandrakumar R. Patel, Inna N. Rybakova, Jeffery W. Walker y Richard L. Moss. "Protein kinase A–induced myofilament desensitization to Ca2+ as a result of phosphorylation of cardiac myosin–binding protein C". Journal of General Physiology 136, n.º 6 (29 de noviembre de 2010): 615–27. http://dx.doi.org/10.1085/jgp.201010448.

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In skinned myocardium, cyclic AMP–dependent protein kinase A (PKA)-catalyzed phosphorylation of cardiac myosin–binding protein C (cMyBP-C) and cardiac troponin I (cTnI) is associated with a reduction in the Ca2+ responsiveness of myofilaments and an acceleration in the kinetics of cross-bridge cycling, although the respective contribution of these two proteins remains controversial. To further examine the relative roles that cTnI and cMyBP-C phosphorylation play in altering myocardial function, we determined the Ca2+ sensitivity of force (pCa50) and the activation dependence of the rate of force redevelopment (ktr) in control and PKA-treated mouse myocardium (isolated in the presence of 2,3-butanedione monoxime) expressing: (a) phosphorylatable cTnI and cMyBP-C (wild type [WT]), (b) phosphorylatable cTnI on a cMyBP-C–null background (cMyBP-C−/−), (c) nonphosphorylatable cTnI with serines23/24/43/45 and threonine144 mutated to alanines (cTnIAla5), and (d) nonphosphorylatable cTnI on a cMyBP-C–null background (cTnIAla5/cMyBP-C−/−). Here, PKA treatment decreased pCa50 in WT, cTnIAla5, and cMyBP-C−/− myocardium by 0.13, 0.08, and 0.09 pCa units, respectively, but had no effect in cTnIAla5/cMyBP-C−/− myocardium. In WT and cTnIAla5 myocardium, PKA treatment also increased ktr at submaximal levels of activation; however, PKA treatment did not have an effect on ktr in cMyBP-C−/− or cTnIAla5/cMyBP-C−/− myocardium. In addition, reconstitution of cTnIAla5/cMyBP-C−/− myocardium with recombinant cMyBP-C restored the effects of PKA treatment on pCa50 and ktr reported in cTnIAla5 myocardium. Collectively, these results indicate that the attenuation in myofilament force response to PKA occurs as a result of both cTnI and cMyBP-C phosphorylation, and that the reduction in pCa50 mediated by cMyBP-C phosphorylation most likely arises from an accelerated cross-bridge cycling kinetics partly as a result of an increased rate constant of cross-bridge detachment.

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13

Shimkunas, Rafael, Om Makwana, Kimberly Spaulding, Mona Bazargan, Michael Khazalpour, Kiyoaki Takaba, Mehrdad Soleimani et al. "Myofilament dysfunction contributes to impaired myocardial contraction in the infarct border zone". American Journal of Physiology-Heart and Circulatory Physiology 307, n.º 8 (15 de octubre de 2014): H1150—H1158. http://dx.doi.org/10.1152/ajpheart.00463.2014.

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After myocardial infarction, a poorly contracting nonischemic border zone forms adjacent to the infarct. The cause of border zone dysfunction is unclear. The goal of this study was to determine the myofilament mechanisms involved in postinfarction border zone dysfunction. Two weeks after anteroapical infarction of sheep hearts, we studied in vitro isometric and isotonic contractions of demembranated myocardium from the infarct border zone and a zone remote from the infarct. Maximal force development (Fmax) of the border zone myocardium was reduced by 31 ± 2% versus the remote zone myocardium ( n = 6/group, P < 0.0001). Decreased border zone Fmax was not due to a reduced content of contractile material, as assessed histologically, and from myosin content. Furthermore, decreased border zone Fmax did not involve altered cross-bridge kinetics, as assessed by muscle shortening velocity and force development kinetics. Decreased border zone Fmax was associated with decreased cross-bridge formation, as assessed from muscle stiffness in the absence of ATP where cross-bridge formation should be maximized (rigor stiffness was reduced 34 ± 6%, n = 5, P = 0.011 vs. the remote zone). Furthermore, the border zone myocardium had significantly reduced phosphorylation of myosin essential light chain (ELC; 41 ± 10%, n = 4, P < 0.05). However, for animals treated with doxycycline, an inhibitor of matrix metalloproteinases, rigor stiffness and ELC phosphorylation were not reduced in the border zone myocardium, suggesting that doxycycline had a protective effect. In conclusion, myofilament dysfunction contributes to postinfarction border zone dysfunction, myofilament dysfunction involves impaired cross-bridge formation and decreased ELC phosphorylation, and matrix metalloproteinase inhibition may be beneficial for limiting postinfarct border zone dysfunction.

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Klibanov, Alexander L., Ban An Khaw, Naseem Nossiff, Sean M. O'Donnell, Leaf Huang, Mikhail A. Slinkin y Vladimir P. Torchilin. "Targeting of macromolecular carriers and liposomes by antibodies to myosin heavy chain". American Journal of Physiology-Lung Cellular and Molecular Physiology 261, n.º 4 (1 de octubre de 1991): L60—L65. http://dx.doi.org/10.1152/ajplung.1991.261.4.l60.

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Macromolecular carriers and liposomes were covalently coupled to monoclonal antibodies against cardiac myosin heavy chain. Deferoxamine-modified polymers bound tightly with 67Ga and68 Ga radioisotopes. Ternary deferoxamine-polylysine antibody conjugates specifically targeted the radioisotopes to a myosin-coated microplate. Scatchard analysis revealed a high affinity of the conjugate for the target with a Kas of ≈108 M-1. Liposomes that contained immobilized antimyosin antibodies were targeted specifically to the myosin-coated plate. Additional coating of these liposomes with polyethylene glycol reduced specific binding to the target in vitro. However, because of the presence of polyethylene glycol on the surface of liposomes, these liposomes had a long half-life and slowly cleared from the bloodstream after intravenous injection. These immunoliposomes showed up to 16- to 18-fold specific localization to the necrotic areas of the myocardium in rabbits with experimental infarction. antimyosin; chelating polymer; liposome; monoclonal antibody; myocardial infarction; radioimmunoimaging

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Klibanov, Alexander L., Ban An Khaw, Naseem Nossiff, Sean M. O'Donnell, Leaf Huang, Mikhail A. Slinkin y Vladimir P. Torchilin. "Targeting of macromolecular carriers and liposomes by antibodies to myosin heavy chain". American Journal of Physiology-Heart and Circulatory Physiology 261, n.º 4 (1 de octubre de 1991): 60–65. http://dx.doi.org/10.1152/ajpheart.1991.261.4.60.

