Slow-twitch skeletal muscle

Fig. 1. Amino acid sequence homology between the neonatal fast-twitch and slow-twitch skeletal muscle forms of the Ca -ATPase. The sequence of the slow Ca -ATPase is shown above the neonatal fast-twitch form, with nonhomologous amino acids indicated by asterisks. The sequence of the slow ATPase is shifted to the right by one residue at residue 505 to allow realignment after the difference in sequence length. Ml-MlO, membrane spanning regions S1-S5, stalk sectors Tl, T2, major tryptic cleavage sites P,...

The cDNA clone for the neonatal rabbit fast-twitch skeletal muscle Ca -ATPase encodes for 1001 amino acids giving a product with an estimated molecular weight of 110 331 Da [8], The clone for the Ca -ATPase of slow-twitch skeletal muscle sarcoplasmic reticulum (S-Ca -ATPase) encoded for 997 amino acids with a relative molecular mass (Mr) of 109 529 kDa [42],... 

ATP2A2 12q23-q24.1 SERCA2a SERCA2b SERCA2c Heart, slow twitch skeletal muscle, brain All tissues (e.g.epidermis) Epithelial, mesenchymal and hematopoietic cell lines, monocytes Darier disease (dominant)... 

SERCA2a is expressed predominantly in the heart, in slow twitch skeletal muscle and in the brain, where it represents the main SERCA isoform. In contrast, SERCA2b is a house-keeping isoform, ubiquitously expressed in smooth muscle and non-muscle tissue (Wuytack et al., 2002). Although both isoforms are detectable in keratinocytes and dermal fibroblasts in culture, SERCA2b is the major isoform expressed in the epidermis from adult skin sections. SERCA2c is expressed in epithelial, mesenchymal and hematopoietic cell lines, and in monocytes (Table 1). 

Danieli-Betto, D., Esposito, A., Germi-nario, E., Sandona, D., Martinello, T., Jakubiec-Puka, A., et al. (2005) Deficiency of alpha-sarcoglycan differently affects fast-and slow-twitch skeletal muscles. Am J Physiol Regul Integr Comp Physiol 289, R1328-1337. 

The contractile proteins of the myofibril include three troponin regulatory proteins. The troponin complex includes three protein subunits, troponin C (the calcium-binding component), troponin I (the inhibitory component), and troponin T (the tropomyosin-binding component). The subunits exist in a number of isoforms. The distribution of these isoforms varies between cardiac muscle and slow- and fast-twitch skeletal muscle. Only two major isoforms of troponin C are found in human heart and skeletal muscle. These are characteristic of slow- and fast-twitch skeletal muscle. The heart isoform is identical with the slow-twitch skeletal muscle isoform. Isoforms of cardiac-specific troponin T (cTnT) and cTnl also have been identified and are the products of unique genes. All cardiac troponins are localized primarily in the myofibrils (94%-97%), with a smaller cytoplasm fraction (3%-6%). 

Although it is less likely, cross-species differences in tissue distribution of isoenzymes could also potentially limit use of CK and LD injury (O Brien et al. 1997a). The distribution of tissue LDH isozymes differs with the various species of laboratory animals. For example, release of liver LDl and LD2 may occur with hepatopathy in some species (e.g., demonstrated in pigs, horses, bovines) and could confound interpretation of increases in blood LD. Similarly, interpretation of increased blood CK may be confounded by release of CK-MB by injury to other tissues such as slow-twitch skeletal muscle, nervous tissue, and uterine smooth muscle (e.g., parturition). Hemolysis could also potentially cause mild increases in these enzymes in certain species. 

FABP3 could be used as a biomarker if cardiotoxicity and renal disease are excluded (Pritt et al. 2008). It is found in highest concentration in heart and slow-twitch skeletal muscle. As a skeletal muscle biomarker, it has been shown to outperform CK-MM and AST with PPAR-alpha myotoxicity. 

SERCA2a is the principal form of the Ca -ATPase in adult slow-twitch skeletal and cardiac muscles and in neonatal skeletal muscles [8,9,42,53,54,67]. It is also... 

SERCA2a Slow-twitch skeletal, cardiac and smooth muscle Rabbit 997 109 529 MENA EPAILE 8, 42, 53, 54, 67... 

The smooth endoplasmic reticulum calcium pumps (SERCA) found in brain were first identified in sarcoplasmic reticulum. The three isoforms of SERCA are products of separate genes SERCA-1 is expressed in fast-twitch skeletal muscle SERCA-2a in cardiac/slow-twitch muscle SERCA-2b, an alternatively spliced form, is expressed in smooth muscle and non-muscle tissues SERCA-3 is... 

Divet, A., and Huchet-Cadiou, C., 2002, Sarcoplasmic reticulum function in slow- and fast-twitch skeletal muscles from mdx mice, Pflugers Arch, 444, pp 634-643. 

