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  • General Chemistry  (4,634)
  • Inorganic Chemistry  (3,506)
  • Cell & Developmental Biology  (2,672)
  • 1980-1984  (10,812)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0886-1544
    Keywords: motility ; power output ; muscle ; flagella ; cytokinetic furrow ; mitotic spindle ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cellular motile systems as diverse as muscle and the mitotic spindle have been compared by their specific power output: the maximum power they develop per unit of engine volume. Striated muscles and flagella have high specific output; their performance is comparable to that of typical automobile engines. The cytokinetic furrow and the mitotic spindle have very much lower specific power output. The furrow's output is 7,000 times lower than muscle and the spindle's is 300,000 times lower. Different macromolecules have been used to generate power in systems with similar output (muscles and flagella) and, conversely, the same macromolecular motor has been used in systems with very different output (muscles and cytokinetic furrows). The common feature amid this diversity is adaptation to a particular biological role, which specific power output reflects very well. High values are found where a powerful, compact engine should be advantageous, while low values are found where precision, not power, matters most.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 4 (1984), S. 41-55 
    ISSN: 0886-1544
    Keywords: Leptodiscinae ; Dinoflagellates ; contractility ; non-actin filaments ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The Leptodiscinae, a group of marine Dinoflagellates, are good material for the study of contraction though they cannot be collected in abundance. Their cell bodies are flattened anteroposteriorly (Leptodiscus, Leptophyllus, and Leptospathium) and are able to contract suddenly when the surrounding water is disturbed.Electron microscopical observations have shown that the structures responsible for the contraction consist of a layer of parallel filaments located beneath the cell membrane of some specialized parts of the body. These filaments seem to be nonactin (NAF) because of their diameter (2.5-3 nm) and because they are not decorated by heavy meromyosin (HMM). They appear helically coiled and doubly twisted, and form tubular structures when contracted.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 5
    ISSN: 0886-1544
    Keywords: fast axonal transport ; mitochondria ; membrane receptors ; cytoskeleton ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In living tissue, membrane-bound organelles, including mitochondria, move along parallel cytoplasmic pathways. Motion is directed and tends to be confined to a single path. Deviations from this single path motion are rare. When present, however, they tend to occur at points of intersection of cytoskeletal linear elements (LE). Such intersections are relatively uncommon in intact axons and extruded axoplasm. However, we have found that such intersections can be produced in extruded preparations by shear forces directed tangential to the axoplasmic surface.We have studied the detailed behavior of mitochondria in extruded squid axoplasm. Special attention was directed to the relationship between mitochondrial shape changes and orientation of cytoskeletal LE. The most striking of these changes in shape is branching. In this process, the mitochondrion transiently assumes a triradial (three-ended) shape. This appearance may be maintained for seconds to minutes before the normal cylindrical shape is resumed by absorption of either the newly formed end or, more commonly, one of the original ends. The frequency of branching appears to be dependent on the degree of cytoskeletal organization. It becomes more common as the number of apparent intersections between cytoskeletal LE increases. Further, the formation of new ends seems to occur along paths defined by cytoskeletal elements.These observations suggest that the mitochondrial membrane is multivalent. That is, it contains multiple sites capable of interacting with the axonal force generation apparatus. Furthermore, LE in the cytoskeleton may indicate the paths along which these interactions are permissible.
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  • 6
    ISSN: 0886-1544
    Keywords: axonal transport ; ATP ; nucleotides ; saltatory movement ; dynein ; video microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In a permeabilized axon model, exogenous ATP can reactivate intraaxonal saltatory organelle movements (microscopically visible manifestations of fast axonal transport). We have studied the dependence of the reactivated movements on the ATP concentration and have also examined the nucleotide specificity of the reactivation. Organelle transport was visualized in isolated lobster giant motor axons using Nomarski optics and video microscopy. The axons were permeabilized with saponin, and movement was reactivated with ATP or other nucleotides. Some slight movement was seen with ATP concentrations as low as 10 μM. The velocity and frequency of the reactivated transport increased with increasing ATP concentrations up to about 5 mM. Movement was also reactivated by deoxyadenosine triphosphate, but not by AMP-PNP (a nonhydrolyzable ATP analogue), ADP, or AMP. Although other nucleotides (CTP, GTP, UTP, ITP) could reactivate transport, movement equivalent to that produced by 0.1 mM ATP was only seen with tenfold or greater concentrations of the other nucleotides. This pattern of specificity is consistent with the hypothesis that a dynein-like ATPase, rather than a myosin, is involved in fast axonal transport.
