Contractile systems muscle

It is reasonable to inquire at this point whether the principles that have been set forth above have any applicability to natural functioning contractile systems. Muscles are very intricately constructed fibrous structures developed by nature to convert chemical energy into mechanical work. Detailed and sophisticated electron microscopic and x-ray diffraction studies have established the fine structure of muscle. The chemical processes and enzymatic activity that are intimately involved... 

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. ... 

Of the several kinase activities which are important in smooth muscle, myosin light chain kinase, MLCK, is the one responsible for activation of the actin-myosin system to in vivo levels. MLCK is present in the other nonmuscle cell types which have the actin-myosin contractile system and all of these are probably activated in a manner similar to smooth muscle rather than by way of the Ca -troponin mechanism of striated muscle. MLCK from smooth muscle is about 130 kDa and is rather variable in shape. It is present in smooth muscle in 1-4 pM concentrations and binds with an equally high affinity to both myosin and actin. Thus, most MLCK molecules are bound to actin. Myosin light chain serine-19 is the primary target of smooth muscle myosin light chain kinase. 

While all muscles contain actin, myosin, and tropomyosin, only vertebrate striated muscles contain the troponin system. Thus, the mechanisms that regulate contraction must differ in various contractile systems. 

Mectianism of Action A cardiac inotropic agent that inhibits phosphodiesterase, which increases cyclic adenosine monophosphate and potentiates the delivery of calcium to myocardial contractile systems. Therapeutic Effect Relaxes vascular muscle, causing vasodilation. Increases cardiac output decreases pulmonary capillary wedge pressure and vascular resistance. 

In the contractile system of skeletal muscle cells, myosin and actin are specialized to transduce the chemical energy of ATP into motion (see Fig. 5-33). ATP binds tightly but noncovalently to one conformation of myosin, holding the protein in that conformation. When myosin catalyzes the hydrolysis of its bound ATP, the ADP and Pi dissociate from the protein, allowing it to... 

Actomyosin is generally extracted from fresh rabbit muscles by the use of buffered KCl solutions of an ionic strength of 0.5-0.6 y. (Weber-Edsall solution). The solubility curve of the isolated actomyosin at pH 7 shows an inflection at 0.25 y, above a value of 0.3 u the protein is completely soluble (Hasselbach et al., 1953). At low ionic strengths, actomyosin upon addition of ATP and provided Mg++ ions are present shows superprecipitation. By glycerol extraction, muscle fibers may be prepared to contain essentially only the contractile system. Such fibers will contract normally under the conditions mentioned above for the isolated actomyosin (Weber and Portzehl, 1952). The muscle fibril contains the actomyosin in the insoluble state and in an optimal spatial arrangement (cf. Section IV, A,2). 

The preliminary suggestion that dipeptide effect is directed toward synaptic junction was not irrefragable one, because they also stimulate working capacity at direct electrical stimulation of muscle [75]. The contractile system was not also involved in Severin s phenomenon whereas protection effect on muscle membranes and activity of membrane bound enzymes was extremely pronounced [5,6]. Carnosine effect can be partially mimicked by several pH-buffers confirming importance of proton buffering capacity of the molecule [27]. 

Proteins like actin and myosin function as essential elements in contractile system of skeletal muscle. 

This chapter discusses muscle, an actin filament system, and cilia, a microtubule system. These do not typify all contractile systems. In some actin filament systems, movement occurs in the absence of myosin, being driven... 

Regulation by myosin phosphorylation, which is of particular importance for smooth muscle, is a feature of the less specialized actomyosin contractile systems. In striated muscle it would appear that light chain phosphorylation has been relegated to a modulatory role in the cross-bridge cycle, and response to stimulation has been accelerated by the evolution of the troponin system located in the I filament. The consequence is that the rapid binding of calcium to one molecule of troponin C renders seven actin molecules available to interact with as many heads of myosin molecules as they can accommodate. In smooth muscle, binding of cal-... 

Muscles and Other Actin-Myosin Contractile Systems Actin and Myosin... 

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