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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 subunit nature of the myosin molecule can be examined using in-vitro enzymatic treatments (165). For example, trypsin proteolysis cleaves myosin molecules into two subunits, heavy meromyosin (HMM) and light meromyosin (LMM). Papain treatment of HMM yields a linear fragment (HMM-S2) and a globular fragment (HMM-S1) containing two myosin heads. The HMM-S1 fragment contains myosin heavy chains (MHC), which are largely responsible for ATPase activity; thus, the MHC “heads” are the primary force-generating sites. As a result of the ATPase activity in the MHC, they are also primarily responsible for the sarcomere and ultimately muscle fiber shortening velocity (23, 58, 151). In the neck region of the S1 fragment (Figure 1.9), each of the heads is bound to two molecules of 20 kD light myosin (LMC) proteins that modulate the ATPase activity of the globular heads. Modulation likely occurs as a result of LMC regulation of the velocity of the power stroke during contraction (123). Importantly, isoforms of MHC and MLC are the primary determinants of human skeletal muscle fiber type classification (11, 19, 20, 75, 113, 130, 174). There are two basic isoforms of the MHC – fast and slow – and at least four isoforms of LMC; different combinations of MHC and LMC create fibers with different contractile characteristics (see Table 1.1).
Understanding the Power
Published in Gowri Dorairajan, Management of Normal and High Risk Labour During Childbirth, 2022
Biomolecular basis of uterine contraction: The uterine myofibril has actin and myosin proteins. The former produces thin and the latter dense contractile filaments – the two crosslink to bring about the contraction. The myosin protein has to be activated by phosphorylation. This activation is brought out by light-chain kinase in the presence of the calmodulin calcium complex. Any stimulus that increases intracellular calcium level will increase the contraction. Calcium concentration increases when oxytocin receptors bind oxytocin. This is brought out by stimulating phospholipase C and cyclic adenosine monophosphate (cAMP), which help release calcium from the sarcoplasmic reticulum. Prostaglandins stimulate calcium release. Progesterone and alpha-adrenergic increase while beta-adrenergic reduces cAMP, and hence the intracellular calcium levels.
Functional Anatomy
Published in James Crossley, Functional Exercise and Rehabilitation, 2021
The myofibril structure of myosin and actin allows contraction of muscle. Actin and myosin run parallel with each other. The thick myosin filaments have small heads called cross bridges. Folllowing electrical stimulus from a motor neuron, cross bridges interact with, bind to and pull against the thin actin filaments. This pulls the actin and myosin filaments together to produce movement, a process referred to as the sliding filament theory.
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].
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 are crucial for the contraction of all types of muscles. After influx into the cytoplasm, they interact with myofilaments and ultimately allow for interaction between myosin and actin filaments, and thus for muscle contraction. Since they are a trigger and an executor of muscle contractions, their concentration in the sarcoplasm must be strictly regulated. In striated muscles, cell membrane depolarization is a signal that initiates the cascade responsible for muscle contraction. Changes in the cell membrane potential activate and open the L-type calcium channels. Then, the local increase in Ca2+ concentration activates the ryanodine receptor, a sarcoplasmic calcium channel, which releases the next portion of calcium ions into the cytoplasm, which interacts with myofilaments.
Myosin light chain kinase regulates intestinal permeability of mucosal homeostasis in Crohn’s disease
Published in Expert Review of Clinical Immunology, 2020
Many studies have demonstrated how MLCK directly regulates the ability of the cytoskeleton to activate the TJ barrier [48,53,54]. Ca2+/calmodulin-dependent MLCK phosphorylates the myosin RLC and activates myosin in the smooth muscle. Then, ATPase in the myosin head is activated to hydrolyze ATP, thereby converting the chemical energy to mechanical forces and motion [55]. At the same time, actin assembles to form actin filaments. Then, the heavy chain motor domain of myosin reversibly binds to actin filaments, leading to cyclic interaction between actin and myosin. With hydrolyzation of ATP (the basis of energy) and assembly of actin (the basis of structure), interaction between MLCK and skeletal proteins contributes to the interplay and contraction of skeletal proteins, finally leading to contraction of the intestinal cells [39]. With contraction of the cytoskeleton, the paracellular pathways sealed by the TJ are activated to increase intestinal permeability. Additionally, Rho-associated kinase (ROCK) has a similar role in myosin phosphorylation and activation [56].