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  • 7
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 8
    ISSN: 0886-1544
    Keywords: cytoskeleton ; motility ; cell spreading ; epithelial cells ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Reorganization of intermediate filaments during cell spreading is examined by immunofluorescence, electron microscopy, and time-lapse video microscopy. A juxtanuclear cap, believed to correspond to the intermediate filament distribution center, was observed to be spatially related to the organization of the intermediate filament network as cells spread. A keratin cap was observed, which appeared spontaneously in motile PtK1 cells. Cap formation may be a consequence of retraction of intermediate filaments from the cytoplasm as cells move. The position of this juxtanuclear cap is related to the direction of movement, located on the side of the nucleus near the advancing edge of the cell. As the cell spreads, the cap disappears as the keratin filament network returns to the cytoplasm. Evidence presented here is consistent with the hypothesis that the distribution center mediates keratin filament organization during cell shape change.
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  • 9
    ISSN: 0886-1544
    Keywords: sperm motility ; flagellum ; axoneme ; microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Iontophoretic application of ATP to the flagellum of the demembranated hamster spermatozoon produced a planar pair of bends at the two ends of the stimulated site. During bend propagation, torsion appeared in the vicinity of the interbend in some responses such that the distal bend was twisted clockwise when viewed from the base of the flagellum. This pattern of propagation is consistent with the instantaneous configurations of free-swimming cells previously described. The technique used here establishes that the three dimensionality arises from propagation per se, and does not depend on forces developed during swimming. The rolling of both free-swimming intact and demembranated spermatozoa was examined by two-color darkground videomicroscopy and the direction of rotation was, as predicted, always anticlockwise. A hypothetical mechanism, involving differential speeds of propagation of active sliding within the active microtubule subset, is proposed to account for the observed waveforms.
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  • 10
    ISSN: 0886-1544
    Keywords: cytoskeleton ; centrosome ; tonofilaments ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We present observations on the relative location of the centriole and keratin filament cap in motile PtK1 cells. Subconfluent cells were double labeled with anticentriole and antikeratin sera. These preparations revealed that the centriole is separate from, but neighboring, the keratin filament cap. Serial ultrathin sections confirm this observation. These observations are consistent with the idea that the microtubule organizing center and intermediate filament distribution center are not identical or concentric in PtK1 cells.
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  • 11
    ISSN: 0886-1544
    Keywords: microfilaments ; microtubules ; contraction ; collagen gel ; fibroblasts ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In vitro models have been developed recently to study the ability of fibroblasts to generate tensile force within collagen gels. The present study was initiated to assess the role of the cytoskeleton in the cell shape changes and force generation in one such model system. Porcine periodontal ligament fibroblasts (PPLF) were cultured within three-dimensional collagen gels attached to glass coverslips. Fluorescence microscopy, using nitrobenzooxadizole (NBD)-phallacidin labeling for microfilaments and tubulin antibody staining for microtubules, was combined with phase and Nomarski optics to determine the intra- and extracellular architecture of the cells and collagen fibers. Samples were observed from 30 minutes to 24 hours after initiation of cell attachment. During attachment and spreading, NBD-phallacidin staining changed dramatically until large microfilament bundles became prominent. Collagen fiber alignment, compaction, and finally tearing from the coverslip occurred during this time. After release of tension, microfilament bundles were no longer evident. The change in microtubule distribution during these processes was less dramatic, appearing to follow the change in cell shape. These results indicate that microfilaments play an essential role in generating force to align and compact collagen, while microtubules may have a secondary role only.
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  • 12
    ISSN: 0886-1544
    Keywords: Chlamydomonas ; flagella ; cell surface ; adhesion ; glycoproteins ; iodination ; lactoperoxidase ; Iodogen ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The Chlamydomonas flagellar surface exhibits interesting adhesive properties that are associated with flagellar surface motility. This dynamic surface property can be exhibited as the binding and movement of small polystyrene microspheres or as the interaction of the flagellar surface with a solid substrate followed by whole cell locomotion, termed “gliding.” In order to identify flagellar surface proteins that mediate substrate interaction during flagellar surface motility, two immobilized iodination systems were employed that mimic the conditions for flagellar surface motility: small polystyrene microspheres derivatized with lactoperoxidase, and large glass beads derivatized with Iodogen. Use of these iodination conditions resulted in preferential iodination of a high-molecular-weight glycoprotein with apparent molecular weight of 300,000-350,000. These results suggest this glycoprotein as a major candidate for the surface-exposed adhesive component that directly interacts with the substrate and couples the substrate to a system of force transduction presumed to be located within the flagellum.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 14
    ISSN: 0886-1544
    Keywords: taxol ; microtubules ; mitosis ; mitotic spindle ; calcium ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Taxol stabilizes or promotes the assembly of microtubules. In this report we characterize the rate, extent, and reversibility of taxol stabilization of calciumlabile microtubules in isolated mitotic spindles, principally from embryos of the sand dollar Echinarachnius parma. The intense depolymerizing action of 100 μM Ca2+ was used to assess the extent of stabilization by taxol. Changes in spindle microtubule assembly were evaluated and recorded by measuring changes in spindle birefringent retardation (BR). Membrane-free mitotic spindles, isolated with a calcium-chelating, nonionic detergent buffer, were stored in an EGTA-gylcerol storage buffer to prevent microtubule depolymerization. When perfused with an EGTA-buffer without glycerol, microtubules in these isolated spindles depolymerized gradually over 60-120 min; but in isolated spindles perfused with buffer that contained 100 μM Ca2+, BR decreased by 90% within 2-5 sec. In contrast, spindles that were pretreated for 3 min with 1 μM taxol, or for about 30 sec with 10 μM taxol, lost less than 10% of their initial BR when perfused with buffer containing 100 μM Ca2+. The rate and extent of microtubule stabilization by taxol depended on both the concentration and the duration of exposure to taxol. Taxol stabilization was reversible. After a 15 min preincubation with 1 μM or 10 μM taxol then washout, stability of spindle BR to 100 μM Ca2+ decreased exponentially with a time constant of 30-60 min. Thus taxol dissociates from spindle microtubules at significant rates; taxol-stabilized microtubules are not “fixed.”
