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  • 1
    Electronic Resource
    Electronic Resource
    Depolarization-induced calcium release from isolated triads measured with impermeant Fura-2 (1992)
    Springer
    The journal of membrane biology 128 (1992), S. 165-179 
    Details
    ISSN: 1432-1424
    Keywords: triads ; skeletal muscle ; excitation-contraction coupling ; sarcoplasmic reticulum ; fura
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Depolarization-induced Ca2+ release was studied in a mixture of triads and terminal cisternae isolated from rabbit skeletal muscle. The vesicles were actively loaded with known amounts of Ca2+ in the absence of precipitating anions in a solution containing 100 mm K propionate buffer. Changes in extravesicular Ca2+ were monitored with 10 μ m Fura-2 (membrane impermeant form). Ca2+ release was initiated by diluting an aliquot of the loaded vesicles into a TEACl release solution designed to maintain a constant [K+] · [Cl−] product. Fast release, defined as the percentage of total Ca2+ loaded which released in less than 10 sec, occurred when extravesicular free Ca2+ was in the submicromolar range and was unaffected by 5 mm caffeine under depolarizing conditions, change in external pH to 6.5, and an increase in external Mg2+ concentration from 0.1 to 0.2 mm. Thus, the Ca2+ release measured in these studies is distinct from Ca2+-induced Ca2+ release. The fast release more than doubled when a greater dilution (1 ∶ 20 versus 1 ∶ 10) of the loaded vesicles into the release solution, which would produce a larger depolarization, was used. The percentage of loaded Ca2+ which released rapidly in a particular triad preparation was similar to the percentage of vesicles structurally coupled as visualized by electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231810
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  • 2
    Electronic Resource
    Electronic Resource
    Membrane structural specialization of the toad urinary bladder revealed by the freeze-fracture technique (1978)
    Springer
    The journal of membrane biology 40 (1978), S. 281-296 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Examination of the toad urinary bladder by freeze-fracture electron microscopy reveals intramembrane particle arrays at a number of membrane sites. An array in which particles are aggregated into closely apposed parallel rows is found in the granular cell luminal membrane of dehydrated toads fixedin situ. These aggregates are structurally indistinguishable from those previously associated with vasopressin exposurein vitro. Aggregates are not found in granular cell luminal membrane in the case of hydrated toads fixedin situ. However, structurally similar arrays are found at low frequency in the membrane of cytoplasmic vacuoles in granular cells and in the plasma membrane of basal cells in both hydrated and dehydrated toads. Aggregates are also present at these sites in control and vasopressin-treated bladders fromin vitro expreiments. Particle arrays characteristic of gap junctions, desmosomes and hemidesmosomes also occur in the plasma membrane of basal cells. In addition, distinctive square arrays of particles exist in the plasma membrane of the bladder's mesothelium. Although a variety of intramembrane particle arrays exist in the toad urinary bladder, only the occurrence of organized particle aggregates in the luminal membrane of granular cells appears to be associated with vasopressin exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02026011
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  • 3
    Electronic Resource
    Electronic Resource
    Membrane structural and functional responses to vasopressin in toad bladder (1976)
    Springer
    The journal of membrane biology 30 (1976), S. 381-401 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Freeze-fracture electronmicroscopy demonstrates that vasopressin stimulation of isolated toad bladder results in a striking morphologic alteration of epithelial membrane structure. This alteration is characterized by the aggregation of intramembranous particles in orderly linear arrays at multiple sites in the luminal membranes of granular cells specifically. The size of these aggregates varies considerably, in terms of area, over a range from 0.5 to 70×10−3 μm2. The median aggregate size is about 10.5×10−3 μm2. Since the extent of vasopressin-associated particle aggregation, in terms of frequency of sites per area of membrane or cumulative area of membrane occupied by them, closely correlates with induced changes in transport function, as measured by osmotic water flow, the aggregates themselves appear to be of physiologic significance in the mechanism of action of vasopressin. This hypothesis is supported by the observations that sites of aggregation occur (a) in response to serosal exposure to hormone specifically, (b) independently of an osmotic gradient, and (c) following stimulation with cyclic adenosine monophosphate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869678
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  • 4
    Electronic Resource
    Electronic Resource
    Membrane structural specialization of the toad urinary bladder revealed by the freeze-fracture technique (1976)
    Springer
    The journal of membrane biology 29 (1976), S. 111-126 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Examination of the toad urinary bladder by freeze-fracture electron microscopy reveals that the mitochondria-rich cells of the epithelium possess distinctive and characteristic membrane structural specialization. Unique rod-shaped intramembrane particles are found in luminal and basal membranes as well as certain intracellular vesicles of this cell type. The consistent finding of two discrete patterns of luminal membrane structural organization supports the possibility that two morphological forms of mitochondria-rich cell exist within the toad bladder epithelium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868955
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  • 5
    Electronic Resource
    Electronic Resource
    Ultrastructural characterization of cholesterol distribution in toad bladder using filipin (1983)
    Springer
    The journal of membrane biology 74 (1983), S. 131-138 
    Details
    ISSN: 1432-1424
