Regulation of muscle activity

The identification of the sarcoplasmic reticulum membranes as the intracellular calcium transport system involved in the regulation of muscle activity took considerable time and occurred at first quite fortuitously. Kielley and Meyerhof40, not aware of the existence of the sarcoplasmic reticulum, characterized it biochemically as an... 

Ca component of bones and teeth regulation of muscle activity... 

Similarly, the regulation of PDK activity is modified in adult muscle PDC. For example, PDK activity is inhibited by pyruvate and propionate (metabolites elevated during anaerobic metabolism) and is less sensitive to stimulation by elevated NADH/NAD+ and acetyl CoA/CoA ratios (Fig. 14.2) (Thissen et al, 1986 Chen et al, 1998). The effects of NADH and acetyl CoA on PDK activity are mediated by the degree of E3-catalysed oxidation and E2-catalysed acetylation of the inner lipoyl domain of E2 (Roche and Cate, 1977 Rahmatullah and Roche, 1985, 1987 Ravindran et al, 1996 Yang et al, 1998), so that the regulation of this phenomenon is complex and involves multiple interacting components. 

Some of the main types of cellular regulation associated with rhythmic behavior are listed in Table III. Regulation of ion channels gives rise to the periodic variation of the membrane potential in nerve and cardiac cells [27, 28 for a recent review of neural rhythms see, for example, Ref. 29]. Regulation of enzyme activity is associated with metabolic oscillations, such as those that occur in glycolysis in yeast and muscle cells. Calcium oscillations originate... 

Figure 3.12 The regulation of phosphorylase activity by reversible phosphoiylation. A reversible phosphorylation process is also known as an interconversion cycle the latter term is preferred in this text, since the individual reactions must be irreversible, which can be confusing if the term reversible is used to describe the overall process. In resting muscle, almost all phosphorylase is in the b form.

The sympathetic nervous system plays an important role in the involuntary regulation of cardiac activity, vascular tonicity, functional activity of smooth muscle, and glands by releasing endogenic adrenergic substances, cateeholines, from peripheral nerve endings into the synapses of the central nervous system (CNS). 

Specialized cells such as neurons and muscle cells are electrically excitable and controlled by transmitter and modulator substances. Chemicals can affect the regulation of the activities of such cells. This can occur by (i) alterations in a neurotransmitter, (n) receptor function, (Hi) intracellular signal transduction, or (iv) signal-terminating processes. 

FIGURE 15-24 Regulation of muscle glycogen phosphorylase by covalent modification. In the more active form of the enzyme, phosphorylase a, Ser14 residues, one on each subunit, are phosphorylated. Phosphorylase a is converted to the less active form, phosphorylase b, by enzymatic loss of these phosphoryl groups, catalyzed by phosphorylase a phosphatase (PP1). Phosphorylase b can be reconverted (reactivated) to phosphorylase a by the action of phosphorylase b kinase. 

Seals, D. R., and Victor, R. G. (1991). Regulation of Muscle Sympathetic Nerve Activity During Exercise in Humans. Exerc Sport Sci Rev 19 313—49. 

The present volume covers Muscle and Molecular Motors . The first few chapters describe the ultrastructures of striated muscles and of various muscle filaments (myosin, actin, titin), they discuss the regulation of muscle contractile activity, and they explore the mechanism of force production and movement. The book then sets out to survey other kinds of motor systems microtubules and their interactions with both microtubule associated proteins (MAPs) and the motor proteins kinesin and dynein, the major sperm protein in nematodes, the rotary ATPases driven by or driving proton gradients, and the action of motor enzymes, polymerases, on nucleic acids. The aim throughout is to explore different molecular mechanisms of motor action in order to identify common themes. 

Calcium is known to be an important key regulator for contractile activities of both skeletal and smooth muscles. There are two general mechanisms of regulation of muscle contraction actin based and myosin based. 

Study of the molecular biology of calcium regulation of muscle contraction was initiated by the discovery of a new protein factor sensitizing actomyosin to calcium ions (Ebashi, 1963 Ebashi and Ebashi, 1964). This protein factor was called native tropomyosin, because of its similarity in amino acid composition to tropomyosin, which had been discovered earlier (Bailey, 1946, 1948). It was soon found that this factor is a complex of tropomyosin and a new globular protein, termed troponin (Ebashi and Kodama, 1965 Ebashi et al., 1968). Thus four proteins, i.e., myosin, actin, troponin, and tropomyosin, are involved in calcium-regulated physiological muscle contraction (Ebashi et al., 1968, 1969 Ebashi and Endo, 1968). The contractile interaction between myosin and actin is depressed by troponin and tropomyosin in the absence of calcium ions. When calcium ion acts on troponin, this depression is removed and the contractile interaction is then activated (Figs. 1 and 2). 

If osmosis and simple diffusion were the only mechanisms for transporting water and ions across cell membranes, these concentration differences would not occur. One positive ion would be just as good as any other. However, the situation is more complex than this. Large protein molecules embedded in cell membranes actively pump sodium ions to the outside of the cell and potassium ions into the cell. This is termed active transport because cellular energy must be expended to transport those ions. Proper cell function in the regulation of muscles and the nervous system depends on the sodium ion/potassium ion ratio inside and outside of the cell. 

Petkov, G. V., Nelson, M. T. (2005). Differential regulation of Ca2- -activated K+ (BK) channels by 3-adrenoceptors in guinea pig urinary bladder smooth muscle. American Journal of Physiology. Cell Physiology, 288(6), C1255-C1263. 

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