Muscles fast-twitch

Using the values in Table 24.1 for body glycogen content and the data in part b of the illustration for A Deeper Look (page 759), calculate the rate of energy consumption by muscles in heaty exercise (in J/sec). Use the data for fast-twitch muscle. 

Calcineurin Cytosol A calmodulin-regulated protein phosphatase. May play important roles in cardiac hypertrophy and in regulating amounts of slow and fast twitch muscles. 

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. 

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. 

Parvalbumin is another protein in search of a function. It contains three HLH motifs (Mr 1 IK), but only the second and third are functional Ca " -binding sites. These are high-affinity Ca /Mg sites, and both are filled with Ca in the known crystal structures (references in Table I). In fast twitch muscle, where most parvalbumins are found, the protein is postulated to act as a Ca " buffer (Haich a/., 1979 Gi s etal., 1982). As Ca is released from troponin C after muscle contraction, the Ca may be bound by parvalbumin to prevent reinitiation of contraction. In resting cells parvalbumin likely binds Mg ", rather than Ca (Haiech etal., 1979). 

It is not clear why clinical symptoms of DD are restricted to the epidermis and predominate to certain areas of the skin. A possible explanation could be that non-cutaneous tissues have compensatory mechanisms that are missing in the skin. SERCA1 expression is limited to fast-twitch muscles, but SERCA3 appears to be co-expressed with SERCA2b in a majority of tissues except the epidermis... 

Hong SJ, Chang CC (1998) Evaluation of intrinsic modulation of synaptic transmission by ATP in mouse fast twitch muscle. J Neurophysiol 80 2550-8 Hunt JM, Redman RS, Silinsky EM (1994) Reduction by intracellular calcium chelation of acetylcholine secretion without occluding the effects of adenosine at frog motor nerve endings. Br J Pharmacol 111 753-8... 

Notes Found only in adult fast twitch muscle. bFound only in neonatal muscle. 

In many instances, however, the functional differences between two isoforms appear too subtle to justify the existence of both forms. Hence, SERCAla and SERCA2a Ca2+-pumps are functionally indistinguishable in the assays available, and both are susceptible to inhibition by phospholamban. Since phospholamban is expressed mainly in the tissues, where SERCA2a is present (i.e., in cardiac and slow twitch muscle), and not where SERCAla is present (fast twitch muscle), the regulation by phospholamban appears much more isoform specific than it actually is. 

Dudley, G. A. and Terjung, R. L. (1985) Influence of acidosis on AMP deaminase activity in contracting fast-twitch muscle. 

Two percent to 3% of the thiamin in nervous tissue is present as the triphosphate, which also occurs in significant amounts in skeletal muscle, especially in fast-twitch muscle fibers. In the nervous system, the triphosphate is found exclusively in the membrane fraction muscle thiamin triphosphate is mainly cytosoUc. There are two pathways for formation of thiamin triphosphate from the diphosphate ... 

It is well established that AChE exists in nerves and muscles in a range of globular and asymmetric molecular forms. A wide variety of sedimentation profiles have been established for AChE moleeular forms in different mammalian muscles (Massoulie and Bon, 1982). The variations seen in the ratios of these moleeular forms between different muscles are wide and eomplex. Qualitative and quantitative variations exist among different species, as well as young versus adult (Barnard et al, 1984). In the rat extensor digitorum longus (EDL, a fast twitch muscle), the... 

Racay P, Gregory P, Schwaller B. Parvalbmnin deficiency in fast-twitch muscles leads to increased slow-twitch type mitochondria, but does not affect the expression of fiber specific proteins. FEBS J. 2006 273 96-108. 

In some tissues (insect flight muscle, fast twitch muscle) the reducing equivalents of NADH must be pumped against a gradient at a cost of 1 ATP (it is used to make FADH2). ... 

Crespo-Armas A, Azavache V, Torres SH, Anchustegui B, Cordero, Z. Changes produced by experimental hypothyriodism in fibre type composition and mitochondrial properties of rat slow and fast twitch muscles. Acta Cientrfica Venezolana 1994 45 42-44. 

Table XXVIII-1. Type I (Slow Twitch) versus Type II (Fast Twitch) Muscles...

When one examines muscle tissue that has been surgically removed, one finds two predominant types of muscle fibers. Fast twitch muscle fibers are large, relatively plump, pale cells. 

Eemandez, H.L. and Donoso, A., Exercise selectively increases G4 AChE activity in fast twitch muscle, J. Appl. Physiol, 65, 2245, 1988. 

The great bulk of our knowledge of the struc-ture/function relationships of TMs is based on studies with the skeletal fast-twitch muscle proteins, and so it is appropriate in what follows to describe the characteristics of the smooth muscle TMs in a comparative way with those of its skeletal muscle counterparts. 

FIGURE 4 Comparison of skeletal and smooth muscle TM primary structures. Shaded areas represent alternatively spliced exons, which are different in the smooth muscle a- and p-TM chains when compared with those in skeletal muscle. Nonshaded areas are identical in smooth muscle and skeletal fast-twitch muscle a-TM chains. This is true also of the smooth and skeletal muscle p-TM chains. Exon boundaries for the a gene are for the highly homologous quail genomic sequence (Lindquester et ah, 1989). These are at identical amino acid positions as for the product of the p gene (Libri et ah, 1989 Forry-Shardies et al., 1990). 

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