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Neuromuscular Physiology
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
Actin molecules exists in a globular form (G-actin), which is made of a single peptide chain and a filamentous form (F-actin) (Figure 1.11a). Actin filaments (F-actin) result from the polymerization of G-actin monomers. F-actin myofilaments consist of two G-actin polymers wrapped around each other, creating a double helix with a 360 Α period, and form the thin filaments of the sarcomere. Each actin myofilament contains about 350 G-actin molecules. In solution, actin and myosin bind, forming actinomyosin, strands of which will contract in the presence of ATP (127).
Carrier Screening For Inherited Genetic Conditions
Published in Vincenzo Berghella, Obstetric Evidence Based Guidelines, 2022
Whitney Bender, Lorraine Dugoff
Clinical features: This disease causes disorganization of the proteins found in sarcomeres in skeletal muscles and is the most common congenital myopathy. There are different types based on the degree of severity. Proximal muscle weakness is the most common and may worsen over time.
Striated MusclesSkeletal and Cardiac Muscles
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
Skeletal muscle fibres are 10–100 μm in diameter, as long as the muscle itself, and have multiple nuclei on the periphery of the cell. Each fibre comprises many myofibrils surrounded by cytoplasm containing mitochondria, the internal membranes of the sarcoplasmic reticulum and the T-tubules and glycogen. The striated pattern observed under light microscopy is formed by the regular organization of interdigitating thick myosin and thin actin filaments in the myofibrils (Figure 12.1). The sarcomere is the basic unit of muscle contraction and is enclosed by adjacent Z lines.
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].
Circadian regulation of cardiac muscle function and protein degradation
Published in Chronobiology International, 2023
Proteostasis, including protein synthesis, processing/folding and degradation, is an important cellular mechanism in cardiac muscles (Henning and Brundel 2017; McLendon and Robbins 2015). Compared with non-muscle cells, cardiac muscles are terminally differentiated, must contract throughout lifetime, require robust metabolic/stress responses and involve specialized cellular machineries for electric conductance. The structural and functional unit of striated muscles, including both cardiac and skeletal muscles, is the sarcomere (Martin and Kirk 2020; Ono 2010), which is highly conserved throughout from worms to mammals. Sarcomeres line up sequentially, and tied together by a complex protein assembly called Z-disc to form contractible myofibrils, which in turn are bound in bundles to form cardiomyocytes. The sarcomere consists mainly of the myosin thick filaments and actin thin filaments, with a large number of associated structural and regulatory proteins. Given the heart is the first organ to be formed after birth and must continuously function until death, and that cardiomyocytes are post-mitotic, protein quality control at the sarcomere plays a particularly important role in cardiac proteostasis (Henning and Brundel 2017; Martin and Kirk 2020). Of particular importance is protein degradation mechanisms to remove misfolded or faulty proteins.
Multi-modality management of hypertrophic cardiomyopathy
Published in Hospital Practice, 2023
Shiavax J. Rao, Shaikh B. Iqbal, Arjun S. Kanwal, Wilbert S. Aronow, Srihari S. Naidu
Myosin, the protein that propels the sarcomere and drives muscle contraction, equilibrates between a super relaxed state (with low adenosine triphosphatase [ATPase] activity) and a disordered relaxed state (allowing for interaction with actin) [54]. HCM is characterized by impairment in the energetic and mechanical properties of cardiac myocytes, with recent experimental data suggesting that the resultant hyperdynamic contractility and impaired myocardial relaxation may be due to an imbalance and shift of myosin toward the disordered relaxed state [55–60]. Given these insights, with current limitations of conventional pharmacotherapies and a relatively high threshold for invasive therapies, molecules decreasing the ATPase activity of myosin have emerged as pharmacotherapeutic options targeting the critical pathophysiological mechanism of disease in HCM [61,62].