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Macromolecular carriers and liposomes were covalently coupled to monoclonal antibodies against cardiac myosin heavy chain. Deferoxamine-modified polymers bound tightly with 67Ga and 68Ga radioisotopes. Ternary deferoxamine-polylysine antibody conjugates specifically targeted the radioisotopes to a myosin-coated microplate. Scatchard analysis revealed a high affinity of the conjugate for the target with a Kas of ≈108 M-1. Liposomes that contained immobilized antimyosin antibodies were targeted specifically to the myosin-coated plate. Additional coating of these liposomes with polyethylene glycol reduced specific binding to the target in vitro. However, because of the presence of polyethylene glycol on the surface of liposomes, these liposomes had a long half-life and slowly cleared from the bloodstream after intravenous injection. These immunoliposomes showed up to 16- to 18-fold specific localization to the necrotic areas of the myocardium in rabbits with experimental infarction. antimyosin; chelating polymer; liposome; monoclonal antibody; myocardial infarction; radioimmunoimaging

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SCHIAFFINO, S., L. GORZA, S. SARTORE y L. SAGGIN. "Cardiac myosins: Distribution of myosin heavy chain isoforms in ordinary myocardium and conduction tissue". Journal of Molecular and Cellular Cardiology 17 (1985): 33. http://dx.doi.org/10.1016/s0022-2828(85)80243-1.

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17

Nishikawa, T., S. Ishiyama, K. Takeda, T. Kasajima, S. Abe, T. Shimojo, H. Ito y M. Hiroe. "Programmed Cell Death (Apoptosis) in the Myocardium with Acute Myocarditis." Microscopy and Microanalysis 3, S2 (agosto de 1997): 63–64. http://dx.doi.org/10.1017/s1431927600007200.

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Acute myocarditis is a potentially lethal disease. However, the precise mechanism of myocardial damage in myocarditis is still unknown, although its pathogenesis seems to be involved in the result of natural killer cells, cytotoxic T cells and autoantibodies. Recently, it has been reported that programmed death of cardiac myocytes can be induced by several pathological conditions including infarction and end-stage cardiac failure. However, little is known about the myocardial cell death in myocarditis. In this study, we investigated whether myocardial cell death via apoptosis occurs in the heart tissue with myocarditis.Since it has been reported that the pathogenesis of the tissue damage in viral myocarditis resembles that in experimental autoimmune myocarditis induced by myosin, we used an experimental model for autoimmune myocarditis induced in Lewis rat with the use of myosin as the antigen. Rats were sacrificed on days 14, 17 and 21 after myosin injection. The tissue specimens were taken from ventricle of the heart.

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18

Hornby, L., N. Hamilton, D. Marshall, T. A. Salerno, M. H. Laughlin y C. D. Ianuzzo. "Role of cardiac work in regulating myocardial biochemical characteristics". American Journal of Physiology-Heart and Circulatory Physiology 258, n.º 5 (1 de mayo de 1990): H1482—H1490. http://dx.doi.org/10.1152/ajpheart.1990.258.5.h1482.

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The purpose of this study was to determine the extent to which functional demand regulates the biochemical character and enzyme capacities of the rat myocardium. Hearts from donor rats were heterotopically transplanted onto the abdominal aorta and inferior vena cava of isogenic recipients. The procedure results in a perfused but nonpumping heart that has a reduced heart rate (HR) and performs essentially no stroke work (SW). After 30 days, metabolic enzyme activities (phosphorylase, 6-phosphofructokinase, citrate synthase, and 3-hydroxyacyl-CoA dehydrogenase) were significantly lower (40-60%) in the nonworking heart. Specific sarcoplasmic reticulum Ca2(+)-adenosinetriphosphatase (ATPase) activity was unchanged, but activity per gram of heart was 41% lower. Myosin isozymes were 58% V1, 21% V2, and 21% V3 in the nonworking heart compared with 100% V1 in the working heart. Myosin and myofibrillar ATPase activities each decreased by 28%. These findings suggest that both HR and SW play major and specific roles in regulating myocardial biochemical capacities and determining the myosin phenotype.

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Rao, Vijay S., Laura R. La Bonte, Yaqin Xu, Zequan Yang, Brent A. French y William H. Guilford. "Alterations to myofibrillar protein function in nonischemic regions of the heart early after myocardial infarction". American Journal of Physiology-Heart and Circulatory Physiology 293, n.º 1 (julio de 2007): H654—H659. http://dx.doi.org/10.1152/ajpheart.01314.2006.

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Remote-zone left ventricular dysfunction (LVD) contributes to global reductions in contractile function after localized myocardial infarction (MI). However, the molecular mechanisms underlying this form of LVD are not clear. This study tested the hypothesis that myofibrillar protein function is directly affected in remote-zone LVD early after MI. Cardiac myosin and native thin filaments were purified from mouse myocardium taken from both the nonnecrotic zone adjacent to and the nonischemic zone remote from an infarct induced by 1 h of coronary occlusion followed by 24 h of reperfusion. Thin filament velocities were measured using the in vitro motility assay. Results showed that overall function was significantly reduced in samples from both the adjacent (43 ± 12% of control, n = 7) and remote (53 ± 8% of control, n = 13) zones when compared with control proteins ( P < 0.05). Myosin from the remote zone propelled control thin filaments at reduced velocities similar to those measured above. In contrast, the Ca2+ sensitivity of remote-zone thin filaments over control myosin was unchanged from control thin filaments (half-maximal at pCa 6.32 ± 0.08 and 6.27 ± 0.06, respectively) but showed a 20% increase in velocity at saturating Ca2+ that parallels an increase in tropomyosin phosphorylation. Myosin dysfunction may be related to oxidation of cysteines in the myosin heavy chains or carbonylation of myosin binding protein-C. We hypothesize that phosphorylation of tropomyosin may serve a compensatory role, augmenting contraction during periods of oxidative stress when myosin function is compromised.

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SILVER, P., L. BUJA y J. STULL. "Frequency-dependent myosin light chain phosphorylation in isolated myocardium". Journal of Molecular and Cellular Cardiology 18, n.º 1 (enero de 1986): 31–37. http://dx.doi.org/10.1016/s0022-2828(86)80980-4.

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Tanner, Bertrand C. W., Michael J. Previs, Yuan Wang, Jeffrey Robbins y Bradley M. Palmer. "Cardiac myosin binding protein-C phosphorylation accelerates β-cardiac myosin detachment rate in mouse myocardium". American Journal of Physiology-Heart and Circulatory Physiology 320, n.º 5 (1 de mayo de 2021): H1822—H1835. http://dx.doi.org/10.1152/ajpheart.00673.2020.

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Length perturbation analysis was used to demonstrate that β-cardiac myosin characteristic rates of detachment and recruitment in the intact myofilament lattice are accelerated by Pi, phosphorylation of cMyBP-C, and the absence of cMyBP-C. The results suggest that cMyBP-C normally slows myosin detachment, including Pi-dependent detachment, and that this inhibition is released with phosphorylation or absence of cMyBP-C.

