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Skeletal Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The other system is the sarcoplasmic reticulum (SR), which is analogous to the endoplasmic reticulum of other cells (Section 1.1). The SR consists of a network of tubes or channels that run mostly longitudinally around each myofibril. The SR channels enlarge in the vicinity of the T tubules to form chambers, or terminal cisternae, whose membrane is in close apposition to that of the T tubule. The combination of a T tubule and the two terminal cisternae on either side is a triad.
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
Within the myocyte, myofibrils are surrounded by a network of membranes, the sarcoplasmic reticulum. The sarcoplasmic reticulum in the heart is less dense and not as well developed as that in skeletal muscles. The T-tubules of the cardiac muscle are located at the Z lines, whereas they are positioned at the ends of the I-bands in skeletal muscle. Consequently, the T-tubule is linked with the terminal cisterna of the sarcoplasmic reticulum of only one sarcomere, forming a diad, rather than a triad, in the skeletal muscle. As there is less sarcoplasmic reticulum in cardiac muscle, intracellular calcium levels depend on calcium influx into the cardiac myocyte through L-type calcium channels on the sarcolemma (via activated dihydropyridine receptor), as well as its release from sarcoplasmic reticulum. The L-calcium channels open more slowly than sodium channels and remain open longer (200–300 ms). This explains why the action potential in ventricular muscle is much longer than in skeletal muscle in which the L-type calcium channels do not open. Some of this calcium causes opening of ryanodine receptors on the sarcoplasmic reticulum, and calcium diffuses out of the sarcoplasmic reticulum. All the calcium released from the sarcoplasmic reticulum, and some from the influx via the sarcolemma, binds to troponin, resulting in actin–myosin interaction and cross-bridge cycling.
Skeletal Muscle
Published in Manoj Ramachandran, Tom Nunn, Basic Orthopaedic Sciences, 2018
Mike Fox, Steve Key, Simon Lambert
Surrounding each myofibril is an intracytoplasmic membranous sac called the sarcoplasmic reticulum (Figure 12.4). This membrane serves as a repository for calcium, which is released to stimulate contraction. It forms terminal cisternae where it is adjacent to the transverse (T)-tubules. Ryanodine receptors on the terminal cisternae are the calcium channels that are opened by mechanical conformational change through their connection to T-tubule membrane proteins.
Effects of Trans-Cinnamaldehyde on Reperfused Ischemic Skeletal Muscle and the Relationship to Laminin
Published in Journal of Investigative Surgery, 2021
Esra Pekoglu, Belgin Buyukakilli, Cagatay Han Turkseven, Ebru Balli, Gulsen Bayrak, Burak Cimen, Senay Balci
In our study, we observed that in the I-R group the force generation in EDL muscles decreased and SR cells expanded. Since the terminal cisterna provides rapid calcium delivery, it is well developed in fast contracting muscles such as EDL. Ca2+ release from terminal cisternae initiates contraction processes. Therefore, as seen in our study, expansion of muscle cells in SR cisterns in the I-R groups can disrupt Ca2+ release from SR and reduce force production. SR cisterna expansion of muscle cells may have been caused by I-R-induced free radical formation. Other studies have also described a reduction in muscle force generation due to acute I-R injury [32,33]. Loss in muscle force generation; it may be due to disruption of excitation-contraction coupling, separation and/or loss of proteins involved in the formation and transmission of force, and the rise in non-contractile components in muscle tissue [18].
Emerging proteomic biomarkers of X-linked muscular dystrophy
Published in Expert Review of Molecular Diagnostics, 2019
Paul Dowling, Sandra Murphy, Margit Zweyer, Maren Raucamp, Dieter Swandulla, Kay Ohlendieck
The majority of comparative proteomic analyses of dystrophic skeletal muscle tissues has shown a greater number of increased versus decreased protein species, which is probably due to the occurrence of degeneration/regeneration cycle in the absence of dystrophin. Overlapping proteomic hits suggest that a variety of skeletal muscle-associated proteins are suitable candidates for the establishment of a biomarker signature of X-linked muscular dystrophy. This includes marker proteins involved in fibre contraction, energy metabolism, cytoskeletal maintenance, the cellular stress response and ion homeostasis (Table 2). The initial gel-based proteomic screening of mdx-23 skeletal muscles identified a decreased concentration of adenylate kinase isoform AK1 [48], which was confirmed by several studies using both two-dimensional gel electrophoresis and liquid chromatography [50–52,56,59]. Lower levels of adenylate kinase may be linked to abnormal nucleotide metabolism in muscular dystrophy [50]. Another striking characteristic of dystrophic fibres are decreased levels of the cytosolic Ca2+-binding protein regucalcin [51,52] and the luminal Ca2+-sequestering proteins calsequestrin of the terminal cisternae region and sarcalumenin of the longitudinal tubules [45,49,61,64]. Changes in theses abundant Ca2+-binding proteins were identified in both the highly fibrotic diaphragm and less severely affected leg muscles, indicating a general role in the molecular pathogenesis of dystrophinopathy. The enhanced susceptibility of dystrophin-lacking muscle fibres to micro-rupturing of the fragile sarcolemma causes an increased influx of Ca2+-ions, which in turn results in higher levels of proteolytic degradation [16]. The additional impairment of efficient Ca2+-buffering in the cytosol and lumen of the sarcoplasmic reticulum appears to exacerbate these physiological disturbances of excitation-contraction coupling in muscular dystrophy [49].