Lewis SEM, Kelly FJ, Goldspink DF (1984) Pre- and post-natal growth and protein turnover in smooth muscle, heart and slow- and fast-twitch skeletal muscle of the rat. Biochem J 217 517-526... 

It is possible, of course, to use direct calorimetry, often in combination with the indirect approach (OUR) to investigate the properties of muscle under different physiological conditions and in the diseased state. Chinet s group [70] found that the slow- and fast-twitch skeletal muscle fibres from the murine model of Duchenne muscular dystrophy had a reduced sarcoplasmic energy metabolism as measured by the combined direct and indirect calorimeter [69]. The possibility that this could be due to diminished glucose availability was then examined [71] but was dismissed in favour of decreased oxidative utilisation of glucose and free fatty acids, conceivably due to defective mitochondria. 

Tissue-Specific Expression. In adult rodents, PPAR.a is expressed in liver, kidney, intestine, heart, skeletal muscle, retina, adrenal gland, and pancreas. In adult human, PPARa is expressed in the liver, heart, kidney, large intestine, skeletal muscle (mostly slow-twitch oxidative type I fibers), and in cells of atherosclerotic lesions (endothelial cells, smooth muscle cells, and monocytes/macrophages). Therefore, regardless of... 

Skeletal muscle contains three types of fiber fast-twitch oxidative glycolytic (type 2A), fast-twitch glycolytic (type 2B), and slow-rwitch oxidative fibers (type 1). The proportion of each fiber type varies in different muscles. Different fiber types contain different isoforms of myosin, although there is no evidence that their mitochondria differ qualitatively. It has been reported that there are differences between subsarcolemmal mitochondria and those deeper in the same fiber but this has been questioned (see Sherratt et al., 1988 for references). 

SKELETAL MUSCLE CONTAINS SLOW (RED) FAST (WHITE) TWITCH FIBERS... 

Different types of fibers have been detected in skeletal muscle. One classification subdivides them into type I (slow twitch), type IIA (fast twitch-oxidative), and type IIB (fast twitch-glycolytic). For the sake of simphcity, we shall consider only two types type I (slow twitch, ox-... 

Skeletal muscle contains different types of fibers primarily suited to anaerobic (fast twitch fibers) or aerobic (slow twitch fibers) conditions. 

In 17 rats, twitch contraction of the anterior tibialis muscle in response to single Indirect stimuli continued until a mean dose of soman had been given that was more than 2.100 times the minimal dose that altered the magnitude of the twitch. 2 Eventual failure of the twitch response was seen to be always connected with marked slowing of the heart. This observation raises the possibility that the effect of soman on the twitch response of skeletal muscle depends on... 

Muscle contraction responses to different patterns of nerve stimulation used in monitoring skeletal muscle relaxation. The alterations produced by a nondepolarizing blocker and depolarizing and desensitizing blockade by succinylcholine are shown. In the train of four (TOF) pattern, four stimuli are applied at 2 Hz. The TOF ratio (TOF-R) is calculated from the strength of the fourth contraction divided by that of the first. In the double burst pattern, three stimuli are applied at 50 Hz, followed by a 700 ms rest period and then repeated. In the posttetanic potentiation pattern, several seconds of 50 Hz stimulation are applied, followed by several seconds of rest and then by single stimuli at a slow rate (eg, 0.5 Hz). The number of detectable posttetanic twitches is the posttetanic count (PTC)., first posttetanic contraction. 

There is probably no biological phenomenon that has excited more interest among biochemists than the movement caused by the contractile fibers of muscles. Unlike the motion of bacterial flagella, the movement of muscle is directly dependent on the hydrolysis of ATP as its source of energy. Several types of muscle exist within our bodies. Striated (striped) skeletal muscles act under voluntary control. Closely related are the involuntary striated heart muscles, while smooth involuntary muscles constitute a third type. Further distinctions are made between fast-twitch and slow-twitch fibers. Fast-twitch fibers have short isometric contraction times, high maximal velocities for shortening, and high rates of ATP hydrolysis. 

Mammalian skeletal muscle can be separated Into two distinct fiber populations, based on relative contraction characteristics, and are referred to as slow-twltch (Type I) or fast-twitch (Type II) fibers. The slow-twltch fiber type exhibits a relatively low shortening velocity (27), a low rate of tension development (27). a low myosin ATPase activity (28) and a low rate of calcium sequestration by the sarcoplasmic reticulum (29). The converse Is true for the fast-twitch fibers. Since contraction velocity highly correlates with myosin ATPase activity (30), It Is possible to easily Identify,... 

Similarly, measurements of blood flows to sections of muscle, which are primarily composed of a single fiber type, exhibit large differences consistent with the expected demands of oxygen supply based on mitochondrial content (32,33). Thus, mammalian skeletal muscle is typically comprised of three biochemically and functionally distinct fiber types slow-twitch red, fast-twitch red and fast-twitch white. These fiber types are also commonly referred to as Type I, Type Ila, and Type 11b, respectively (7 ). 

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