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Skeletal Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
As in most cells, ATP is the energy source that is immediately available to fuel cell activity – in this case, muscle contraction. However, the number of ATP molecules required for even moderate muscle activity can be enormous. The contraction of a single thick filament may involve the hydrolysis of a few thousand ATP molecules per second, and a muscle may contain tens of billions of thick filaments. The ATP immediately available can only sustain about 10 twitches or so. More ATP is readily available in the form of creatine phosphate (CP), also known as phosphorylcreatine. Creatine is a small molecule that is produced from three amino acids (L-arginine, glycine, and L-methionine), mainly in the liver and kidneys, and transported by the blood for use by various cells including muscle. Creatine undergoes in muscle the following reversible reaction that is catalyzed by the enzyme creatine phosphokinase (CPK):
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
Cardiac muscle action potentials trigger myocardial muscle contraction by a process called excitation–contraction coupling, which involves the interaction of actin and myosin filaments as a result of a dramatic increase in intracellular free calcium (from 0.1 to 100 μM). The thick filament is made up of myosin, a protein consisting of a tail and two globular heads, each of which has an ATP binding site and an actin binding site. The thin filament consists of actin, which interacts with the heads of myosin molecules to form cross-bridges with the thick filaments, and two regulatory proteins, tropomyosin (which lies in a groove of the actin α-helix) and troponin.
Cellular Regulation of Myometrial Contractility and Essentials of Tocolytic therapy
Published in Gabor Huszar, The Physiology and Biochemistry of the Uterus in Pregnancy and Labor, 2020
Other differences are related to the structure of the actin and myosin filaments (Figure 2). In skeletal muscles the actin filaments originate in each Z-line and point toward the center of the sarcomere. The myosin filaments are also bidirectional; the myosin molecules are laid down from the center of the sarcomere toward the Z-lines. Thus, in skeletal muscles the thick and thin filaments are interrupted, and the bidirectional configuration repeats itself in each sarcomere. In smooth muscles the myosin molecules are aligned in the same direction and form long, uninterrupted filaments. This unidirectional polarity enables actin to interact with myosins along the entire length of the thick filament, which explains the severalfold greater shortening ability of smooth muscles compared to skeletal muscles.
Current and emerging pharmacotherapy for the management of hypertrophic cardiomyopathy
Published in Expert Opinion on Pharmacotherapy, 2023
Akiva Rosenzveig, Neil Garg, Shiavax J. Rao, Amreen K. Kanwal, Arjun Kanwal, Wilbert S. Aronow, Matthew W. Martinez
The essential unit of contraction in cardiac myocytes is the sarcomere [20]. Myosin is the molecular motor of the sarcomere that hydrolyzes adenosine triphosphate (ATP) to interact with the thin filament actin. However, for every given contraction, only 10% of myosin molecules are utilized to generate force [21], thus preventing unnecessary energy utilization. During relaxation, paired myosin head domains can interact in either a super relaxed state (SRX), where neither head can interact with actin filaments, or in a disordered state (DRX), where one myosin head is free to hydrolyze ATP and interacts with actin [22]. The predominant myosin isoform, MYH7 (B-myosin heavy chain), and myosin-binding protein C (MYBPC) harbor most of the pathogenic variants in HCM [23]. These pathologic variants increase the proportion of myosin heads in DRX leading to hypercontractility and increased energy expenditure [22]. In these individuals, hypercontractility and impaired diastolic function precede left ventricular hypertrophy [24,25].
Early clinical and pre-clinical therapy development in Nemaline myopathy
Published in Expert Opinion on Therapeutic Targets, 2022
Gemma Fisher, Laurane Mackels, Theodora Markati, Anna Sarkozy, Julien Ochala, Heinz Jungbluth, Sithara Ramdas, Laurent Servais
Nemaline rods that are seen on Gömöri trichome staining are the histological hallmark of NM. The rods are located in proximity to Z-lines and are considered to be derived from proteins involved in Z-line assembly and maintenance [16,25]. Both Z-lines and rods have a similar lattice structure and comprise similar proteins, which include α-actinin, actin, tropomyosin, myotilin, γ-filamin, cofilin-2, telethonin and nebulin [16,25]. The precise mechanisms of formation are uncertain, although they have been noted to occur in metabolic conditions (Complex 1 deficiency [26]), certain infections [4], inflammatory conditions [27] and with some drugs (e.g. Zidovudine [28])[29]. Nemaline rods are, however, likely to be an epiphenomenon that does not explain all of the pathological mechanisms of NM [16]. Other relevant mechanisms include altered thin filament calcium sensitivity and impaired thick and thin filament interactions resulting in an excitation-contraction disturbance, as well as more general disturbances in thin filament protein turnover [7,30].
Effect of nebivolol on altered skeletal and cardiac muscles induced by dyslipidemia in rats: impact on oxidative and inflammatory machineries
Published in Archives of Physiology and Biochemistry, 2022
Ghada Farouk Soliman, Omnia Mohamed Abdel-Maksoud, Mohamed Mansour Khalifa, Laila Ahmed Rashed, Walaa Ibrahim, Heba Morsi, Hanan Abdallah, Nermeen Bastawy
Reactive oxygen species (ROS) are important for the regulation of several body functions (Di Meo et al.2016). They are generated in skeletal muscles both during rest and contraction (Powers et al.2011). Mitochondria are major sources of ROS within the striated muscle cell (Görlach et al.2015). The skeletal muscles contain abundant antioxidant Defence system to protect against changes in the redox state. Data exist regarding the deleterious effects of oxidative stress within striated muscle tissues at several levels including cell membrane, sarcoplasmic reticulum, up to myofibrils (Powers et al.2011). Thin filament protein oxidation negatively affects contractile function in striated muscles by reducing calcium sensitivity of the myofilament (Lamb and Westerblad 2011, Steinberg 2013). Changes may occur in titin as a result of oxidative stress in striated muscles (Beckendorf and Linke 2015). Superoxide generated within striated muscle fibres causes oxidation of the ryanodine receptor and, thus, interferes with calcium release (Cherednichenko et al.2004, Xia et al.2003). Glutathione (GSH) is a hydrogen donor formed mainly in the liver, and its reduced form plays important roles in reducing H2O2 and some other cellular antioxidants (Powers et al.2011, Di Meo et al.2016). In addition to diminished expression of cardiac antioxidant enzymes with resultant oxidative stress by the effect of hypercholesterolaemia (Csonka et al.2016).