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  • 1
    ISSN: 1573-7322
    Keywords: Sarcomere structure ; cardiomyocyte ; pathophysiology ; proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We present a classification of the proteins of the cardiomyocyte based on structural and functional properties of the various components of this cell. The following protein families are categorized: 1) the contractile proteins, responsible for the contractile properties; 2) the sarcomeric skeleton, including titin, α-actinin, myomesin, M-protein, and C-protein, that keeps the contractile filaments in register and ensures sarcomeric stability; 3) the cytoskeletal proteins, i.e., desmin and the microtubules, that maintain the structural order within the cell and connect the cytoplasm and all cellular organelles with the sarcolemma; 4) membrane-associated proteins, such as vinculin, talin, dystrophin, and spectrin, that link the structural components of the intracellular milieu with those of the extracellular matrix via the integrins; and 5) proteins of the intercalated disc, including the cadherins, catenins, desmoplakin, connexin 43, and several others, that ensure stability of the longitudinal cardiomyocyte connections and facilitate impulse conduction. This classification not only is useful from a structural point of view but also is reflected in the functional behavior of these proteins in different pathophysiological situations, e.g., acute ischemia or chronic damage such as heart failure. Structural alterations, as shown here in human myocardium with chronic heart failure, demonstrate a graded sensitivity to pathophysiologic stimuli in that the contractile proteins are the most sensitive proteins and the cytoskeleton and the membrane-associated proteins show a compensatory increase and are more resistant against noxious stimuli. From these findings, it is concluded that these reactions to degenerative chronic processes reflect the survival priorities of the cells.
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  • 2
    ISSN: 1573-7322
    Keywords: heart failure ; human ; cytoskeleton ; contractile dysfunction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In addition to functional alterations, heart failure has a structural basis as well. This concerns all components of the cardiac myocytes as well as the extracellular space. Proteins of the cardiomyocyte can be subdivided in 5 different categories: 1) Contractile proteins including myosin, actin, tropomyosin and the troponins. 2) Sarcomeric skeleton: titin, myosin binding protein C, α-actinin, myomesin, and M-protein. 3) True ‘cytoskeletal’ proteins: tubulin, desmin and actin. 4) Membrane-associated proteins: dystrophin, spectrin, talin, vinculin, ankyrin and others. 5) Proteins of the intercalated disc: desmosomes consisting of desmoplakin, desmocollin, desmoglein and desmin; adherens junctions with N-cadherin, the catenins and vinculin, and gap junctions with connexin. Failing myocardium obtained from patients undergoing cardiac transplantation exhibits ultrastuctural degeneration and an altered nucleus/cytoplasm relationship. The contractile proteins and those of the sarcomeric skeleton, especially titin, are downregulated, the cytoskeletal proteins desmin and tubulin and membrane-associated proteins such as vinculin and dystrophin are upregulated and those of the intercalated disc are irregularly arranged. Elevation of cytoskeletal proteins correlates well with diastolic and contractile dysfunction in these patients. The enlarged interstitial space contains fibrosis, i.e. accumulations of fibroblasts and extracellular matrix components, in addition to macrophages and microvascular elements. Loss of the contractile machinery and related proteins such as titin and α-actinin may be the first and decisive event initiating an adaptive increase in cytoskeleton and membrane associated components. Fibrosis may be stimulated by subcellular degeneration. The hypothesis is put forward that all proteins of the different myocardial compartments contribute to the deterioration of cardiac function in heart failure.
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  • 3
    ISSN: 1432-0878
    Keywords: Key words Vinculin ; Talin ; Integrin ; Dystrophin ; Spectrin ; T-tubule ; Costamere ; Basal membrane ; Cardiac muscle cell ; Dilated cardiomyopathy ; Human ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The transverse tubule system of the cardiomyocyte remains undeformed despite the extreme forces it undergoes during the contraction-relaxation cycle, but the morphological basis for its stability remains unclear. Therefore, we have investigated the architecture and subcellular protein scaffold of the cardiac T-tubules and compared it with that of the costameres and of the free sarcolemma. Tissue samples from normal rat and monkey hearts, and left ventricular tissue from normal and cardiomyopathic human hearts obtained at transplantation surgery were investigated using immunocytochemistry and confocal microscopy and by electron microscopy. In addition, we used a re-differentiation model of isolated, cultured adult rat cardiomyocytes. The cell membrane of the cardiac T-tubules was found to contain the cell-matrix focal adhesion molecules (FAMs) vinculin, talin, the α5β1 integrin and the membrane-associated proteins (MAPs) dystrophin and spectrin. FAMs and MAPs were localized in the T-tubular membrane in a similar pattern: in longitudinally oriented myocytes as transverse punctate lines at the Z-level; in transversally cut myocytes a radial tubular network was found to extend throughout the interior of the cell. Immunolabeling for basement membrane components including collagen IV, fibronectin and laminin showed a colocalization with FAMs and MAPs parallel to the transverse T-tubules. The costameres of the sarcolemma showed a protein composition resembling that of the T-tubules but the intervening segments of free sarcolemma showed absence of FAMs and presence of MAPs. For the first time, we demonstrate the existence and protein composition of the T-tubular scaffold in the human heart. Furthermore, we show that cardiomyocytes from human failing hearts have less abundant but more dilated T-tubules than do experimental animals. These results indicate that the cardiac T-tubular system contains a subcellular scaffold closely resembling that of the costameres. It consists of FAMs, MAPs and basal lamina proteins that confer structural integrity to the cardiac T-tubular membrane during contraction/relaxation cycles.
    Type of Medium: Electronic Resource
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