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Stelzer, Julian E., Jitandrakumar R. Patel y Richard L. Moss. "Acceleration of Stretch Activation in Murine Myocardium due to Phosphorylation of Myosin Regulatory Light Chain". Journal of General Physiology 128, n.º 3 (14 de agosto de 2006): 261–72. http://dx.doi.org/10.1085/jgp.200609547.

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The regulatory light chains (RLCs) of vertebrate muscle myosins bind to the neck region of the heavy chain domain and are thought to play important structural roles in force transmission between the cross-bridge head and thick filament backbone. In vertebrate striated muscles, the RLCs are reversibly phosphorylated by a specific myosin light chain kinase (MLCK), and while phosphorylation has been shown to accelerate the kinetics of force development in skeletal muscle, the effects of RLC phosphorylation in cardiac muscle are not well understood. Here, we assessed the effects of RLC phosphorylation on force, and the kinetics of force development in myocardium was isolated in the presence of 2,3-butanedione monoxime (BDM) to dephosphorylate RLC, subsequently skinned, and then treated with MLCK to phosphorylate RLC. Since RLC phosphorylation may be an important determinant of stretch activation in myocardium, we recorded the force responses of skinned myocardium to sudden stretches of 1% of muscle length both before and after treatment with MLCK. MLCK increased RLC phosphorylation, increased the Ca2+ sensitivity of isometric force, reduced the steepness of the force–pCa relationship, and increased both Ca2+-activated and Ca2+-independent force. Sudden stretch of myocardium during an otherwise isometric contraction resulted in a concomitant increase in force that quickly decayed to a minimum and was followed by a delayed redevelopment of force, i.e., stretch activation, to levels greater than pre-stretch force. MLCK had profound effects on the stretch activation responses during maximal and submaximal activations: the amplitude and rate of force decay after stretch were significantly reduced, and the rate of delayed force recovery was accelerated and its amplitude reduced. These data show that RLC phosphorylation increases force and the rate of cross-bridge recruitment in murine myocardium, which would increase power generation in vivo and thereby enhance systolic function.

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Pulcastro, Hannah C., Peter O. Awinda, Jason J. Breithaupt y Bertrand C. W. Tanner. "Effects of myosin light chain phosphorylation on length-dependent myosin kinetics in skinned rat myocardium". Archives of Biochemistry and Biophysics 601 (julio de 2016): 56–68. http://dx.doi.org/10.1016/j.abb.2015.12.014.

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24

Sarin, Vandana, Mariappan Muthuchamy y Cristine L. Heaps. "Ca2+ sensitization of cardiac myofilament proteins contributes to exercise training-enhanced myocardial function in a porcine model of chronic occlusion". American Journal of Physiology-Heart and Circulatory Physiology 301, n.º 4 (octubre de 2011): H1579—H1587. http://dx.doi.org/10.1152/ajpheart.00294.2011.

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Exercise training has been shown to improve cardiac dysfunction in both patients and animal models of coronary artery disease; however, the underlying cellular and molecular mechanisms have not been completely understood. We hypothesized that exercise training would improve force generation in the myocardium distal to chronic coronary artery occlusion via altered intracellular Ca2+ concentration ([Ca2+]i) cycling and/or Ca2+ sensitization of myofilaments. Ameroid occluders were surgically placed around the proximal left circumflex coronary artery of adult female Yucatan pigs. Twenty-two weeks postoperatively, the myocardium was isolated from nonoccluded (left anterior descending artery dependent) and collateral-dependent (formerly left circumflex coronary artery dependent) regions of sedentary (pen confined) and exercise-trained (treadmill run, 5 days/wk for 14 wk) pigs. Force measurements in myocardial strips showed that the percent change in force at stimulation frequencies of 3 and 4 Hz relative to 1 Hz was significantly higher in exercise-trained pigs compared with sedentary pigs. β-Adrenergic stimulation with dobutamine significantly improved force kinetics in myocardial strips of sedentary but not exercise-trained pigs at 1 Hz. Additionally, time to peak and half-decay of intracellular Ca2+ (340-to-380-nm fluoresence ratio) responses at 1 Hz were significantly decreased in the collateral-dependent region of exercise-trained pigs with no difference in peak [Ca2+]i between groups. Furthermore, the skinned myocardium from exercise-trained pigs showed an increase in Ca2+ sensitivity compared with sedentary pigs. Immunoblot analysis revealed that the relative levels of cardiac troponin T and β1-adrenergic receptors were decreased in hearts from exercise-trained pigs independent of occlusion. Also, the ratio of phosphorylated to total myosin light chain-2, basal phosphorylation levels of cardiac troponin I (Ser23 and Ser24), and cardiac myosin binding protein-C (Ser282) were unaltered by occlusion or exercise training. Thus, our data demonstrate that exercise training-enhanced force generation in the nonoccluded and collateral-dependent myocardium was associated with improved Ca2+ transients, increased Ca2+ sensitization of myofilament proteins, and decreased expression levels of β1-adrenergic receptors and cardiac troponin T.

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25

Wehman, Brody, Sudhish Sharma, Nicholas Pietris, Rachana Mishra, Osama T. Siddiqui, Grace Bigham, Tieluo Li et al. "Mesenchymal stem cells preserve neonatal right ventricular function in a porcine model of pressure overload". American Journal of Physiology-Heart and Circulatory Physiology 310, n.º 11 (1 de junio de 2016): H1816—H1826. http://dx.doi.org/10.1152/ajpheart.00955.2015.

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Limited therapies exist for patients with congenital heart disease (CHD) who develop right ventricular (RV) dysfunction. Bone marrow-derived mesenchymal stem cells (MSCs) have not been evaluated in a preclinical model of pressure overload, which simulates the pathophysiology relevant to many forms of CHD. A neonatal swine model of RV pressure overload was utilized to test the hypothesis that MSCs preserve RV function and attenuate ventricular remodeling. Immunosuppressed Yorkshire swine underwent pulmonary artery banding to induce RV dysfunction. After 30 min, human MSCs (1 million cells, n = 5) or placebo ( n = 5) were injected intramyocardially into the RV free wall. Serial transthoracic echocardiography monitored RV functional indices including 2D myocardial strain analysis. Four weeks postinjection, the MSC-treated myocardium had a smaller increase in RV end-diastolic area, end-systolic area, and tricuspid vena contracta width ( P < 0.01), increased RV fractional area of change, and improved myocardial strain mechanics relative to placebo ( P < 0.01). The MSC-treated myocardium demonstrated enhanced neovessel formation ( P < 0.0001), superior recruitment of endogenous c-kit+ cardiac stem cells to the RV ( P < 0.0001) and increased proliferation of cardiomyocytes ( P = 0.0009) and endothelial cells ( P < 0.0001). Hypertrophic changes in the RV were more pronounced in the placebo group, as evidenced by greater wall thickness by echocardiography ( P = 0.008), increased cardiomyocyte cross-sectional area ( P = 0.001), and increased expression of hypertrophy-related genes, including brain natriuretic peptide, β-myosin heavy chain and myosin light chain. Additionally, MSC-treated myocardium demonstrated increased expression of the antihypertrophy secreted factor, growth differentiation factor 15 (GDF15), and its downstream effector, SMAD 2/3, in cultured neonatal rat cardiomyocytes and in the porcine RV myocardium. This is the first report of the use of MSCs as a therapeutic strategy to preserve RV function and attenuate remodeling in the setting of pressure overload. Mechanistically, transplanted MSCs possibly stimulated GDF15 and its downstream SMAD proteins to antagonize the hypertrophy response of pressure overload. These encouraging results have implications in congenital cardiac pressure overload lesions.

