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  • 1
    Electronic Resource
    Electronic Resource
    Differential distribution of dystrophin and β-spectrin at the sarcolemma of fast twitch skeletal muscle fibers (1999)
    Springer
    Journal of muscle research and cell motility 20 (1999), S. 383-393 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We used double label immunofluorescence and confocal microscopy to examine the organization of β-spectrin and dystrophin at the sarcolemma of fast twitch myofibers in the Extensor Digitorum Longus (EDL) of the rat. Both β-spectrin and dystrophin are concentrated in costameres, a rectilinear sarcolemmal array composed of longitudinal strands and transverse elements overlying Z and M lines. In contrast, intercostameric regions, lying between these linear structures, contain significant levels of dystrophin but little detectable β-spectrin. The dystrophin-associated proteins, syntrophin and β-dystroglycan, are also concentrated at costameres but, like dystrophin, are present in intercostameric regions as well. Dystrophin is present at costameres and intercostameric regions in fast twitch muscles of the mouse but is absent from all regions of the sarcolemma in the mdx mouse, which lacks dystrophin. Areas of the sarcolemma near myonuclei also contain dystrophin without β-spectrin, consistent with the idea that the distribution of dystrophin at the sarcolemma is not dependent on β-spectrin. We conclude that dystrophin is present under all areas of the sarcolemma. The increased fragility of the sarcolemma in patients with Duchennes muscular dystrophy may be explained in part by the absence of dystrophin not only from costameres, but also from intercostameric regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005512217552
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  • 2
    Electronic Resource
    Electronic Resource
    Clustered acetylcholine receptors have two levels of organization in Xenopus muscle cells (1994)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 28 (1994), S. 179-193 
    Details
    ISSN: 0886-1544
    Keywords: acetylcholine receptor ; deep-etch replication ; sarcolemma ; cytoskeleton ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We studied the organization of acetylcholine receptor (AChR) clusters by shearing cultured Xenopus muscle cells with a stream of buffer, and preparing rotary replicas of the exposed cytoplasmic surface of the sarcolemma. AChR clusters contained numerous particles that protruded from the sarcolemma and formed an irregular array composed of discrete aggregates. AChR were located within these particle aggregates, as shown by comparison of the replicas to labeling by fluorescent α-bungarotoxin, and by immunogold cytochemistry with antibodies specific for the receptor. The aggregates were cross-linked by a dense network of 7 nm filaments that replicated with the banded pattern characteristic of actin microfilaments. The organization of receptors into the small aggregates was independent of the organization of these aggregates into clusters, as alkaline extraction removed the microfilament network and disrupted the irregular array of particle aggregates, but did not disperse individual receptors from the aggregates. We conclude that two levels of interactions organize AChR clusters in Xenopus muscle cells: short-range interactions that assemble individual AChR into small aggregates, and long-range interactions, perhaps mediated by actin microfilaments, that anchor the aggregates into larger clusters. © 1994 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970280209
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  • 3
    Electronic Resource
    Electronic Resource
    Clathrin-coated membrane: A distinct membrane domain in acetylcholine receptor clusters of rat myotubes (1990)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 15 (1990), S. 121-134 
    Details
    ISSN: 0886-1544
    Keywords: clathrin ; cell-substrate adhesion ; freeze fracture ; quick-freeze ; deep-etch ; rotary- replication ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have used antibodies to clathrin light chains in immunocytochemical studies of acetylcholine receptor (AChR) clusters of cultured rat myotubes. Immunofluorescence and ultrastructural experiments show that clathrin is present in coated pits and in large plaques of coated membrane. Coated membrane plaques are spatially and structurally distinct from AChR-rich membrane domains and the bundles of microfilaments that are also present in AChR clusters. Clusters contain a relatively constant amount of clathrin light chain protein, which is not dependent on the amount of AChR. Clathrin plaques remain after AChR domains are disrupted by azide, or after microfilament bundles are destabilized by cytochalasin D. Extraction of myotubes with saponin removes clathrin without disrupting AChR domains. Thus, clathrin plaques, microfilament bundles, and AChR-rich domains are independently stabilized.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970150208
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  • 4
    Electronic Resource
    Electronic Resource
    Ultrastructure of the human erythrocyte cytoskeleton and its attachment to the membrane (1991)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 19 (1991), S. 227-243 
    Details
    ISSN: 0886-1544
    Keywords: spectrin ; band 3 ; anion transporter ; membrane structure ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We attached paraformaldehyde-fixed human erythrocyte ghosts to coated coverslips and sheared them to expose the cytoskeleton. Quick-freeze, deep-etch, rotary-replication, or tannic acid/osmium fixation and plastic embedding revealed the cytoskeleton as a dense network of intersecting straight filaments. Previous negative stain studies on spread skeletons found 5-6 spectrin tetramers intersecting at each actin oligomer, with an estimated 250 such intersections/μm2 of membrane. In contrast, we found 3-4 filaments at each intersection and ∼400 intersections/μm2 of membrane. Immunogold labeling verified that the filaments were spectrin, but their lengths (29-37 nm) were approximately one-third that of extended spectrin dimers. The length and diameter of the filaments were sufficient to accommodate spectrin dimers, but not spectrin tetraments. Our results suggest that, in situ, spectrin dimers may associations as hexamers and octamers, rather than tetramers. We present several explanations that can reconcile our observations on intact cytoskeletons with previous reports on spread material.Extracting sheared ghosts with solutions of low ionic strength removed the cytoskeleton to reveal projections from the cytoplasmic surface of the membrane. These projections contained band 3, as shown by immunogold labeling, and they aggregated to a similar extent as intramembrane particles (IMP) when the cytoskeleton was removed, suggesting a direct relationship between these structures. Quantification indicated a stoichiometry of 2 IMP for each cytoplasmic projection. Cytoplasmic projections presumably contain other proteins besides band 3 since further treatment with high ionic strength solutions extracts peripheral proteins and reduces the diameter of projections by ∼3 nm.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970190402
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