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Functional Properties of Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Ca2+ bind to the protein calmodulin (Section 6.3.1), which activates the enzyme myosin light chain kinase (MLCK). This enzyme phosphorylates the myosin light chain in the myosin head, in the presence of ATP. Only when the myosin head is phosphorylated can it combine with actin to form cross bridges and initiate cross-bridge recycling through ATP splitting. To relax the muscle, the myosin is dephosphorylated by the enzyme myosin light chain phosphatase, which is continuously active in smooth muscle. However, when the concentration of Ca2+ rises, the rate of phosphorylation exceeds that of dephosphorylation and cross-bridge recycling occurs. The converse applies when the concentration of Ca2+ falls.
Pulmonary Vascular Mechanobiology
Published in Jiro Nagatomi, Eno Essien Ebong, Mechanobiology Handbook, 2018
Diana M. Tabima Martinez, Naomi C. Chesler
The primary function of pulmonary vSMCs in mature animals is to control blood flow and pressure distribution via contraction and relaxation. SMC contraction is directly related to the concentration of calcium in the cytosol. An increase in the amount of Ca2+ results in activation of myosin light-chain kinase, which allows for cycling of cross bridges between actin and myosin resulting in SMC contraction.149
Plyometric exercise enhances twitch contractile properties but fails to improve voluntary rate of torque development in highly trained sprint athletes
Published in European Journal of Sport Science, 2022
Haiko Bruno Zimmermann, Filipe Estácio Costa, Raphael Sakugawa, Brian MacIntosh, Fernando Diefenthaeler, Juliano Dal Pupo
Postactivation potentiation (PAP) is a phenomenon traditionally characterized as an increased contractile response for a known activation observed after a voluntary conditioning contraction (i.e. conditioning activity [CA]) (MacIntosh, 2010; MacIntosh, Robillard, & Tomaras, 2012). The primary mechanism responsible for PAP relies on myosin light chain kinase (MLCK), which is activated by increased intracellular free [Ca2+], and results in phosphorylation of the regulatory light chains of myosin (Grange, Vandenboom, & Houston, 1993). This phosphorylation promotes mobility of the myosin heads and increases the probability of cross-bridge interaction (MacIntosh, 2010). To confirm the presence of PAP, contractile response (twitch) after supramaximal single-pulse electrical stimulation needs to be monitored before and after the CA. These stimuli allow assessment of any improvement in the muscle’s intrinsic contractile response and help to determine the time-course over which the muscle demonstrates PAP after the CA. PAP confirmation through electrical stimulation has been extensively used in previous studies and, in general, increased twitch peak torque (PT) and/or rate of torque development (RTD) ranging from 10.7% to 60% has been reported (Bergmann, Kramer, & Gruber, 2013; Folland, Wakamatsu, & Fimland, 2008; Fukutani, Miyamoto, Kanehisa, Yanai, & Kawakami, 2012, 2013, 2014; Hodgson, Docherty, & Zehr, 2008; Mitchell & Sale, 2011).
The effect of calcium co-ingestion on exogenous glucose oxidation during endurance exercise in healthy men: A pilot study
Published in European Journal of Sport Science, 2021
Ben J. Narang, Gareth A. Wallis, Javier T. Gonzalez
The typical intestinal glucose absorption pathway consists of an active component mediated by SGLT1 at the apical membrane of the enterocyte, followed by the passive transport of glucose across the basolateral membrane via GLUT2 (Röder et al., 2014). When luminal glucose concentrations are high, transport across the brush border membrane is thought to be facilitated by apical GLUT2 insertion (Chaudhry et al., 2012), resulting in a greater capacity for glucose uptake into the enterocyte. Thus, any factor that can influence apical GLUT2 expression has the potential to alter the absorption and subsequent metabolism of exogenous glucose. The putative role for calcium in apical GLUT2 insertion relates to both cytoskeletal rearrangement of the enterocyte (Turner, 2000) and SGLT1-dependent expression of PKC βII (Hug & Sarre, 1993). Morgan, Mace, Affleck, and Kellett (2007) demonstrated the necessity of calcium for myosin light chain kinase (MLCK) activity in isolated rate intestine, and in turn showed a facilitative role for MLCK activity in intestinal glucose absorption. Furthermore, these authors demonstrated a decrease in PKC βII expression in a calcium-deplete rat intestine (Mace et al., 2007; Morgan et al., 2007). However, despite the putative effect of calcium on intestinal glucose absorption, the present study shows that the addition of high-dose calcium to 1.2 g min−1 glucose does not enhance exogenous carbohydrate oxidation during endurance exercise.