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26

Li, King-Lun, Mei Methawasin, Bertrand C. W. Tanner, Henk L. Granzier, R. John Solaro y Wen-Ji Dong. "Sarcomere length–dependent effects on Ca2+-troponin regulation in myocardium expressing compliant titin". Journal of General Physiology 151, n.º 1 (6 de diciembre de 2018): 30–41. http://dx.doi.org/10.1085/jgp.201812218.

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Cardiac performance is tightly regulated at the cardiomyocyte level by sarcomere length, such that increases in sarcomere length lead to sharply enhanced force generation at the same Ca2+ concentration. Length-dependent activation of myofilaments involves dynamic and complex interactions between a multitude of thick- and thin-filament components. Among these components, troponin, myosin, and the giant protein titin are likely to be key players, but the mechanism by which these proteins are functionally linked has been elusive. Here, we investigate this link in the mouse myocardium using in situ FRET techniques. Our objective was to monitor how length-dependent Ca2+-induced conformational changes in the N domain of cardiac troponin C (cTnC) are modulated by myosin–actin cross-bridge (XB) interactions and increased titin compliance. We reconstitute FRET donor- and acceptor-modified cTnC(13C/51C)AEDANS-DDPM into chemically skinned myocardial fibers from wild-type and RBM20-deletion mice. The Ca2+-induced conformational changes in cTnC are quantified and characterized using time-resolved FRET measurements as XB state and sarcomere length are varied. The RBM20-deficient mouse expresses a more compliant N2BA titin isoform, leading to reduced passive tension in the myocardium. This provides a molecular tool to investigate how altered titin-based passive tension affects Ca2+-troponin regulation in response to mechanical stretch. In wild-type myocardium, we observe a direct association of sarcomere length–dependent enhancement of troponin regulation with both Ca2+ activation and strongly bound XB states. In comparison, measurements from titin RBM20-deficient animals show blunted sarcomere length–dependent effects. These results suggest that titin-based passive tension contributes to sarcomere length–dependent Ca2+-troponin regulation. We also conclude that strong XB binding plays an important role in linking the modulatory effect of titin compliance to Ca2+-troponin regulation of the myocardium.

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27

Liu, Haidun, Mary Henein, Maria Anillo y John F. Dawson. "Cardiac actin changes in the actomyosin interface have different effects on myosin duty ratio". Biochemistry and Cell Biology 96, n.º 1 (febrero de 2018): 26–31. http://dx.doi.org/10.1139/bcb-2017-0136.

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Hypertrophic cardiomyopathy (HCM) is an inherited cardiovascular disease (CD) that commonly causes an increased size of cardiomyocytes in the left ventricle. The proteins myosin and actin interact in the myocardium to produce contraction through the actomyosin ATPase cycle. The duty ratio (r) of myosin is the proportion of the actomyosin ATPase cycle that myosin is bound to actin and does work. A common hypothesis is that HCM mutations increase contraction in cardiac sarcomeres; however, the available data are not clear on this connection. Based on previous work with human α-cardiac actin (ACTC), we hypothesize that HCM-linked ACTC variants with alterations near the myosin binding site have an increased r, producing more force. Myosin duty ratios using human ACTC variant proteins were calculated with myosin ATPase activity and in-vitro motility data. We found no consistent changes in the duty ratio of the ACTC variants, suggesting that other factors are involved in the development of HCM when ACTC variants are present.

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28

Laughlin, M. H., C. C. Hale, L. Novela, D. Gute, N. Hamilton y C. D. Ianuzzo. "Biochemical characterization of exercise-trained porcine myocardium". Journal of Applied Physiology 71, n.º 1 (1 de julio de 1991): 229–35. http://dx.doi.org/10.1152/jappl.1991.71.1.229.

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The purpose of this study was to determine whether cardiac biochemical adaptations are induced by chronic exercise training (ET) of miniature swine. Female Yucatan miniature swine were trained on a treadmill or were cage confined (C) for 16–22 wk. After training, the ET pigs had increased exercise tolerance, lower heart rates during exercise at submaximal intensities, moderate cardiac hypertrophy, increased coronary blood flow capacity, and increased oxidative capacity of skeletal muscle. Myosin from both the C and ET hearts was 100% of the V3 isozyme, and there were no differences between the myosin adenosine triphosphatase (ATPase) or myofibrillar ATPase activities of C and ET hearts. Also, the sarcoplasmic reticulum Ca(2+)-ATPase activity and Na(+)-Ca2+ exchange activity of sarcolemmal vesicles were the same in cardiac muscle of C and ET hearts. Finally, the glycolytic and oxidative capacity of ET cardiac muscle was not different from control, since phosphofructokinase, citrate synthase, and 3-hydroxyacyl-CoA dehydrogenase activities were the same in cardiac tissue from ET and C pigs. We conclude that endurance exercise training does not provide sufficient stress on the heart of a large mammal to induce changes in any of the three major cardiac biochemical systems of the porcine myocardium: the contractile system, the Ca2+ regulatory systems, or the metabolic system.

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29

Parker, Thomas G. y James N. Tsoporis. "Induction of S100β in Myocardium: An Intrinsic Inhibitor of Cardiac Hypertrophy". Canadian Journal of Applied Physiology 23, n.º 4 (1 de agosto de 1998): 377–89. http://dx.doi.org/10.1139/h98-022.

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Cardiac hypertrophy induced by pressure overload and following myocardial infarction entails regulation of myocardial gene expression, recapitulating an embryonic phenotype, including activation of fetal β-myosin heavy chain and skeletal α-actin. Progressive hypertrophy and alterations in gene expression may contribute to myocardial failure. Although signaling pathways that contribute to hypertrophy development have been identified, intrinsic cardiac regulators that limit hypertrophic response have not been determined. The β subunit of S100 protein is induced in the myocardium of human subjects and an experimental rat model following myocardial infarction. Forced S100β expression in neonatal rat cardiac myocyte cultures and high level expression of S100β in transgenic mice hearts inhibit cardiac hypertrophy and the associated phenotype by modulating protein kinase C-dependent pathways. S100β expression is probably a component of the myocyte response to trophic stimulation that serves as a negative feedback mechanism to limit cellular growth and the associated alterations in gene expression. Key words: gene expression, cardiac myocytes, growth factors, heart failure, calcium-binding proteins

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30

Ait-Mou, Younss, Karen Hsu, Gerrie P. Farman, Mohit Kumar, Marion L. Greaser, Thomas C. Irving y Pieter P. de Tombe. "Titin strain contributes to the Frank–Starling law of the heart by structural rearrangements of both thin- and thick-filament proteins". Proceedings of the National Academy of Sciences 113, n.º 8 (8 de febrero de 2016): 2306–11. http://dx.doi.org/10.1073/pnas.1516732113.

