Muscle contraction and

Biological functions of Ca(Il) ion are numerous but maybe classified ia one of three categories the formation of soHd skeletal material such as bone, teeth, and shell the stabilizing of proteia conformational stmcture and the most varied, the abiUty of Ca(Il) to trigger certain physiological activities such as muscle contraction and the release of hormones (qv). 

Certain proteins endow cells with unique capabilities for movement. Cell division, muscle contraction, and cell motility represent some of the ways in which cells execute motion. The contractile and motile proteins underlying these motions share a common property they are filamentous or polymerize to form filaments. Examples include actin and myosin, the filamentous proteins forming the contractile systems of cells, and tubulin, the major component of microtubules (the filaments involved in the mitotic spindle of cell division as well as in flagella and cilia). Another class of proteins involved in movement includes dynein and kinesin, so-called motor proteins that drive the movement of vesicles, granules, and organelles along microtubules serving as established cytoskeletal tracks. ... 

Mammals, fungi, and higher plants produce a family of proteolytic enzymes known as aspartic proteases. These enzymes are active at acidic (or sometimes neutral) pH, and each possesses two aspartic acid residues at the active site. Aspartic proteases carry out a variety of functions (Table 16.3), including digestion pepsin and ehymosin), lysosomal protein degradation eathepsin D and E), and regulation of blood pressure renin is an aspartic protease involved in the production of an otensin, a hormone that stimulates smooth muscle contraction and reduces excretion of salts and fluid). The aspartic proteases display a variety of substrate specificities, but normally they are most active in the cleavage of peptide bonds between two hydrophobic amino acid residues. The preferred substrates of pepsin, for example, contain aromatic residues on both sides of the peptide bond to be cleaved. 

Dihydropyridine receptor (DHPR) is a member of voltage-dqiendent Ca2+ channels (CaVi, L-type), which specifically binds to dihydropyridine derivatives, a group of the Ca2+ channel blockers. Cav 1.1 works as the voltage sensor for skeletal muscle contraction, and Cay 1.2, as Ca2+-influx channel for cardiac muscle contraction. 

If MLCK activates contraction by increasing myosin phosphorylation, then an increase in the activity of myosin light chain phosphatase, MLCP, by decreasing the fraction of myosin which is phosphorylated, should lead to relaxation from the active (contractile) state. Cyclic adenosine monophosphate (AMP) is a strong inhibitor of smooth muscle contraction and it has been suggested that activation of MLCP could result from its phosphorylation via cAMP activated protein kinase (see Figure 5). 

Eisenberg, E. Hill, T.L. (1985). Muscle contraction and free energy transduction in biological systems. Science 227,999-1006. 

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. 

G, a M, cholinergics a,-Adrenergics a,-Adrenergics T Phospholipase C- 3l T Phospholipase c- 32 T Muscle contraction and T Blood pressure... 

The major biochemical events occurring during one cycle of muscle contraction and relaxation can be represented in the five steps shown in Figure 49-6 ... 

Thus, Ca " controls skeletal muscle contraction and relaxation by an allosteric mechanism mediated by TpC, Tpl, TpT, tropomyosin, and F-actin. 

Since Ca is transferred from one side of the membrane to the other side in association with the Ca -ATPase, thermal fluctuation of critical regions of the Ca -ATPase influenced in specific ways through the phosphorylation of the enzyme by ATP may play a role in Ca translocation. Similar ideas have been proposed some time ago by Huxley [419] in relationship to crossbridge movements during muscle contraction and by Welch and others on the role of protein fluctuations in enzyme action [420-430]. 

The ATP molecule is a universal energy carrier in the cell, and it is the principal one. It will sustain all reactions and processes requiring Gibbs energy active ion transport (ion pump operation), biosynthesis of proteins and other substances, muscle contraction, and so on. It is also employed for temporary energy storage in the cell. 

Physical restraints (may be associated with isometric muscle contractions and worsening of hyperthermia)... 

Vascular Effects of Complement Activation. During complement activation a number of complement fragments (anaphylatoxins), which are polypeptides with inflammatory properties, are released. The anaphylatoxins C3a and C5a induce smooth muscle contraction and enhance vascular permeability (H31). The most pronounced activation of complement with the formation of anaphylatoxins and terminal C5-9 complexes has been observed in septic shock (B29, B30, P2). Studies indicate that there is a relation between high concentrations of anaphylatoxins and C5-9 complexes and the development of ARDS or MODS in patients with sepsis (H10). 

Isotonic contraction occurs when the muscle shortens under a constant load. For example, when an object is lifted, the muscle contracts and becomes shorter although the weight of the object remains constant. In addition to moving external objects, isotonic contractions are performed for movements of the body, such as moving the legs when walking. 

Bronchial smooth muscle tone. Changes in bronchial smooth muscle tone are particularly important in the bronchioles compared to the bronchi. Recall that the walls of the bronchioles consist almost entirely of smooth muscle. Contraction and relaxation of this muscle has a marked effect on the internal radius of the airway. An increase in bronchial smooth muscle tone, or bron-choconstriction, narrows the lumen of the airway and increases resistance to... 

Another reductionist fallacy is the claim that a biochemical process can cause a physiological process. As pointed out by Rose (1998) a biochemical reaction such as the interaction between actin and myosin is not the cause of a physiological event such as muscle contraction. The biochemical process does not precede muscle contraction and therefore cannot cause it ... 

Prostaglandins F2a and E2 (E. J. Corey) members of a family of hormones that mediate blood pressure, smooth muscle contraction, and inflammation (Section 13.11D). 

The title compound, [8,9,10,11-13C4]LTC4, 83, an ideal internal standard for GC/MS and other MS determinations of cysteine containing leukotrienes which show biological effects at very low concentration, such as smooth muscle contraction and hypersensitivity reactions73, has been obtained74 in a reaction sequence shown in equations 32a and b. 

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