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  • 15
    ISSN: 0886-1544
    Keywords: tubulin ; assembly ; mitotic apparatus ; bimane ; fluorescence microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Fluorescent derivatives of cellular proteins that retain their native characteristics have become useful probes to investigate the dynamics of specific cytoskeletal proteins. In the experiments reported here, a previously characterized fluorescent derivative of tubulin, bimane-tubulin [Wadsworth and Sloboda, 1982a], was used to investigate microtubule assembly in vitro. The results demonstrate that bimanetubulin was competent to assemble onto a variety of organizing centers in vitro, including microtubule organizing centers (MTOCs) present in homogenates of sea urchin eggs, isolated mitotic apparatuses (MAs), and lysed mitotic cells. When homogenates of fertilized sea urchin eggs containing MTOCs were incubated with bimane-tubulin at 37°C, discrete areas of linear fluorescence were observed. Only diffuse fluorescence was observed when calcium or colchicine was added to the homogenate or if the temperature was maintained at 0°C. Negative-stain electron microscopy of the fluorescent arrays revealed morphologically normal microtubules radiating from electron dense regions. When mitotic spindles, isolated in glycerol containing buffers and therefore cold stable, were incubated with bimane-tubulin, linear fluorescence was observed emanating from the spindle poles but not from the region occupied by the kinetochores. MAs incubated with bimane-labeled bovine serum albumin or bimane-labeled microtubule-associated proteins showed only diffuse fluorescence. However, when mitotic cells which were hypotonically lysed in the absence of detergents or microtubule stabilizing solvents, were perfused with bimane-tubulin intense fluorescence was observed in the asters and throughout the spindle. Two experiments suggested that the fluorescence observed in the results outlined above was due to the assembly of normal microtubules from the fluorescent subunits. First, the observed fluorescence was sensitive to cold temperataure, which is known to disassemble microtubules. Second, when the isolated, fluorescent MAs were examined by thin section electron microscopy, microtubules of normal diameter were seen. No aggregated material appeared associated with the walls of the microtubules, which might have been expected if the fluorescent protein was nonspecifically adsorbed to the microtubules. The results of these experiments demonstrate that isolated, stabilized MAs support the growth of new microtubules from the spindle poles while labile spindles, present in lysed cells, incorporate fluorescent tubulin throughout the spindle and asters. The significance of these results for hypotheses concerning microtubule assembly and disassembly during mitosis is discussed.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 17
    ISSN: 0886-1544
    Keywords: axonemal mutants ; Ca++ response ; ciliary reversal ; electrophysiology ; models ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Six mutants of Paramecium tetraurelia, which display altered axonemal responses to Ca++, are described. The mutants, designated atalantas, are impaired in their ability to swim backward when stimulated by ions or heat; instead they spin very rapidly in one place. Three mutants, ataA1-3, are completely unable to swim backward. The three lines, however, can be distinguished from one another by their forward swimming velocities. The remaining three mutants are leaky. ataB swims backward briefly when stimulated, then stops and spins in place. ataC and ataD are extremely leaky and only display the spinning phenotype at elevated temperatures. An electrophysiological analysis reveals that all six mutants have normal membrane properties, including the Ca++ inward current under voltage clamp. When the membrane is disrupted so as to allow the axoneme free access to Ca++, wild-type cells swim backward, but the mutants do not. These data indicate the site(s) of lesion in the mutants is in the axoneme or in some step linking Ca++ influx and the axoneme, not within the ciliary membrane. These mutants may be useful in investigating the role of Ca++ in the regulation of axonemal motion.