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The Frank–Starling mechanism of the heart is due, in part, to modulation of myofilament Ca2+ sensitivity by sarcomere length (SL) [length-dependent activation (LDA)]. The molecular mechanism(s) that underlie LDA are unknown. Recent evidence has implicated the giant protein titin in this cellular process, possibly by positioning the myosin head closer to actin. To clarify the role of titin strain in LDA, we isolated myocardium from either WT or homozygous mutant (HM) rats that express a giant splice isoform of titin, and subjected the muscles to stretch from 2.0 to 2.4 μm of SL. Upon stretch, HM compared with WT muscles displayed reduced passive force, twitch force, and myofilament LDA. Time-resolved small-angle X-ray diffraction measurements of WT twitching muscles during diastole revealed stretch-induced increases in the intensity of myosin (M2 and M6) and troponin (Tn3) reflections, as well as a reduction in cross-bridge radial spacing. Independent fluorescent probe analyses in relaxed permeabilized myocytes corroborated these findings. X-ray electron density reconstruction revealed increased mass/ordering in both thick and thin filaments. The SL-dependent changes in structure observed in WT myocardium were absent in HM myocardium. Overall, our results reveal a correlation between titin strain and the Frank–Starling mechanism. The molecular basis underlying this phenomenon appears not to involve interfilament spacing or movement of myosin toward actin but, rather, sarcomere stretch-induced simultaneous structural rearrangements within both thin and thick filaments that correlate with titin strain and myofilament LDA.

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31

Bottinelli, R., M. Canepari, V. Cappelli y C. Reggiani. "Maximum speed of shortening and ATPase activity in atrial and ventricular myocardia of hyperthyroid rats". American Journal of Physiology-Cell Physiology 269, n.º 3 (1 de septiembre de 1995): C785—C790. http://dx.doi.org/10.1152/ajpcell.1995.269.3.c785.

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The kinetic properties of the myofibrillar system of atrial and ventricular myocardia of hyperthyroid rats were analyzed by determining ATPase activity and maximum shortening velocity. Hyperthyroidism was induced by daily subcutaneous injections of triiodothyronine (0.2 mg/kg body wt) for 2 wk. The treatment induced a marked atrial and ventricular hypertrophy and, in ventricular myocardium, an isomyosin shift toward a homogeneous V1 composition. Skinned trabeculae and purified myofibrils were prepared from atrial and ventricular myocardia. Enzymatic assays on the myofibrils showed that both Ca-stimulated ATPase activity and Ca-Mg-dependent ATPase activity had equal values in atrial and ventricular myocardia. In skinned trabeculae during maximal Ca activations, force-velocity curves were determined by load-clamp maneuvers, and unloaded shortening velocity (Vo) was obtained with the slack-test method. Both maximum shortening velocities extrapolated from the force-velocity curves (Vmax) and Vo were significantly higher (+68 and +52%, respectively) in atrial than in ventricular preparations. Developed tension was significantly greater in ventricular preparations. Maximum power output was not significantly different. Previous findings (V. Cappelli, R. Bottinelli, C. Poggesi, R. Moggio, and C. Reggiani. Circ. Res. 65: 446-457, 1989) had led to the conclusion that variations in ATPase activity and shortening velocity of ventricular myocardium can be accounted for by changes in isomyosin composition. In this light, the present results suggest that 1) ATPase activity is equal in atrial and ventricular myocardia as the two tissues contain the same myosin heavy chain isoform, 2) the difference in maximum speed of shortening between atrium and ventricle might be due to the presence of tissue-specific isoforms of myosin light chains.

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32

Wang, Guan-Ying, Diana T. McCloskey, Sally Turcato, Philip M. Swigart, Paul C. Simpson y Anthony J. Baker. "Contrasting inotropic responses to α1-adrenergic receptor stimulation in left versus right ventricular myocardium". American Journal of Physiology-Heart and Circulatory Physiology 291, n.º 4 (octubre de 2006): H2013—H2017. http://dx.doi.org/10.1152/ajpheart.00167.2006.

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The left ventricle (LV) and right ventricle (RV) have differing hemodynamics and embryological origins, but it is unclear whether they are regulated differently. In particular, no previous studies have directly compared the LV versus RV myocardial inotropic responses to α1-adrenergic receptor (α1-AR) stimulation. We compared α1-AR inotropy of cardiac trabeculae from the LV versus RV of adult mouse hearts. As previously reported, for mouse RV trabeculae, α1-AR stimulation with phenylephrine (PE) caused a triphasic contractile response with overall negative inotropy. In marked contrast, LV trabeculae had an overall positive inotropic response to PE. Stimulation of a single subtype (α1A-AR) with A-61603 also mediated contrasting LV/RV inotropy, suggesting differential activation of multiple α1-AR-subtypes was not involved. Contrasting LV/RV α1-AR inotropy was not abolished by inhibiting protein kinase C, suggesting differential activation of PKC isoforms was not involved. However, contrasting LV/RV α1-AR inotropic responses did involve different effects on myofilament Ca2+ sensitivity: submaximal force of skinned trabeculae was increased by PE pretreatment for LV but was decreased by PE for RV. For LV myocardium, α1-AR-induced net positive inotropy was abolished by the myosin light chain kinase inhibitor ML-9. This study suggests that LV and RV myocardium have fundamentally different inotropic responses to α1-AR stimulation, involving different effects on myofilament function and myosin light chain phosphorylation.

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33

Mozaffari, Mahmood S., Glenn L. Wilson y Stephen W. Schaffer. "Effect of chronic sulfonylurea treatment on the myocardium of insulin-dependent diabetic rats". Canadian Journal of Physiology and Pharmacology 66, n.º 12 (1 de diciembre de 1988): 1481–86. http://dx.doi.org/10.1139/y88-242.

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Adult rats treated with high doses of streptozocin became progressively more hyperglycemic during the first month of the diabetic condition. Treatment of these rats with the sulfonylurea glyburide halted, and in some cases, reversed this process in a high percentage of the diabetics. Associated with the glyburide-mediated improvement in fasting blood glucose levels was an increase in myocardial glucose utilization and lactate production. The stimulation of myocardial glucose utilization by insulin was greater in glyburide-treated hearts, indicating that the hyperglycemic agent increased insulin responsiveness. The sulfonylurea also partially restored insulin sensitivity to the normal range. In agreement with previous studies, myocardial mechanical function was significantly impaired in the diabetic heart. When treated with glyburide, the severity of the mechanical defect was significantly less. The sulfonylurea also promoted an increase in myosin ATPase activity and a shift in the myosin isozyme pattern in favour of the most active V1 form. These results imply that glyburide therapy can provide benefit to the diabetic heart by improving energy metabolism and promoting a shift in myosin towards the most active form.

