Slow twitch

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... 

Histopathological examination shows the typical corelike lesions in a high proportion of muscle fibers in older patients this may amount to 100%. Most typically the cores are large and centrally-placed, but multiple cores may occur in the same fiber cross section. Most older patients show a striking predominance of type 1 (slow twitch oxidative) fibers and virtually all fibers with cores are type 1. Sometimes younger family members have more normal proportions of type 1 and type 2 fibers but, again, the cores are confined to the type 1 fibers. It is well established that muscle fiber types can interconvert due to altered physiological demands, and it is likely that fibers with cores convert to a basically slow twitch-oxidative metabolism to compensate for the fact that up to 50% of their cross sectional area may be devoid of mitochondria. 

Hypothyroid myopathy occurs in about 30% of patients with hypothyroidism irrespective of its cause. Muscle pain, cramps, and stiffness may be seen, and are often exacerbated by cold weather. Pseudomyotonic features of delayed muscle contraction and relaxation are common. Myoedema (the mounding phenomenon) is due to the painless, electrically silent contracture produced on direct percussion. Muscle biopsy often shows a predominance of type 1 (slow-twitch) fibers, again analogous to that seen in experimental hypothyroidism (Figure 22). Muscle hypertrophy with weakness and slowness of movement occurs in the Debre-Semelaigne syndrome seen in severely hypothyroid children, and Hoffman s syndrome is a similar condition seen in adults with hypothyroidism, but is also accompanied by painful spasms. 

Figure22. (a) Euthyroid(normal)ratmuscleshowingmixtureoftype1 (slow-twitch) and type 2 (fast-twitch) fibers, (b) Hypothyroid rat muscle showing uniformly type 1 (slow-twitch) histochemical profile myofibrillar ATPase after alkaline preincubation.

Muscle Fast twitch Slow twitch Rapid movement Sustained movement Glycolysis Aerobic pathways, eg, p-oxidation and citric acid cycle Glucose Ketone bodies, triacylglycerol in VLDL and chylomicrons, free fatty acids Lactate Lipoprotein lipase. Respiratory chain well developed. 

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-... 

Typel Slow Twitch Type II Fast Twitch... 

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

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 deduced amino acid sequences of the fast-twitch and slow-twitch isoforms of the sarcoplasmic reticulum Ca -ATPases... 

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],... 

Distinguish among the three types of muscle fibers slow-twitch oxidative, fast-twitch oxidative, and fast-twitch glycolytic... 

Feature Slow-twitch oxidative Fast-twitch oxidative Fast-twitch glycolytic... 

Fast-twitch muscle fibers develop tension two to three times faster than slow-twitch muscle fibers because of more rapid splitting of ATP by myosin ATPase. This enables the myosin crossbridges to cycle more rapidly Another factor influencing the speed of contraction involves the rate of removal of calcium from the cytoplasm. Muscle fibers remove Ca++ ions by pumping them back into the sarcoplasmic reticulum. Fast-twitch muscle fibers remove Ca++ ions more rapidly than slow-twitch muscle fibers, resulting in quicker twitches that are useful in fast precise movements. The contractions generated in slow-twitch muscle fibers may last up to 10 times longer than those of fast-twitch muscle fibers therefore, these twitches are useful in sustained, more powerful movements. 

Finally, slow-twitch muscle fibers have a small diameter. This facilitates the diffusion of oxygen through the fiber to the mitochondria where it is utilized. Taken together, each of these characteristics enhances the ability of these fibers to utilize oxygen. Therefore, in slow-twitch oxidative muscle... 

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... 

Ca2+ is pumped into the SR stores by specific ATPases, the SERCA pumps. Three SERCA genes have been identified and several alternatively spliced gene products. In muscles SERCA1 is predominantly expressed in fast-twitch striated muscles and SERCA 2 isoforms are dominant in slow twitch, heart and smooth muscles, with SERCA2a in the former two, and SERCA2b predominant in smooth muscle and non-muscle cells. SERCA3 has a widespread distribution. 

Fast-twitch muscle fibers have a high capacity for anaerobic glycolysis but are quick to fatigue. They are involved primarily in short-term, high-intensity exercise. Slow-twitch muscle fibers in arm and leg muscles are well vascularized and primarily oxidative. They are used during prolonged, low-to-moderate intensity exercise and resist fatigue. Slow-twitch fibers and the number of their mitochondria increase dramatically in trained endurance athletes. 

Type I is also known as slow twitch fibre. Type llAis also known as fast twitch, and fibre type IIB is also known as fast twitch. Data are from world-class athletes and from fibres in the quadriceps muscle. 

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. 

Haimoto H, Kato K. 1987. SlOOaO (alpha alpha) protein, a calcium-binding protein, is localized in the slow-twitch muscle fiber. J Neurochem 48(3) 917-923. 

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). 

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