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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
The tubular system of skeletal muscle fibers consists of two primary parts, the sarcoplasmic reticulum (SR) and the TT system. The SR is analogous to the smooth endoplasmic reticulum in non-muscle cells and as a network that runs longitudinally down the fiber, parallel to the myofibrils and surrounds them. The SR consists of a longitudinal portion (LTP) containing a Ca++-ATPase (ATP using) pump and is connected to saclike terminal cisterna (TC) at either end of the longitudinal portion (Figure 1.8a). During a fiber contraction, the longitudinalportion becomes shorter and wider. The pump in the LTP directs Ca++ into the TC where they are stored. Side channels allow the SR to interconnect with rest of the SR throughout the cell; thus, forming a giant tubular network (125, 127). The SR acts as a Ca++ reservoir (TC). Under normal resting conditions, compared to the surrounding sarcoplasm the concentration of Ca++ in the TC is about 10,000 times higher (20). As a result of depolarization, Ca++are released through RYR channels into the sarcoplasm, markedly increasing the sarcoplasmic Ca++ concentration. The increased Ca++ concentration is necessary for muscle contraction activation (192). With the removal of depolarization, re-segregation of Ca++ into the SR results in muscle relaxation.
Pharmacological Management of Amyotrophic Lateral Sclerosis
Published in Sahab Uddin, Rashid Mamunur, Advances in Neuropharmacology, 2020
Shalini Mani, Chahat Kubba, Tanya Sharma, Manisha Singh
Thirdly, tirasemtiv activates the complex of troponin, present in fast-twitch skeletal muscle fibers to presence of calcium (Hwee et al., 2014). A demonstrable mechanism of action is advancement in the muscle tightening as a reaction to decreased neural participation thus significantly diminishing muscle weariness (Shefner et al., 2012). A good number of trials on human were performed in ALS patients because the wasting in muscle is a sign of ALS (Shefner et al., 2013). The, recruiting total 605 patients was a failure on the main endpoint (Shefner et al., 2016). As the research had shown the statistical importance on main two secondary endpoints, thus these researchers offer the probability to effectively initiate further Phase 3 study.
Collection and Expansion of Stem Cells
Published in Richard K. Burt, Alberto M. Marmont, Stem Cell Therapy for Autoimmune Disease, 2019
Normal repair and regeneration of skeletal muscle fibers occurs following injury from muscle satellite cell activation, proliferation and migration to the site of injury.164 Satellite cells are a unique population of usually quiescent cells located outside of the myofiber, between the sarcolemma and the covering basement membrane, and account for approximately 5% of the nuclei present in muscle fibers. When activated, satellite cells have the capacity to divide extensively in order to produce sufficient myoblasts to replace damaged muscle fiber. Recovery of satellite cells via standard tissue dissociation techniques, fail to extract more that 99% of the known myogenic population of mature muscle,165 bringing into question the number of cell types that contribute to muscle development in vivo. Satellite cells attached to muscle fibers are capable of rapid proliferation and myogenesis in tissue culture,165 but when transplanted in vivo into recipient murine muscle, the majority of cultured cells undergo rapid necrotic cell death.166 Only a few cells survive to give rise to regenerated myofibers and satellite cells. More stringent techniques for identifying myogenic precursors within muscle and tracing their fate are required to determine the spectrum of cell types responsible for skeletal muscle regeneration in vivo.
Prenatal Diagnosis of Isolated Right Ventricular Non-Compaction Cardiomyopathy with an MYH7 Likely Pathogenic Variant
Published in Fetal and Pediatric Pathology, 2023
Weiming Yu, Mary Ann Thomas, Lindsay Mills, James R. Wright
MYH7 (myosin heavy chain 7) is the most commonly associated gene in NVM [10]. The gene encodes β myosin heavy chain protein, which is expressed predominantly in normal human ventricle, and also expressed in type I skeletal muscle fibers. More than 200 mutations have been described in MYH7. Mutations are distributed throughout the gene but are predominantly clustered in the head region [11]. Pathogenic variants of MYH7 gene are considerably heterogeneous, different variants within the same sarcomere gene can result in both overlapping and divergent clinical manifestations. MYH7 mutations are associated with 13%-20% of cases of LVNC, 16% of cases of hypertrophic cardiomyopathy, 4%-5% cases of dilated cardiomyopathy, and also include myosin storage myopathy and Laing early-onset distal myopathy [11,17].
Emerging clinical investigational drugs for the treatment of amyotrophic lateral sclerosis
Published in Expert Opinion on Investigational Drugs, 2023
Loreto Martinez-Gonzalez, Ana Martinez
(NCT04944784, NCT05442775) belongs to a second generation of fast skeletal muscle troponin activators [115]. It is a drug intended to slow the rate of calcium release from the regulatory troponin complex of fast skeletal muscle fibers. By slowing the rate of calcium release, reldesemtiv sensitizes the sarcomere to calcium, leading to an increase in muscle contractility. In the phase II study, the analysis of the primary efficacy did not show statistical significance but tolerability was good [41,116]. Thus, a phase III trial is ongoing to reveal the impact of reldesemtiv on ALS patients. The trial COURAGE-ALS will enroll 555 ALS patients that will be randomized (2:1) to receive reldesemtiv or placebo for 24 weeks. In that point the effect of the drug versus placebo will be evaluated analyzing the ALSFRS-R scores.
Proteomic profiling of carbonic anhydrase CA3 in skeletal muscle
Published in Expert Review of Proteomics, 2021
Paul Dowling, Stephen Gargan, Margit Zweyer, Hemmen Sabir, Dieter Swandulla, Kay Ohlendieck
The muscular dystrophies are a large group of inherited disorders that primarily affect skeletal muscles [114]. X-linked muscular dystrophies are due to mutations in the DMD gene that encodes a variety of tissue-specific isoforms of the protein named dystrophin. Loss of the full-length dystrophin isoform Dp427-M causes the Duchenne type of muscular dystrophy, which is a highly progressive muscle wasting disorder of early childhood [115]. Dystrophin exists in skeletal muscles in a tight linkage with several sarcolemmal glycoproteins [116]. The core dystrophin-glycoprotein complex interacts with the basal lamina on the outside of muscle fibers and the actin membrane cytoskeleton on the inside of contractile cells forming a supramolecular membrane assembly. The dystrophin complex was shown to be involved in the integration of fiber stability, the transmission of lateral force to the extracellular matrix, the organization of the cytoskeletal network and cellular signaling events in the peripheral membrane system of skeletal muscle fibers [116].