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Stepanova, O. V., A. V. Chadin, A. A. Raevskaya, D. A. Blejyants, R. M. Muratov y V. P. Shirinsky. "Myosin-activating protein kinases in human myocardium: Localization and content". Biophysics 53, n.º 5 (octubre de 2008): 366–70. http://dx.doi.org/10.1134/s0006350908050084.

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35

Syrový, I. "Expression of myosin in atrial areas of the bovine myocardium". Comparative Biochemistry and Physiology Part A: Physiology 92, n.º 3 (enero de 1989): 441–43. http://dx.doi.org/10.1016/0300-9629(89)90589-6.

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LYN, DEBORAH, XIAOWEI LIU, NICOLE A. BENNETT y NERIMIAH L. EMMETT. "Gene expression profile in mouse myocardium after ischemia". Physiological Genomics 2, n.º 3 (27 de abril de 2000): 93–100. http://dx.doi.org/10.1152/physiolgenomics.2000.2.3.93.

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Lyn, Deborah, Xiaowei Liu, Nicole A. Bennett, and Nerimiah L. Emmett. Gene expression profile in mouse myocardium after ischemia. Physiol Genomics 2: 93–100, 2000.—This study was designed to elaborate a molecular profile of expressed genes during ischemic injury to the mouse heart after surgical constriction of the left coronary artery without reperfusion. A mouse cDNA array containing 588 known genes was used to compare gene expression in heart RNA after 24-h ischemia with control tissue. Alterations in gene expression on the array were supported by relative reverse transcription-polymerase chain reaction analysis after timed periods of ischemia. Decreased levels of the cell cycle regulator p18ink4 and the oxidative responsive gene glutathione S-transferase were accompanied by an upregulation of the genes associated with cardiac muscle development, α-myosin heavy chain and fetal myosin alkali light chain. Other stress responses elicited by cardiac injury included an induction of Egr-1 and Egr-3 transcription factors, as well as the apoptotic regulator Bax. Altogether, these findings indicate that expression of genes associated with a fetal transcription program may be involved with the post ischemic remodeling process in heart ventricles.

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37

Ianuzzo, C. D., S. Brotherton, P. O'Brien, T. Salerno y M. H. Laughlin. "Myocardial biochemical and hemodynamic adaptations to chronic tachycardia". Journal of Applied Physiology 70, n.º 2 (1 de febrero de 1991): 907–13. http://dx.doi.org/10.1152/jappl.1991.70.2.907.

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The purpose was to determine the biochemical and hemodynamic adaptations of the myocardium to chronic tachycardia. Cardiac pacemakers were implanted in Yorkshire pigs and set at a rate of 180 beats/min for a period of 35-42 days. Animals were then anesthetized with pentobarbital sodium. Myocardial blood flow and hemodynamics were determined at three different heart rates (i.e., 120, 180, and 220 beats/min). Tissue samples were then taken for microsphere and biochemical analyses. Chronically paced hearts maintained better cardiac function and had consistently higher left ventricular blood flow with a higher endocardial-to-epicardial ratio. The activities of citrate synthase and 3-hydroxyacyl-CoA dehydrogenase were 23 and 45% greater in the paced hearts, respectively. The sarcoplasmic reticulum adenosinetriphosphatase activity was 55% greater in the paced hearts, whereas the myosin adenosinetriphosphatase was the same as in the control hearts. Polyacrylamide gels of the ventricular myosin isoforms showed only the V3 type to be present in both the control and paced hearts. These findings show that the heart of a large mammal adapts to chronic tachycardia (i.e., 180 beats/min) by elevating the aerobic and calcium-sequestering capacities without altering its myosin type.

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Dale, J. B. y E. H. Beachey. "Sequence of myosin-crossreactive epitopes of streptococcal M protein." Journal of Experimental Medicine 164, n.º 5 (1 de noviembre de 1986): 1785–90. http://dx.doi.org/10.1084/jem.164.5.1785.

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Group A streptococcal M proteins contain epitopes that crossreact with sarcolemmal membrane proteins of human myocardium and myosin. In the present study, synthetic peptide copies spanning the entire 197-residue pepsin extracted fragment of type 5 M protein were used to localize the myosin-crossreactive epitopes of the molecule. Peptide 84-116 inhibited by 75% the binding of myosin-crossreactive antibodies evoked by pep M5, as determined by ELISA. Immunoblot inhibition studies confirmed that peptide 84-116 almost totally inhibited the binding of pep M5 antibodies to the heavy chain of human cardiac myosin. None of the remaining synthetic peptides, including peptide 1-35, which contains protective epitopes, inhibited antibodies binding to myosin. Two of three rabbits immunized with peptide 84-116 developed low but significant levels of antibodies crossreactive with myosin. Identification of the primary structures containing tissue-crossreactive as opposed to protective epitopes should not only allow the development of safe and effective M protein vaccines, but may also provide insights into the pathogenesis of rheumatic heart disease.

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39

Palmer, Bradley M., David E. Fishbaugher, Joachim P. Schmitt, Yuan Wang, Norman R. Alpert, Christine E. Seidman, J. G. Seidman, Peter VanBuren y David W. Maughan. "Differential cross-bridge kinetics of FHC myosin mutations R403Q and R453C in heterozygous mouse myocardium". American Journal of Physiology-Heart and Circulatory Physiology 287, n.º 1 (julio de 2004): H91—H99. http://dx.doi.org/10.1152/ajpheart.01015.2003.

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The kinetic effects of the cardiac myosin point mutations R403Q and R453C, which underlie lethal forms of familial hypertrophic cardiomyopathy (FHC), were assessed using isolated myosin and skinned strips taken from heterozygous (R403Q/+ and R453C/+) male mouse hearts. Compared with wild-type (WT) mice, actin-activated ATPase was increased by 38% in R403Q/+ and reduced by 45% in R453C/+, maximal velocity of regulated thin filament ( VRTF) in the in vitro motility assay was increased by 8% in R403Q/+ and was not different in R453C/+, myosin concentration at half-maximal VRTF was reduced by 30% in R403Q/+ and not different in R453C/+, and the characteristic frequency for oscillatory work production ( b frequency), determined by sinusoidal analysis in the skinned strip at maximal calcium activation, was 27% lower in R403Q/+ and 18% higher in R453C/+. The calcium sensitivity for isometric tension in the skinned strip was not different in R403Q/+ (pCa50 5.64 ± 0.02) and significantly enhanced in R453C/+ (5.82 ± 0.03) compared with WT (5.58 ± 0.02). We conclude that isolated myosin and skinned strips of R403Q/+ and R453C/+ myocardium show marked differences in cross-bridge kinetic parameters and in calcium sensitivity of force production that indicate different functional roles associated with the location of each point mutation at the molecular level.

