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  • 1
    Electronic Resource
    Electronic Resource
    Substructure of membrane-bound Na+−K+-ATPase protein (1979)
    Springer
    Pflügers Archiv 381 (1979), S. 127-135 
    Details
    ISSN: 1432-2013
    Keywords: Na+−K+-ATPase ; Rat kidney ; Electron microscopy ; Substructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Purified membrane-bound Na+−K+-ATPase from rat kidney outer medulla was studied by freeze-fracturing, by freeze-etching and by negative staining. Freeze-fracturing of purified Na+−K+-ATPase membranes shows intramembraneous particles with a diameter of about 100 Å. The frequency of these intramembraneous particles — as estimated from the particle densities on the two fracture faces — lies between 4700 and 5600 particles per μm2. Applying rotary shadowing a four partite substructure could be detected in these intramembraneous particles observed on the fracture planes. The same four partite substructure was detected in particles observed on freeze-fractured and rotary shadowed intact baso-lateral plasma membranes of the thick ascending limb of Henle's loop. Particles could be also detected on both membrane surfaces of the purified Na+−K+-ATPase. These surface particles have about the same diameter and are present at about the same frequency as those observed within the freeze-fractured membranes. Negative staining of isolated Na+−K+-ATPase membranes showed particles on both membrane surfaces with a diameter between 30 and 50 Å, at a frequency of about 19,000 per μm2. On aspects of membrane edges we observed structures which suggest a transmembraneous connection of the negatively stained particles on both membrane surfaces. Our results suggest that the Na+−K+-ATPase protein is composed of four units and that each unit spans the cell membrane. The native enzyme structure of the Na+−K+-ATPase protein seems to be preserved during freeze-fracturing and freeze-etching. It is proposed that the four enzyme units of the Na+−K+-ATPase complex are dissociated during the negative staining procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582343
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Electron-microscopic demonstration of the distribution of calcium deposits in the exocrine pancreas of the rat after application of carbachol, atropine, cholecystokinin, and procaine (1984)
    Springer
    Cell & tissue research 235 (1984), S. 683-690 
    Details
    ISSN: 1432-0878
    Keywords: Exocrine pancreas ; Calcium pool ; Calcium release ; Electron microscopy ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In an attempt to identify a cellular Ca2+-pool, from which calcium is released when secretagogues are applied, tissue fragments of the rat exocrine pancreas were incubated and fixed with glutaraldehyde in the presence of calcium. By means of this procedure electron-dense deposits were found on plasma membranes. X-ray microanalysis showed that these deposits contain calcium. Stimulation of tissue fragments with the use of the secretagogues carbachol or cholecystokinin reduced the number of deposits by about 80%. When the antagonist atropine was applied after carbachol stimulation, deposits reappeared on cell membranes, which then disappeared again after a second stimulation with cholecystokinin. In the presence of procaine, carbachol was inhibited and only slightly reduced the Ca2+-deposits on the plasma membranes. These results suggest that a calcium pool, from which calcium is released to induce enzyme secretion on stimulation, is located in the cell membrane
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00226969
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    Paper (German National Licenses)
    Fulltext
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