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 4 (1984), S. 305-314 
    ISSN: 0886-1544
    Keywords: cell surface motility ; axopodia ; reticulopodia ; Allogromia ; Echinosphaerium (Actinosphaerium) nucleofilum ; surf-riding ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The mechanism responsible for the energy-dependent movement of membrane components (ie, surface motility) is unknown. Recently a potentially unifying model, termed “surf-riding” [Hewitt, 1979] or “surf-boarding” [Berlin and Oliver, 1982], has been proposed to explain surface motility. Using phase-contrast light microscopy and membrane surface markers (polystyrene microspheres), we have tested the surf-riding/surf-boarding hypothesis on two protozoan systems: the axopodia of the heliozoan Echinosphaerium nucleofilum and the reticulopodial networks of the allogromiid foraminiferans Allogromia laticollaris and Allogromia sp, strain NF. Our evidence indicates that surface motility, as displayed by these organisms, does not occur by a surf-riding/surf-boarding mechanism. Previouś observations on surface motility associated with the Chlamydomonas flagellum indicate that this system is also incompatible with the surf-boarding/surf-riding hypothesis.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 4 (1984), S. 403-404 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 4 (1984), S. 469-503 
    ISSN: 0886-1544
    Keywords: cytogel ; actomyosin ; Physarum ; oscillations ; mechanics ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The contractility of actomyosin gels is the basis for a variety of cellular motility phenomena. We present here a mechanical analysis of contractile gels. By making certain hypotheses on the chemical regulation of cytogel contraction we formulate a model for the rhythmic contractions of plasmodia in the slime mold Physarum polycephalum which is in accord with a number of experimental observations.
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  • 21
    ISSN: 0886-1544
    Keywords: cilia ; metachrony ; serum immunoglobulins ; IgM ; Mytilus edulis ; cystic fibrosis ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Human IgM and a bovine, IgM-enriched serum fraction isolated from normal adult serum at concentrations of 0.25-1 mg/ml protein induced a pronounced increase in the metachronal wavelength of the lateral (L) cilia of the sea mussel Mytilus edulis without altering their beat frequency. This change in activity was indistinguishable from that induced by 50% adult human or bovine serum. At protein concentrations ranging from 1-9 mg/ml, human IgG or a bovine, IgG-enriched serum fraction had no or little effect on the activity of the L cilia. Similarly, neither monomeric (8S) human IgM (0.25 mg/ml) nor monospecific pentameric IgM (1 mg/ml) isolated from Waldenström's macroglobulinemia patients altered the metachrony of the L cilia. Indirect immunofluorescence demonstrated that both bovine and human IgM became attached almost exclusively to the L cilia, while very little bovine or human IgG was found to associate with these cilia.The results of this study suggest that serum IgM specifically binds to the L cilia of Mytilus in an antigen-antibody manner and agglutinates adjacent cilia into blocks or bundles, thereby increasing the coupling between cilia. As a result, the wavelength of the metachronal coordination is increased. The origin of these ciliary antibodies and their significance to ciliary bioassays used to monitor serum for the detection of cystic fibrosis are discussed.
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  • 22
    ISSN: 0886-1544
    Keywords: axoplasm ; elastic modulus ; viscosity ; motility ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A magnetic sphere viscoelastometer has been developed to peform rheological experiments in living axoplasm of Loligo pealei. The technique includes the use of a calibrated magnetic sphere viscoelastometer on surgically implanted ferro-magnetic spheres in intact squid giant axons. The axoplasm was discerned to be “living” by the biological criterion of tubulovesicular organelle motility, which was observed before and after experimentation. From these in vivo experiments, new structural characteristics of the axoplasm have been identified. First, analysis of magnetic sphere trajectories has shown the axoplasm to be a complex viscoelastic fluid. Directional experimentation showed that this material is structurally anisotropic, with a greater elastic modulus in the direction parallel to the axon long axis. Second, both magnetic sphere and in vivo capillary experiments suggested that the axoplasm is tenaciously anchored to the axolemma. Third, it was found that axoplasm could be modelled as a linear viscoelastic material in the low shear rate range of 0.0001 to 0.004 s-1. The simplest mechanical model incorporating the discovered properties of the material in this range is Burger's model.
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  • 23
    ISSN: 0886-1544
    Keywords: Paramecium ; trifluoperazine ; cilia ; calmodulin ; calcium ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Trifluoperazine (TFP), a drug that binds to Ca2+-calmodulin (CaM) complexes, altered swimming behavior not only in living paramecia, but also in reactivated, Triton-extracted “models” of the ciliate. By comparing the responses of living cells and models, we have ascertained that two sites of drug action exist in paramecium cilia. Swimming movements were recorded in darkfield stroboscopic flash photomicrographs; this permitted accurate quantitation of velocities and body-shape parameters. When living paramecia were incubated in a standard buffer containing 10 μM TFP, their speed of forward swimming fell over several minutes and their bodies shortened. Untreated paramecia backed up repeatedly and frequently upon transfer to a solution containing barium ions (the “barium dance”), but cells preincubated in TFP did not “dance.” Instead they swam forward slowly for long periods of time without reversing and occasionally then exhibited abnormally prolonged reversals. W7 effects on swimming mimicked low doses of TFP, and the analog W5 did not visibly alter normal swimming patterns. These results suggest that TFP induces a decrease in the intracellular pCa of living paramecia, perhaps by reducing the efficiency of a calmodulin-activated calcium pump in the cell membrane. Paramecia extracted with Triton X-100 and reactivated to swim forward (7 ≥ pCa ≥ 6) were not affected by addition of up to 40 μM TFP to the reactivation medium. We conclude that the main drug effect in living cells is probably not at the axoneme. However, at low pCa, TFP directly affected the ciliary axoneme to shift its behavior to one characteristic of a higher pCa: TFP inhibited backward swimming in models reactivated at pCa 〈 6; instead they swam forward or rocked in place. The mechanism of ciliary reversal in paramecium may therefore depend on an axonemal Ca+-sensor, possibly bound CaM, which is affected by TFP only at low pCa, as has been postulated for other types of cilia.