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40

Nassar, Rashid, Nadia N. Malouf, Lan Mao, Howard A. Rockman, Annette E. Oakeley, James R. Frye, J. René Herlong, Stephen P. Sanders y Page A. W. Anderson. "cTnT1, a cardiac troponin T isoform, decreases myofilament tension and affects the left ventricular pressure waveform". American Journal of Physiology-Heart and Circulatory Physiology 288, n.º 3 (marzo de 2005): H1147—H1156. http://dx.doi.org/10.1152/ajpheart.00140.2004.

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Four isoforms of cardiac troponin T (cTnT), a protein essential for calcium-dependent myocardial force development, are expressed in the human; they differ in charge and length. Their expression is regulated developmentally and is affected by disease states. Human cTnT (hcTnT) isoform effects have been examined in reconstituted myofilaments. In this study, we evaluated the modulatory effects of overexpressing one cTnT isoform on in vitro and in vivo myocardial function. A hcTnT isoform, hcTnT1, expressed during development and in heart disease but not in the normal adult heart, was expressed in transgenic (TG) mice (1–30% of total cTnT). Maximal active tension measured in skinned myocardium decreased as a function of relative hcTnT1 expression. The pCa at half-maximal force development, Hill coefficient, and rate of redevelopment of force did not change significantly with hcTnT1 expression. In vivo maximum rates of rise and fall of left ventricular pressure decreased, and the half-time of isovolumic relaxation increased, with hcTnT1 expression. Substituting total cTnT charge for hcTnT1 expression resulted in similar conclusions. Morphometric analysis and electron microscopy revealed no differences between wild-type (non-TG) and TG myocardium. No differences in isoform expression of tropomyosin, myosin heavy chain, essential and regulatory myosin light chains (MLC), TnI, or in posttranslational modifications of mouse cTnT, cTnI, or regulatory MLC were observed. These results support the hypothesis that cTnT isoform amino-terminal differences affect myofilament function and suggest that hcTnT1 expression levels present during human development and in human heart disease can affect in vivo ventricular function.

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Palaniyandi, Suresh S., Yusuke Nagai, Kenichi Watanabe, Meilei Ma, Punniyakoti T. Veeraveedu, Paras Prakash, Fadia A. Kamal et al. "Chymase Inhibition Reduces the Progression to Heart Failure After Autoimmune Myocarditis in Rats". Experimental Biology and Medicine 232, n.º 9 (octubre de 2007): 1213–21. http://dx.doi.org/10.3181/0703-rm-85.

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Chymase has been known as a local angiotensin II–generating enzyme in the cardiovascular system in dogs, monkeys, hamsters, and humans; however, recently it was reported that chymase also has various other functions. Therefore, we decided to examine whether the inhibition of chymase improves disease conditions associated with the pathophysiology of dilated cardiomyopathy in rats and its possible mechanism of action as rat chymase is unable to produce angiotensin II. We examined the effect of TY-51469, a novel chymase inhibitor (0.1 mg/kg/day [group CYI-0.1, n = 15] and 1 mg/kg/day [group CYI-1, n = 15]), in myosin-immunized postmyocarditis rats. Another group of myosin-immunized rats was treated with vehicle (group V, n = 15). Age-matched normal rats without immunization (group N, n = 10) were also included in the study. After 4 weeks of treatment, we evaluated cardiac function; area of fibrosis; fibrogenesis; levels of transforming growth factor (TGF)-β1 and collagen III; hypertrophy and its marker, atrial natriuretic peptide (ANP); and mast cell activity. Survival rate and myocardial functions improved dose-dependently with chymase inhibitor treatment after myosin immunization. A reduction in the percent area of myocardial fibrosis, fibrogenesis, myocardial hypertrophy, and mast cell activity along with a reduction in TGF-β1, collagen III, and ANP levels in the myocardium were noted in postmyocarditis rats that received chymase inhibitor treatment. The treatment also decreased myocardial aldosterone synthase levels in those animals. Inhibition of chymase reduces the pathogenesis of postmyocarditis dilated cardiomyopathy and progression to heart failure by preventing the pathological remodeling and residual inflammation in rats.

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42

Colson, Brett A., Tanya Bekyarova, Daniel P. Fitzsimons, Thomas C. Irving y Richard L. Moss. "Radial displacement of myosin cross-bridges in mouse myocardium due to ablation of myosin binding protein-C". Journal of Molecular and Cellular Cardiology 42, n.º 6 (junio de 2007): S118. http://dx.doi.org/10.1016/j.yjmcc.2007.03.272.

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43

Colson, Brett A., Tanya Bekyarova, Daniel P. Fitzsimons, Thomas C. Irving y Richard L. Moss. "Radial Displacement of Myosin Cross-bridges in Mouse Myocardium due to Ablation of Myosin Binding Protein-C". Journal of Molecular Biology 367, n.º 1 (marzo de 2007): 36–41. http://dx.doi.org/10.1016/j.jmb.2006.12.063.

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44

Gresham, Kenneth S., Ranganath Mamidi, Jiayang Li, Hyerin Kwak y Julian E. Stelzer. "Sarcomeric protein modification during adrenergic stress enhances cross-bridge kinetics and cardiac output". Journal of Applied Physiology 122, n.º 3 (1 de marzo de 2017): 520–30. http://dx.doi.org/10.1152/japplphysiol.00306.2016.

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Molecular adaptations to chronic neurohormonal stress, including sarcomeric protein cleavage and phosphorylation, provide a mechanism to increase ventricular contractility and enhance cardiac output, yet the link between sarcomeric protein modifications and changes in myocardial function remains unclear. To examine the effects of neurohormonal stress on posttranslational modifications of sarcomeric proteins, mice were administered combined α- and β-adrenergic receptor agonists (isoproterenol and phenylephrine, IPE) for 14 days using implantable osmotic pumps. In addition to significant cardiac hypertrophy and increased maximal ventricular pressure, IPE treatment accelerated pressure development and relaxation (74% increase in dP/d tmax and 14% decrease in τ), resulting in a 52% increase in cardiac output compared with saline (SAL)-treated mice. Accelerated pressure development was maintained when accounting for changes in heart rate and preload, suggesting that myocardial adaptations contribute to enhanced ventricular contractility. Ventricular myocardium isolated from IPE-treated mice displayed a significant reduction in troponin I (TnI) and myosin-binding protein C (MyBP-C) expression and a concomitant increase in the phosphorylation levels of the remaining TnI and MyBP-C protein compared with myocardium isolated from saline-treated control mice. Skinned myocardium isolated from IPE-treated mice displayed a significant acceleration in the rate of cross-bridge (XB) detachment (46% increase) and an enhanced magnitude of XB recruitment (43% increase) at submaximal Ca2+ activation compared with SAL-treated mice but unaltered myofilament Ca2+ sensitivity of force generation. These findings demonstrate that sarcomeric protein modifications during neurohormonal stress are molecular adaptations that enhance in vivo ventricular contractility through accelerated XB kinetics to increase cardiac output. NEW & NOTEWORTHY Posttranslational modifications to sarcomeric regulatory proteins provide a mechanism to modulate cardiac function in response to stress. In this study, we demonstrate that neurohormonal stress produces modifications to myosin-binding protein C and troponin I, including a reduction in protein expression within the sarcomere and increased phosphorylation of the remaining protein, which serve to enhance cross-bridge kinetics and increase cardiac output. These findings highlight the importance of sarcomeric regulatory protein modifications in modulating ventricular function during cardiac stress.

