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Electrical Properties of the Heart
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Tropomyosin consists of two α-helical chains and lies in the groove between the two actin polymers, preventing the interaction of myosin with actin – an effect modulated by troponin. The globular protein troponin is present with tropomyosin at regular intervals on the thin actin filaments, with one molecule of each for every seven actin monomers. There are three subunits: (i) troponin-C, which binds Ca++ ions during muscle activation and exposes the actin site for cross-bridge formation; (ii) troponin-T, which anchors the troponin complex to tropomyosin and (iii) troponin-I, which inhibits actin–myosin interaction at rest.
Energy Demand of Muscle Machines
Published in Peter W. Hochachka, Muscles as Molecular and Metabolic Machines, 2019
Ebashi first discovered that the effect of Ca++ on the interaction of actin and myosin is mediated by tropomyosin and the troponin complex, which are located in the thin filament and constitute about a third of its mass (Figures 4-1 and 4-5). Tropomyosin is a two-stranded α-helical rod. This highly elongated 70-kDa protein is aligned nearly parallel to the long axis of the thin filament. Troponin (Tn) is a complex of three polypeptide chains: TnC (18 kDa), Tnl (24 kDa), and TnT (37 kDa). TnC binds calcium ions, Tnl binds to actin, and TnT binds to tropomyosin. The troponin complex is located in the thin filaments at intervals of 385 Å, a period set by the length of tropomyosin. A troponin complex bound to a molecule of tropomyosin regulates the activity of about seven actin monomers (Murray and Weber, 1974).
The cardiac myocyte: excitation and contraction
Published in Neil Herring, David J. Paterson, Levick's Introduction to Cardiovascular Physiology, 2018
Neil Herring, David J. Paterson
The thin actin filament is 1.05 μm long × 6 nm wide. Actin filaments are interposed between the myosin fila-ments, with one end free in the A band and the other rooted in the Z line. The actin filaments form the pale I (isotropic) band. The I band is only ~0.25 μm wide, because most of the actin filament is in the space between the myosin filaments, in the A band. In other words, the actin and myosin fila-ments interdigitate. The filamentous actin (F-actin) is a poly-mer of globular actin subunits (G‑actin), which are bonded side-by-side. The thin filament consists of two such F-actin strings, arranged as a two-stranded helix (Figure 3.3). The groove of the double helix contains a regulatory protein, tropomyosin. Also, a regulatory complex composed of tro-ponins is attached to the tropomyosin and actin at regular intervals. The tropomyosin–troponin complex plays a key role in initiating contraction.
LC-MS/MS: A sensitive and selective analytical technique to detect COVID-19 protein biomarkers in the early disease stage
Published in Expert Review of Proteomics, 2023
Siva Nageswara Rao Gajula, Ankita Sahebrao Khairnar, Pallavi Jock, Nikita Kumari, Kendre Pratima, Vijay Munjal, Pavan Kalan, Rajesh Sonti
Troponin C, troponin1, and troponin T are three regulatory proteins that form the troponin complex and are essential for skeletal and cardiac muscle contraction. Cardiac troponin is a prognostic and diagnostic biomarker in acute coronary syndrome and myocardial infarction [115,116]. Many investigations manifest that COVID-19 patients with heart diseases such as myocardial infarction have a higher mortality rate attributed to elevated cardiac troponin levels [117–120]. Shi et al. demonstrated that among 416 COVID-19 patients, 1 in 5 had elevated cardiac troponin levels [120]. Furthermore, recent studies have shown that cardiac troponin is higher in critically ill and non-survivor patients than in infected patients [121,122]. Schneck et al. developed a selective and sensitive LC-MS/MS method for detecting and quantifying cardiac troponin I in human plasma using targeted mass spectrometry [123].
MiR-33a-5p targets NOMO1 to modulate human cardiomyocyte progenitor cells proliferation and differentiation and apoptosis
Published in Journal of Receptors and Signal Transduction, 2021
Wang Xing, Tiangang Li, Yixuan Wang, Yi Qiang, Chencheng Ai, Hanbo Tang
Transcription factor GATA4 has become a the nuclear effector of several cardiac signaling pathways that regulate critical cardiac cascades through post-translational modifications and protein-protein interactions [30], and deletion of GATA4 from mesodermal progenitors during early development would lead to absence of cardiomyocytes [31]. Troponin T (TnT), the tropomyosin-binding and thin filament anchoring subunit, of the troponin complex in regulating of muscle contraction [32]. Cardiac troponin T (cTnT) is considered to be a reliable biomarker of myocardial injury in humans [33]. And during the differentiation process of cardiomyocytes, cTnT expression was increased [34]. Myocyte enhancer factor2C (MEF2C) is a member of the MEF2 family, functions as a key role in activating cardiac-specific embryonic genes expressions [35]. It was worth noting that expressions of GATA4, cTnT and MEF2C were down-regulated by up-regualtion of miR-33a-5p in the present study, indicating that degree of hCMPCs differentiation into cardiomyocytes was inhibited by up-regulation of miR-33a-5p.
An update on the use and discovery of prognostic biomarkers in acute decompensated heart failure
Published in Expert Review of Molecular Diagnostics, 2019
Douglas Darden, Marin Nishimura, Justin Sharim, Alan Maisel
Typically assumed to be a biomarker of myonecrosis, cardiac troponin (cTn) has been traditionally used for the diagnosis of acute myocardial infarction, however troponin can also be elevated in other disorders and used as an aid in prognosis. The troponin complex consists of subunits C, T, and I, and plays a vital role in the actin-myosin interaction. Of the three, troponin T (cTnT) and troponin I (cTnI) are relatively specific to cardiomyocytes. In addition to acute MI or type I MI, several other non-coronary pathologies cause a cTn release (type 2 MI), such as arrhythmias, respiratory failure, and heart failure [53]. Furthermore, the Food and Drug Administration (FDA) recently approved the use of the first high sensitivity cTn (hs-cTn) assay in the United States [32]. These highly sensitivity assays, by definition, are designed to be able to detect cTn in greater than 50% of healthy subject [54].