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  • 24
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 25
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 4 (1984), S. 351-370 
    ISSN: 0886-1544
    Keywords: axon ; rate ; nervous system ; tissue culture ; cell growth ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A new formula calculates rates of directed axonal growth (elongation or retraction) using measurements of growth cone movements. By explicitly separating changes in axonal length from other nonelongational growth cone movements, the calculated rates reflect the detailed cellular growth mechanisms more directly than previous growth measures. In addition, the formula produces three distinct parameters of axonal elongation: n, a growth step rate; s, a growth step size; and P, a probability that a growth step leads to axonal elongation. For normal and regenerating individual chick and frog axons in culture, the formula has quantitated the following differences: the axon itself can elongate more rapidly in the chick, and the axon elongates in smaller steps in the chick. The underlying dynamics of growth of regenerating axons are quite similar to normal axons, but, in the short term, regenerating axons elongate in larger steps and at a slower rate. The distribution of these new rate measurements suggests that the elongation of axons can be usefully modelled as a one-dimensional stochastic walk.
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  • 26
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 4 (1984), S. 371-385 
    ISSN: 0886-1544
    Keywords: microtubules ; dynein ; tubulin ; cilia and flagella ; microtubule associated proteins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Dynein, obtained from axonemes of Chlamydomonas, binds by both its A and B ends to microtubules assembled from twice cycled (2 ×) and purified (6S) brain tubulin as well as to microtubules in native spindles, thereby inducing microtubule crossbridging. The two ends of the dynein arm exhibit distinct binding characteristics for the different microtubule preparations. Greater than 99% of the dynein arms are bound exclusively by their B ends to microtubules assembled from 6S tubulin in the presence of dynein and decorated to saturation. In contrast, greater than 80% of the dynein arms are bound by both their A and B ends to and, therefore, crossbridge 6S microtubules that are only partially dynein decorated. Binding of the A end of the dynein arm to saturated 6S microtubules can be enhanced by destabilizing the binding of the B end upon addition of ATP and vanadate. These observations suggest that Chlamydomonas dynein arms can bind by their A ends to microtubules assembled from 6S tubulin only when the B ends of the arms either are not bound or are bound but do not occupy all available dynein binding sites. Dynein exhibits a slight preference for binding by its A end to microtubules assembled from 2 × tubulin and containing microtubule associated proteins (MAPs). Approximately 90% of the dynein arms crossbridge adjacent 2 × microtubles that are only partially decorated. But as saturation of these microtubules with dynein is approached, the majority of the arms are bound solely by their A ends, while a smaller percentage are bound by their B ends or by both their A and B ends. These studies indicate that the type of microtubule as well as the degree of saturation of the microtubule with dynein can determine whether microtubule crossbridging occurs.
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  • 27
    ISSN: 0886-1544
    Keywords: actin ; microfilaments ; HMM ; phagocytosis ; cytochalasin ; Paramecium ; fluorescence microscopy ; electron microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Using heavy meromyosin (HMM) or the fragment S1 of myosin as probes for actin microfilaments, we studied their organization in Paramecium both by fluorescence and electron microscopy.In interphasic cells, HMM decorates (a) most prominently the periphery of nascent and young food vacuoles and their route during the early phase of their intracellular transit; (b) a thin meshwork radiating from the gullet throughout the cytoplasm; (c) a small area beneath the pore of contractile vacuoles and beneath the cytoproct when open to release food residues. Most of these HMM-decorated structures are in close contact with microtubular arrays. All HMM decoration disappears in dividing cells and in cytochalasin-treated cells. In vivo, the drug immediately blocks food vacuole formation but does not affect cytokinesis, cyclosis, contractile vacuole pulsation, defecation, or nuclear movements.The data show that, as in the cells of other organisms, actin microfilaments form defined arrays that undergo physiologically controlled cycles of assembly/disassembly. These arrays contribute (at least in the phagocytotic process) to diverse types of movement: constriction, membrane fusion, and migration of food vacuoles. However, aside from their massive concentration along the phagocytotic tractus, actin microfilaments are neither major structural components of Paramecium cytoplasm nor the only cytoskeletal components ensuring motility or contractility processes.