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45

Vornanen, M. "Seasonal and temperature-induced changes in myosin heavy chain composition of crucian carp hearts". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 267, n.º 6 (1 de diciembre de 1994): R1567—R1573. http://dx.doi.org/10.1152/ajpregu.1994.267.6.r1567.

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Myosin heavy chain isoforms of the ventricular myocardium from crucian carp (Carassius carassius L.) hearts were analyzed in different times of the year by gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis [K. A. Esser, M. O. Boluyt, and T. P. White, Am. J. Physiol. 255 (Heart Circ. Physiol. 24): H659-H663, 1988]. In winter only one myosin heavy chain type was present, but in summer about one-half of the winter myosin was replaced by more slowly moving summer myosin. The occurrence of summer myosin correlated with seasonal changes in water temperature of the pond, where the fish were caught. Furthermore, the heavy chain composition of the heart was altered by temperature acclimation in the laboratory: cold-acclimated (2 degrees C) fish had only winter myosin, but warm-acclimated (22 degrees C) fish had both summer and winter myosin in about equal amounts. Myosin adenosinetriphosphatase activity of the hearts containing both summer and winter myosin was higher than that of hearts containing only winter myosin. Functionally, changes in myosin heavy chain composition were associated with inverse thermal acclimation in the heart rate. Warm-acclimated fish had higher in vitro heart rate and shorter contraction duration than cold-acclimated animals. Present findings suggest that changes in myosin heavy chain composition together with concomitant changes in Ca2+ activation of contraction make possible large seasonal alterations in the activity of crucian carp hearts. These adjustments are needed to adapt the cardiovascular system to winter hibernation and summer activity, which are dictated by seasonally bound changes in environmental conditions.

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46

Min, Jiang-Yong, Yinke Yang, Kimber L. Converso, Lixin Liu, Qin Huang, James P. Morgan y Yong-Fu Xiao. "Transplantation of embryonic stem cells improves cardiac function in postinfarcted rats". Journal of Applied Physiology 92, n.º 1 (1 de enero de 2002): 288–96. http://dx.doi.org/10.1152/jappl.2002.92.1.288.

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Massive loss of cardiac myocytes after myocardial infarction (MI) is a common cause of heart failure. The present study was designed to investigate the improvement of cardiac function in MI rats after embryonic stem (ES) cell transplantation. MI in rats was induced by ligation of the left anterior descending coronary artery. Cultured ES cells used for cell transplantation were transfected with the marker green fluorescent protein (GFP). Animals in the treated group received intramyocardial injection of ES cells in injured myocardium. Compared with the MI control group injected with an equivalent volume of the cell-free medium, cardiac function in ES cell-implanted MI animals was significantly improved 6 wk after cell transplantation. The characteristic phenotype of engrafted ES cells was identified in implanted myocardium by strong positive staining to sarcomeric α-actin, cardiac α-myosin heavy chain, and troponin I. GFP-positive cells in myocardium sectioned from MI hearts confirmed the survival and differentiation of engrafted cells. In addition, single cells isolated from cell-transplanted MI hearts showed rod-shaped GFP-positive myocytes with typical striations. The present data demonstrate that ES cell transplantation is a feasible and novel approach to improve ventricular function in infarcted failing hearts.

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47

Stelzer, Julian E., Jitandrakumar R. Patel, M. Charlotte Olsson, Daniel P. Fitzsimons, Leslie A. Leinwand y Richard L. Moss. "Expression of cardiac troponin T with COOH-terminal truncation accelerates cross-bridge interaction kinetics in mouse myocardium". American Journal of Physiology-Heart and Circulatory Physiology 287, n.º 4 (octubre de 2004): H1756—H1761. http://dx.doi.org/10.1152/ajpheart.00172.2004.

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Transgenic mice expressing an allele of cardiac troponin T (cTnT) with a COOH-terminal truncation (cTnTtrunc) exhibit severe diastolic and mild systolic dysfunction. We tested the hypothesis that contractile dysfunction in myocardium expressing low levels of cTnTtrunc (i.e., <5%) is due to slowed cross-bridge kinetics and reduced thin filament activation as a consequence of reduced cross-bridge binding. We measured the Ca2+ sensitivity of force development [pCa for half-maximal tension generation (pCa50)] and the rate constant of force redevelopment ( ktr) in cTnTtrunc and wild-type (WT) skinned myocardium both in the absence and in the presence of a strong-binding, non-force-generating derivative of myosin subfragment-1 (NEM-S1). Compared with WT mice, cTnTtrunc mice exhibited greater pCa50, reduced steepness of the force-pCa relationship [Hill coefficient ( nH)], and faster ktr at submaximal Ca2+ concentration ([Ca2+]), i.e., reduced activation dependence of ktr. Treatment with NEM-S1 elicited similar increases in pCa50 and similar reductions in nH in WT and cTnTtrunc myocardium but elicited greater increases in ktr at submaximal activation in cTnTtrunc myocardium. Contrary to our initial hypothesis, cTnTtrunc appears to enhance thin filament activation in myocardium, which is manifested as significant increases in Ca2+-activated force and the rate of cross-bridge attachment at submaximal [Ca2+]. Although these mechanisms would not be expected to depress systolic function per se in cTnTtrunc hearts, they would account for slowed rates of myocardial relaxation during early diastole.

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48

YOSHIDA, Ken-ichi, Tohru HANAFUSA, Ryoji MATOBA y Choei WAKASUGI. "Proteolysis of myosin and troponin in human myocardium of elderly subjects." Japanese Heart Journal 31, n.º 5 (1990): 683–91. http://dx.doi.org/10.1536/ihj.31.683.

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49

Turcani, Marian, Dirk Thormaehlen y Heinz Rupp. "Tedisamil attenuates foetal transformation of myosin in the hypertrophied rat myocardium". British Journal of Pharmacology 143, n.º 5 (noviembre de 2004): 561–72. http://dx.doi.org/10.1038/sj.bjp.0705992.

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50

Li Shaowei y Yang Tongshu. "Analysis of myosin light chains in myocardium from Keshan disease patients". Journal of Molecular and Cellular Cardiology 24 (mayo de 1992): 222. http://dx.doi.org/10.1016/0022-2828(92)90690-2.

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