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Functional Properties of Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Cardiac muscle cells, also called cardiocytes or cardiac myocytes, are relatively small muscle cells 20–35 µm across and 100–150 µm long. The cells are packed with contractile myofilaments whose alignment gives a striated appearance, as in skeletal muscle (Figure 10.18). Most cardiocytes have a single nucleus, although a few may have two or more nuclei. Many cardiocytes show variable Y-shaped branching that allows a higher degree of interconnection between cardiocytes in the longitudinal direction, as illustrated by the two myocytes at the top of Figure 10.18.
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.
Diabetes Mellitus and Ischemic Heart Disease
Published in E.I. Sokolov, Obesity and Diabetes Mellitus, 2020
The first phase of energy formation includes the release of ionized hydrogen from the carbohydrates, fatty acids, and amino acids being oxidized. The formation of energy mainly occurs in the Krebs cycle. The second phase or cumulation and transportation of energy is associated with its deposition in the form of the energy of ATP, the formation of creatine phosphate, and the transfer of the macroergic phosphate bond to ADP. The third phase of utilizing energy includes its transformation, shortening of actomyosin, and work of the myofibrills. The energy produced by glycolysis is a sufficiently important factor of the contracting ability of the myocardium and ensures the following functions of a myocardial cell: (i) functioning of the calcium pump, (ii) transportation of the macroergic phosphates to the contractile proteins at the expense of activation of the cytoplasmic creatinphosphokinase, (iii) preparation of amino acids for inclusion in a Krebs cycle, and (iv) maintaining of the physiological positive potential of the action of a cardiac myocyte.
Beneficial cardiovascular and remodeling effects of SGLT 2 inhibitors
Published in Expert Review of Cardiovascular Therapy, 2022
Steven G. Chrysant, George S. Chrysant
Increase in intracellular sodium in cardiomyocytes hampers the antioxidant mitochondrial defence mechanism against production of reactive oxygen species, and causes disruptive effects on cardiomyocyte function [80–82]. SGLT2 inhibitors reduce intracellular sodium in cardiomyocytes independently of glucose metabolism and underlies their cardioprotective effects demonstrated n in randomized clinical trials [83–86]. The mechanism for the increased intracellular sodium in cardiac myocytes has been attributed to an increased activity of sodium-hydrogen exchanger (NHE) isoforms (NHE-1, NHE-3). The NHE-1 activity is increased in the heart [87], where as the activity of NHE-3 is increased in the renal epithelial cells and is responsible for the reabsorption of filtered sodium [88].
Cardioprotective effects of corilagin on doxorubicin induced cardiotoxicity via P13K/Akt and NF-κB signaling pathways in a rat model
Published in Toxicology Mechanisms and Methods, 2022
Jing Huang, Ying Lei, Shengping Lei, Xinwen Gong
Cardiac biomarkers are largely circulating molecules or proteins which can be found in blood. The levels of MYO, H-FABP, GP-BBP, TGF-β, cTnI and BNP were elevated in DOX induced rats, whereas corilagin treatment reduced these cardiac markers. No particular changes were observed in corilagin alone treated rats and control. These biomarkers are used for the primary analysis of myocardial infarction. Myoglobin is mainly found in the cytoplasm of cardiac myocytes. Serum analysis of myoglobin is necessary for the quick determination of heart attack and thrombolytic treatment (Klocke et al. 1982). In the vein of myoglobin, measurement of H-FABP is the primary detection for cardiac dysfunction which gets rapidly released into the blood during myocardial injury (De Groot et al. 2001). Glycogen phosphorylase isoenzyme BB (GP-BB) is the glucose provider for heart muscle cells and it is released upon cardiac injury (Lippi et al. 2013).
Omecamtiv Mecarbil use in systolic heart failure- Results of the GALACTIC-HF trial
Published in Expert Review of Clinical Pharmacology, 2021
Syed Raza Shah, Arroj Ali, Sohail Ikram
Cardiac myocytes contract through a cross bridging cycle between myosin and actin filaments, which is powered by ATP hydrolysis. Myosin binds to ATP, resulting in a weak binding of the complex with actin. Once the ATP is hydrolyzed to ADP, the myosin, actin, and ADP complex becomes tightly bounded. OM is an elective cardiac myosin activator, with no effect on smooth muscle or skeletal muscle myosin. It specifically binds to an allosteric site on the myosin protein leading to conformation changes which hasten the speed of ATP hydrolysis. Consequently, the allosteric binding of OM accelerates the weak binding of actin and myosin to stronger binding, resulting in more myosin bound to actin for a longer period of time. The accumulation of primed myosin heads for a more force generating interaction between myosin and actin during the cardiac cycle results in improved cardiac contraction. Furthermore, there is a noted improvement of systolic function with OM due to prolonged systolic ejection time and stroke volume without an increase in myocyte calcium concentration, velocity of contraction, or heart rate [4,5]. Overall, OM, has a less negative implication on cardiac myocytes when compared to other inotropic agents making OM an advantageous drug of choice for the treatment of HF.