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  • 28
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    Cell Motility and the Cytoskeleton 4 (1984), S. 431-441 
    ISSN: 0886-1544
    Keywords: dynein ; chromatophores ; permeabilization ; melanosomes ; motility ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Teleost chromatophores are filled with individual pigment granules that rapidly aggregate to the cell center or become dispersed throughout the cytoplasm in response to environmental stimuli. Microtubules appear to be required for pigment aggregation (movement toward the cell center), and recent findings have suggested that a dynein-like ATPase may participate in force production. Based on previous studies, however, it has been argued that pigment aggregation does not require energy directly, a view that supports the involvement of an elastic component in granule movement. To examine this point further, we have reinvestigated the energy requirements for pigment aggregation using both intact cells and detergent-permeabilized cell models of Fundulus melanophores. Poisons of oxidative phosphorylation, namely, 2,4 dinitrophenol and NaCN, reversibly inhibit melanosome aggregation in response to adrenaline. Inhibition of movement results directly from depletion of intracellular ATP, since pigment translocation can be reactivated in permeabilized cells by the addition of exogenous ATP to the lysis buffer. Non-hydrolyzable analogues, including β,γ-imidoadenosine-5′-triphosphate (AMPPNP), β,γ-methylene adenosine-5′-triphosphate (AMPPCP), and ATPγS, will not substitute for ATP in reactivation of movement. Similarly, other nucleotides such as ADP, AMP, GTP, CTP, and ITP, have limited ability to support melanosome aggregation in metabolically poisoned cells subjected to detergent lysis. ATP itself has no effect on intact cells. These results indicate that melanosome aggregation is ATP-dependent and energy-driven, and are consistent with a role for a force-transducing ATPase in particle movement.
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  • 29
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 30
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    Cell Motility and the Cytoskeleton 4 (1984), S. 76-76 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 31
    ISSN: 0886-1544
    Keywords: actin ; calcium ; coelomocytes ; ionophore ; pH ; shape transformation ; video microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have investigated the ability of the Ca+ + ionophore A23187 to induce the transformation of petaloid sea urchin coleomocytes to the filopodial form. The response of individual cells to different media was observed with time-lapse phasecontrast video microscopy. In the presence of 1 mM CaCl2, isotonic medium containing 1-5 μM A23187 produces a similar shape transformation to that caused by hypotonic shock. Higher concentrations of ionophore (10-20 μM) induce the formation of filopodia that are thinner and less rigid than those generated by hypotonic shock or low doses of ionophore. A23187 also induces shape transformation in highly flattened cells that do not respond fully to hypotonic shock. The induction of cytoplasmic alkalinization by NH4Cl, methylamine-HCl, or the Na+ ionophore monensin does not induce shape transformation, suggesting that increased intracellular pH is not the stimulus for this process. Ultrastructural changes in cytoskeletal organization were examined in negatively stained detergent-extracted cells. Low doses of ionophore produce filopodia that are indistin-guishable from those of hypotonically shocked cells, with actin filament bundles that are straight and cohesive along their entire length. High concentrations of ionophore produce filopodia with filament bundles that branch repeatedly and splay apart near their tips, forming loops and irregular curves. These results suggest that an increase in intracellular free Ca+ + concentration acts as the trigger that stimulates coelomocyte shape transformation, but that abnormally high concentrations of intracellular Ca+ +, produced by high doses of ionophore, interfere with actin filament bundling.
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  • 32
    ISSN: 0886-1544
    Keywords: gelation ; actin ; filamin ; cytoplasm ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have compared the meniscus depletion assay and falling ball viscometry, two means of assessing the extent of gelation in actin-based systems using mixtures of actin and the actin-binding protein filamin. We examined the effect of varying the concentrations of actin and filamin in both assays. The interaction of actin and filamin was detected only above a threshold concentration of filamin. This threshold concentration was lower for falling ball viscometry than for the meniscus depletion assay at equal actin concentrations. At constant concentrations of filamin, an increase in actin concentration caused an increase in apparent viscosity measured by the falling ball assay, but a decrease in sedimentability detected by the meniscus depletion assay. The rate of sedimentation of actin was dependent on the molar ratio of actin to filamin. At each molar ratio, the sedimentation of actin was not dependent on the specific concentrations of actin and filamin used. The apparent viscosity was dependent on both the molar ratio and the specific concentrations of actin and filamin. To relate the present results to earlier studies, we examined mixtures of actin and filamin using a macroscopic assay of gelation (tube tipping assay), and polarized light microscopy. The effect of increasing filamin concentration in the four assays was compared at three actin concentrations. Mixtures of actin and filamin whose apparent viscosities were low enough to be estimated by falling ball viscometry were optically isotropic fluids that flowed out of inverted test tubes. Mixtures of actin and filamin in the range of sensitivity of the meniscus depletion assay were either viscous fluids or gels, and were either optically isotropic or anisotropic. Thus, the four assays provide different estimates of gelation. Both the meniscus depletion assay and falling ball viscometry can be used to determine relative gelation activity, but neither can be used as a quantitative assay of gelation.
