Skeletal muscle slow twitch fibers

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

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. 

Anabolic steroids decrease catabolism and increase skeletal muscle protein synthesis. Whether this results in muscular hypertrophy or hyperplasia, or a combination of these, is unclear and probably depends upon the muscle studied. Different muscle types contain different cytosolic receptor numbers and, therefore, the response to anabolic steroids varies. Anabolic steroids initiate an increase in RNA polymerase activity and the synthesis of either structural or contractile proteins. In some muscles, anabolic steroids may increase the ratio of fast twitch to slow twitch fibers (Nimmo et al 1982, Snow et al 1982). Increased activity of enzymes involved in energy metabolism may also occur. However, the total glycogen content may remain unchanged (Hyyppa et al 1997). The effects are most profound in females and castrated males (Snow 1993). 

Skeletal muscle cells can be subdivided into type I and type IIfibers. Type I fibers are slow-twitch fibers that use primarily oxidative metabolism for energy, whereas the type 11 fibers (fast-twitch) use glycolysis as their primary energy-generating pathway. 

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-... 

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 ). 

Skeletal muscle (type I, slow twitch, or red fibers) 50,000 <1 3 97... 

Exercise limitation and functional disability in COPD have a complex, multifactorial basis. Ventilatory limitation is caused by increased airways resistance, static and dynamic hyperinflation, increased elastic load to breathing, gas exchange disturbances, and mechanical disadvantage and/or weakness of the respiratory muscles (4-6). Car-diocirculatory disturbances (7,8), nutritional factors (9), and psychological factors, such as anxiety and fear, also contribute commonly to exercise intolerance. Skeletal muscle dysfunction is characterized by reductions in muscle mass (10,11), atrophy of type I (slow twitch, oxidative, endurance) (12,13) and type Ila (fast twitch) muscle fibers (14), altered myosin heavy chain expression (15), as well as reductions in fiber capillarization (16) and oxidative enzyme capacity (17,18). Such a dysfunction is another key factor that contributes... 

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