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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
The sarcoplasmic reticulum is a network of vesicular elements running longitudinally around the myofibrils. The sarcoplasmic reticulum sequesters calcium by a calcium- and magnesium-dependent ATPase pump. At regular places on the myofibril (A–I junction in most muscles), T-tubules, invaginations of the muscle membrane, form triad structures with two lateral sacs of the sarcoplasmic reticulum. The T-tubules and adjacent sarcoplasmic reticulum form electron-dense feet, although their lumina are not connected. The muscle action potential propagates down the T system, opening sarcoplasmic reticulum calcium-release channels, enabling contraction.
Muscle
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
When the action potentials in the alpha motor neuron cease, stimulation of the muscle fiber is ended. The Ca++ ions are actively pumped back into the sarcoplasmic reticulum and, troponin and tropomyosin return to their original positions, resulting in the myosin binding sites on the actin being covered once again. The thin filaments return passively to their original positions, resulting in muscle relaxation.
Anatomy and Physiology of the Autonomic Nervous System
Published in Kenneth J. Broadley, Autonomic Pharmacology, 2017
Smooth muscle contraction is thought to occur in a similar fashion to that in skeletal muscle, although at a slower rate, probably because of a reduced availability of ATP as an energy source. According to the sliding-filament theory, actin and myosin filaments form cross-bridges as a result of which the two myofilaments slide past each other. Unlike skeletal muscle, however, there appears to be no troponin, the calcium-binding protein on the actin myofilament that regulates actin-myosin cross-bridging. Calmodulin is the calcium-binding protein of smooth muscle. Smooth muscle cells have an abundant sarcoplasmic reticulum (SR). The rough or granular endoplasmic reticulum (ER) is the site of synthesis of new membranes, filaments and glycogen. The smooth ER (SR) is probably a site of storage of Ca2+ and release. Although control of contractile mechanisms is dependent upon intracellular Ca2+, it appears that only a minor contribution comes from this intracellular storage site. The transverse or T tubules, which form a continuation of the sarcolemma and pass into skeletal muscle fibres to connect with the SR, are absent in smooth muscle. The roles of myosin light-chain kinase, calmodulin and Ca2+ in the contractile responses of smooth muscle are described in Chapter 13.
Solanaceae glycoalkaloids: α-solanine and α-chaconine modify the cardioinhibitory activity of verapamil
Published in Pharmaceutical Biology, 2022
Szymon Chowański, Magdalena Winkiel, Monika Szymczak-Cendlak, Paweł Marciniak, Dominika Mańczak, Karolina Walkowiak-Nowicka, Marta Spochacz, Sabino A. Bufo, Laura Scrano, Zbigniew Adamski
Calcium ions play a crucial role in muscle contractions, and therefore, L-type calcium channels that move Ca2+ ions inward and trigger calcium release from the sarcoplasmic reticulum by activating the ryanodine receptor 2 (Striessnig et al. 2014) are just as important. Dysregulation of L-type Ca2+ channels is the basis of numerous cardiac disorders; therefore, they are also a common target in various therapies for cardiovascular diseases. L-type Ca2+ channel blockers, such as verapamil, are commonly used to treat hypertension, myocardial ischaemia, and arrhythmias (Limpitikul et al. 2018). The so-called α1 subunit forms the core of voltage-sensitive L-type Ca2+ channels. It associates with other subunits (β, α2δ, γ) to form heterooligomeric complexes. The β and α2/δ subunits are tightly but not covalently bound to the α1 subunit and modulate the biophysical properties and trafficking of the α1 subunit to the membrane (Bodi et al. 2005). The presence of L-type Ca2+ channels were also confirmed in the myocardium of Drosophila melanogaster (Limpitikul et al. 2018) and Musca domestica (Grabner et al. 1994). This tissue builds the dorsal vessel of the insect, traditionally called the heart. Even if not anatomically, the insect heart functionally and developmentally resembles the embryonic vertebrate heart. Thus, it offers an attractive alternative for studies conducted on mammals. Furthermore, many analyses can be performed in vivo without the need to sacrifice the test animal (Limpitikul et al. 2018).
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
Ultrastructural changes of EDL skeletal muscle tissues were evaluated by a transmission electron microscope. EDL muscle cells were found to have normal morphological properties in the control group and treatment (IR + TCA) group. It was determined that the myofibrils in sarcoplasm had a regular sequence and that the sarcomere structure was protected. Also it was observed that the mitochondrion located between the myofibrils, the sarcoplasmic reticulum (SR) cisternae and other organelles were in a regular structure (Figure 6A,B). EDL muscle cells were generally found to have normal morphological properties in the group with I-R injury (IR + SF) (Figure 7A). Moreover, enlargement of SR cisternae (Figure 7B) and thinning of myofibrils (Figure 7C) were observed in some cells in the IR + SF group.
Potential targets of gene therapy in the treatment of heart failure
Published in Expert Opinion on Therapeutic Targets, 2018
Jakub Rosik, Bartosz Szostak, Filip Machaj, Andrzej Pawlik
S100A1 is the main member of the S100 family in cardiac cells. Its distribution is uneven, and the highest protein concentrations of S100A1 are located in the left ventricles of adult hearts [26,27]. S100A1 plays a pivotal role in the regulation of numerous other proteins in cardiomyocytes; for example, it interacts with SERCA2a in a calcium-dependent manner to increase protein levels and activity. Ryanodine receptors, which play a huge role in calcium circulation, are also regulated by S100A1. The protein improves calcium release from the sarcoplasmic reticulum. S100A1 also modifies L-type calcium channels and the sodium-calcium exchanger. Apart from regulating calcium circulation, S100A1 is also present in mitochondria and interacts with various mitochondrial enzymes. Its interaction with F1-ATPase in a calcium-dependent and pH-dependent manner leads to an increase in enzyme activity. As a result, ATP generation is enhanced, and cells expressing S100A1 tend to have higher ATP concentrations [10,27–32]. It was shown that levels of S100A1 protein were reduced in cells in a HF model. Therefore, knowing the immense influence of S100A1 on cardiac cell contractility, energetic homeostasis and calcium circulation, it has become a promising target for gene therapy [26,27,29,31–33].