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  • 33
    ISSN: 0886-1544
    Keywords: microtubules ; microfilaments ; filopodia ; cell spreading ; coelomocytes ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Sea urchin coelomocytes were used as a model system to investigate the distribution and role of microtubules and microfilaments in cell spreading and filopodial formation. By using immunoblot characterized antisera to tubulin and actin coupled with immunofluorescence techniques, cellular protrusions were seen to contain actin filaments but no microtubules. Cells depleted of MT's by cold and colcemid treatments could attach, spread, and transform to the filopodial morphology normally.
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  • 34
    ISSN: 0886-1544
    Keywords: pseudostereoscopy ; particle speed distribution ; velocity distribution ; fast axonal transport ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We describe a simple method for direct visualization of the velocity distribution of particles moving against an immobile background. The technique involves pseudostereoscopic viewing of image pairs separated by an appropriate time interval in a sequential recording of the subject. Under these conditions, the positive or negative parallax arising from particle motion results in the binocular image of a particle being perceived as raised or lowered relative to an immobile background plane depending on its direction of movement, and with the degree of perceived elevation being proportional to its speed. In effect, the binocular optic axis becomes a velocity (speed) axis under these conditions. The technique is illustrated with examples of image pair sequences showing fast axonal transport in lobster and squid axons using video-enhanced differential interference contrast microscopy. However, the pseudostereoscopic method is quite generally applicable to both microscopic and macroscopic time-dependent phenomena. Particle speeds can be quantitated using standard procedures for measuring frame-to-frame particle displacements, or alternatively, by determination of parallax using stereogrammatic methods. It should be also readily adaptable for on-line monitoring of particle velocity distribution, particularly in video systems where frame buffers can be utilized to extract and present serial image pairs having any desired time separation from video-taped sequences.
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  • 35
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    Cell Motility and the Cytoskeleton 4 (1984), S. 304-305 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 36
    ISSN: 0741-0581
    Keywords: Immunocytochemistry ; Protein A-Gold ; Lowicryl ; Glycolmethacrylate ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The postembedding protein A-gold immunocytochemical approach has been introduced as an alternative to other techniques for the ultrastructural localization of antigenic sites. The present review deals with the development, the theoretical background, and technical approach of the protein A-gold method as well as the different modifications introduced in order to enhance the resolution of the results and to perform double labelings on the same section. Various examples demonstrate the reliability and the wide range of application of this technique. In addition, some problems, pitfalls, and limitations particular to this method are reported.
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  • 37
    ISSN: 0741-0581
    Keywords: Vascular cell cultures ; Transmission electron microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: A method is described for obtaining optimal, reproducible ultrastructure of vascular smooth muscle cells and vascular endothelial cells in culture. Routinely grown cultures are prepared for TEM with a precise regimen of fixation, postfixation, en bloc staining, dehydration, and embedment. The most important aspects of this procedure are the following: (1) fixation with a percentage-gradient series of glutaraldehyde solutions at 37°C, (2) immediate postfixation with osmium tetroxide solution, and (3) block-staining with uranyl acetate solution to eliminate any extraction of constituents during subsequent processing.
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  • 38
    ISSN: 0741-0581
    Keywords: Monolayer cells ; preparation for SEM ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Monolayers of PtK-1 and HeLa cells grown on glass or plastic supports are extremely susceptible to lacerations, e.g., splits and cracks caused mainly by shrinkage when prepared for scanning electron microscopy (SEM). We find that a four-step fixation procedure including glutaraldehyde, OsO4, tannic acid, and uranylacetate application, in combination with critical point drying, drastically reduces these structural damages. In addition, the conductivity of the specimens is enhanced, so that they can be investigated without gold coating. Transmission electron microscopy (TEM) investigation of perpendicular sections in the area of lacerations provides evidence that the subcortical cytoskeletal elements are of crucial importance in maintaining cell membrane stability during the preparations. Our relatively quick and simple procedure results in an improved structural appearance of the cells.
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  • 39
    ISSN: 0741-0581
    Keywords: Opioids ; Receptors ; Brain ; Radioautography ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Two met-enkephalin analogs (FK 33-824 and FW 34-569, Sandoz) were utilized for in vitro labeling of opioid binding sites in the rat central nervous system. Binding kinetics determined in 20-μm-thick frozen tissue sections of the striatum revealed that both pentapeptides bind to a single population of sites at 20°C with an apparent dissociation constant (KD) of approximately 1-2 nM and a maximum capacity (B max) of 65-170 fmoles/mg protein. Radioautographic data suggest that this population is the same for iodinated and tritiated forms of the FK compound and the iodinated FW analog. Fixation of labeled sections with high concentrations of glutaraldehyde allowed proportional retention of more than 50% of specifically bound 125I-FK molecules in all brain regions after histological processing for high-resolution radioautography. In contrast, glutaraldehyde fixation did not prevent the loss of bound 125I-FW molecules. These differences are attributed to the presence in FK, but not in FW molecules, of a free primary amino group considered essential for cross-link formation between aldehydes and proteins, and imply that a majority of FK-receptor complexes may be stabilized by glutaraldehyde. Consistent with this observation is the fact that the radioautographic distribution of specifically bound 125I-FK was unchanged after fixation and dehydration. In electron microscopic radioautographs prepared from prefixed, vibratome-cut striatal sections that were incubated with 125I-FK and fixed with glutaraldehyde, silver grains were found to be mostly associated with neuronal plasma membrane interfaces. The present methodological approach thus appears to be compatible with electron microscopic localization of opioid binding sites in the central nervous system and might be applicable to the localization of other types of binding sites using radioligand molecules that contain a free primary amino group.