    Keywords: filipin ; 3β-hydroxysterols ; cholesterol ; toad bladder ; antidiuretic hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The polyene antibiotic filipin was used to characterize the cholesterol distribution in the membranes of the toad bladder epithelium in freeze-fracture replicas. The apical membranes of granular and mitochondria-rich cells incorporate moderate amounts of filipin while the basolateral membranes of both cell types incorporate substantially greater amounts. Intracellular membranes, in general, take up very little filipin. The major exception to this is the granule membrane, which appears to be rich in cholesterol. An inverse correlation was found between the density of filipin-sterol complexes in the apical membrane and the incidence of granules in the cytoplasm. This suggests that fusion of granules with the apical membrane may be responsible for variation in the concentration of cholesterol in the apical membrane. Thirty minutes following vasopressin exposure, there is no consistent change in the cholesterol content of the apical membrane of granular cells as measured by the incidence of filipin-sterol complexes. The lack of change in the amount of membrane cholesterol indicates that the vasopressin-induced increase in transepithelial water permeability is not mediated by a change in cholesterol content of the apical membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870502
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  • 6
    Electronic Resource
    Electronic Resource
    Membrane structural specialization of the toad urinary bladder revealed by the freeze-fracture technique (1975)
    Springer
    The journal of membrane biology 22 (1975), S. 385-402 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Examination of the toad urinary bladder by freeze-fracture electron-microscopy demonstrates structural specialization of the granular cell's luminal membrane compared to its basal membrane. Although both membranes appear to possess about 1,700 intramembranous particles per μm2, those of the luminal membrane tend to be significantly larger in size. In addition, the fracturing properties of the two membranes are markedly different: the majority of particles are found on fracture face B (outer membrane face), in the case of the luminal membrane, and the majority are found on fracture face A (inner membrane face), in the case of the basal membrane. While the two fracture faces of the basal membrane possess a similar distribution of particle sizes, in the case of the luminal membrane the B face was found to possess particles generally larger than those found on the A face. It was established that the probability of luminal membrane particles adhering to face B instead of face A is closely correlated with the size of the particle. The structural specialization of the granular cell's luminal membrane may have an important relationship to the characteristic permeability properties of this membrane and the capacity of this cell type to respond physiologically to the hormone vasopressin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868182
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  • 7
    Electronic Resource
    Electronic Resource
    ADH ACTION: EVIDENCE FOR A MEMBRANE SHUTTLE MECHANISM (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 372 (1981), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1981.tb15464.x
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  • 8
    Electronic Resource
    Electronic Resource
    Ultrastructure and immunocytochemistry of the isolated human erythrocyte membrane skeleton (1993)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 25 (1993), S. 30-42 
    Details
    ISSN: 0886-1544
    Keywords: spectrin ; cytoskeleton ; erythrocyte ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Isolated skeletons from human erythrocyte ghosts were studied using immunogold labeling; negative staining; and quick-freeze, deep-etch, rotary replication with Pt/C (QFDERR). Isolated skeletons visualized by QFDERR were similar to the negatively stained skeletons in that the proteins spectrin, actin, and ankyrin could be easily distinguished. However, the quick-frozen skeletons had two fewer filaments (4.2 ± 0.7) at an actin junction. Immunogold labeling of skeletons with site-specific spectrin antibodies not only confirmed the designation of these filaments as spectrin molecules, but indicated that about 30% of spectrin filaments form non-actin junctions consistent with the hexameric organization of these filaments. Many of the filaments displayed a striking banding pattern indicative of underlying substructure. Isolated skeletons prepared by QFDERR also showed evidence of laterally associated spectrin filaments. These associations, as well as many hexamer junctions, are lost during negative staining. Negative staining also apparently caused ∼21% of the spectrin filaments to separate into their monomeric subunits. These results indicate that the surface tension imposed during negative staining of isolated skeletons can cause a loss of interactions normally present in the intact membrane skeleton. © 1993 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970250105
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Composite replicas: Methodologies for direct evaluation of the relationship between intramembrane and extramembrane structures (1989)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 13 (1989), S. 216-227 
    Details
    ISSN: 0741-0581
    Keywords: Toad bladder ; Label fracture ; Colloidal gold ; Replica ; Membrane ; Freezing ; Glycocalyx ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Electron microscopic studies of membrane structure have been facilitated by the recent development of the composite replica technique in which the membrane is freeze-fractured, then inverted and the surface deep-etched and replicated. Examination in stereo of this composite preparation of two replicas with interposed half-membrane and associated surface elements reveals the physical relationship between structures on the surface and within the membrane. Composite replicas of the toad urinary bladder surface demonstrated connections of filamentous glycocalyx elements to intramembrane particles (IMPs). Using a bidirectional shadowing technique, many membrane surface particles also are shown to be associated with underlying IMPs, suggesting that these membrane surface particles are projections of the IMPs above the surface of the membrane. There is evidence that elements whose attachment sites relate to the half-membrane fractured away can be displaced from the membrane surface and lost. Labelling studies using colloidal gold-labelled antibodies were carried out to assess loss of surface mesh from fractured membrane. Gold distributions and amounts were similar in labelled surface replicas, label-fracture specimens, and labelled composite replicas, yet the amount of mesh detected in the composite replicas was less than in the surface replicas. This suggests that while some unlabelled or lightly labelled surface elements can be lost from fractured membranes, ligands stabilize elements and reduce their loss apparently by cross-linking them.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1060130308
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