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  • 1
    Electronic Resource
    Electronic Resource
    Normal variations in presynaptic active zones of frog neuromuscular junctions (1983)
    Springer
    Journal of neurocytology 12 (1983), S. 317-323 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Neuromuscular junctions of frog cutaneous pectoris muscles were examined by the complementary-replica freeze-fracture technique. The large number of active zones revealed in this way permitted quantitation of normal and disrupted zones in control muscles and in muscles deprived of external calcium for periods of up to eight hours. Although some 87% of the active zones examined had the usual appearance of two double rows of intramembrane particles flanking a low ridge, several varieties of disrupted active zones appeared in which the rows were interrupted, dispersed, rotated, or reduced to single rows. The frequency of disruptions was not increased by calcium deprivation. Disorganized active zones at tips of neuromuscular junctions may represent normal remodelling of the junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01148467
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Distinctions between gap junctions and sites of intermediate filament attachment in the leech C.N.S. (1983)
    Springer
    Journal of neurocytology 12 (1983), S. 805-815 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Freeze-fracture studies on the nerve cord of the leechHirudo medicinalis reveal that the plasma membranes of various cells, including glial and muscle cells, contain at least two distinct types of aggregated intramembrane particles, identified as hemidesmosomes and gap junctions. Hemidesmosomes consist of angular particles irregularly arranged in circular or elongate patches in external leaflets (E-faces), and are associated with a bundle of intermediate filaments extending into the cytoplasm. Hemidesmosomes of specific axons abut on extracellular space at openings in the surrounding glial sheath. Gap junctions are patches of rounder particles in cytoplasmic leaflets (P-faces) and are more uniformly spaced; they have a corresponding array of pits in the complementary E-face. Gap junctions connect processes of adjacent smooth muscle cells, and apparently interconnect glial processes. Thus, different types of cells in the leech C.N.S. have similar intramembrane specializations. Moreover, the hemidesmosomes and gap junctions might, on superficial examination, be confused.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01258152
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    Paper (German National Licenses)
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Quick-freeze, deep-etch replication of cells in monolayers (1990)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 14 (1990), S. 342-347 
    Details
    ISSN: 0741-0581
    Keywords: Quick-freeze deep-etch rotary replication ; Cell monolayers ; Tissue culture ; Specimen preparation ; Freeze-etch artifacts ; Temperature control ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: We have made several technical improvements for quick-freeze, deep-etch replication of monolayers of cells grown on, or attached to, glass coverslips. Cells studied include muscle cells of rat and Xenopus cultured on glass coverslips, and erythrocytes attached to coverslips coated with poly-L-lysine. We describe methods for identifying particular areas of cultures, e.g., clusters of acetylcholine receptors on muscle cells, by light microscopy and then relocating these areas after replication. For good preservation of structure by quick-freezing, it is necessary to ensure that the surface to be frozen is covered by a minimum depth of water (〈 10 μm). Insufficient or excess water left on the sample during freezing causes recognizable artifacts in its replica. We describe two ways to control the water table-one by improving visual control of water removal, the other by blowing excess water off the sample surface with a jet of nitrogen applied during its descent to the freezing block. Finally, we describe a new specimen holder that allows us to etch and replicate six samples at once with good thermal contact between the stage and samples.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1060140409
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