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  • 40
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    ISSN: 0741-0581
    Keywords: Ceramics ; Electron microscopy ; Ion milling ; Specimen preparation ; Sputtering ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Ion bombardment to perforation is a common technique in the materials sciences by which thin specimens can be prepared for transmission electron microscopy. The process is not without complication and involves radiation damage to the specimen and tends not to preserve the initial specimen topology. Some of the more important facets of the ion-milling process, pertinent to such specimen preparations, are described.
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  • 41
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
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  • 42
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
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  • 43
    ISSN: 0741-0581
    Keywords: Particle size ; Electron microscopy ; Microcomputer programs ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: A formula is derived to enable the calculation of the true height of an object, such as a shadowed latex bead, from electron micrographs. Knowing only the angle of shadowing and the length of the evaporated shadow, and by substituting these values in the derived formula, a microcomputer may be programmed to carry out the necessary computations. An example of such a microcomputer program is given. The correct determination of the height of particles by electron microscopy using the shadowing technique is one of the most accurate methods available for the determination of small particle height.
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  • 44
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
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  • 45
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    ISSN: 0741-0581
    Keywords: Scanning transmission electron microscopy ; Image contrast ; Inelastic scattering ; Thick specimens ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: For scanning transmission electron microscopy (STEM) images obtained with relatively small objective aperture sizes, the contrast of small objects contained within thick specimens may be considerably enhanced by using an off-axis detector aperture situated on the edge of the central beam spot. The effect is demonstrated for both crystalline and amorphous specimens. The effect arises because the detector collects part of the small angle inelastic scattering and is modified by refraction effects for specimens of rapidly changing thickness.
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  • 46
    ISSN: 0741-0581
    Keywords: GACH ; Amino-resin ; SEM ; Preparation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Biological specimens can be prepared for scanning electron microscopy by means of copolymerizing the fixing agent glutaraldehyde with carbohydrazide prior to air drying. Such preparations are more stable in the electron microscope, show less internal cellular disruption and retain more of their native elemental composition than specimens prepared by means of dehydration and critical-point drying. Specimens observed in the scanning electron microscope can often be recovered for thin sectioning with no additional embedment, and can then be observed by means of transmission elecltron microscopy. The preparation (termed GACH) can be performed in almost any laboratory with no specialized equipment and, for the most part, may be carried out at room temperature. The technique appears to provide the promise of further research applications in scanning electron microscopy which may employ conjugated procedures of immunocytochemistry and cathodoluminescence as well as X-ray microanalysis in limited situations.
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  • 47
    ISSN: 0741-0581
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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  • 48
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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  • 49
    ISSN: 0741-0581
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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  • 51
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    Keywords: Vascular casts ; Scanning electron microscopy ; Vascular anatomy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Corrosion casts provide three dimensional replicas that can be examined readily by scanning electron microscopy (SEM). They are prepared by filling vascular networks with polymerizing plastic and then digesting away the tissue. As based on our studies of ocular vessels, this report describes the vascular anatomy, as well as the artifacts, that are encountered during SEM studies of such preparations.
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  • 52
    ISSN: 0741-0581
    Keywords: TEM ; Parallax equation ; Freeze-etch ; Pt-C replication ; Hydrated spermidine-condensed DNA toruses ; Stereoheight measurements ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Stereoimaging of hydrated single complex macromolecules requires thin freeze-etch platinum-carbon replicas (≤200 Å) and that the transmission electron microscope (TEM) be equipped with a tilt-rotation eucentric goniometer stage. The original parallax equation is an accurate approximation for high-magnification work, micrographs (105 ×) being less than 0.3% in error. In addition, we have derived formulas for high-magnification work to measure heights, lateral distances, and the object tilt angle for an object not lying flat on the film surface. The accuracy of the height measurements is evaluated on spermidine-condensed DNA toruses. By using the maximum error equation derived from the original parallax equation, we discuss methods to improve the height measurement precision (95% fractile) to the 5-10 Å range.
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  • 53
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    Keywords: Ultramicrotomy ; Serial sectioning ; Electronmicroscopy ; Seria reconstruction ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The process of serial sectioning for electron microscopy has been refined such that loss of thin sections is kept below 0.1% and the series is continued at will. The method relies on microscopic control of all manipulative steps, Formvar casting on plate glass for coated slot grids, coating of the block with contact cement for reliable ribboning, pickup by a one-step method with grid support in the diamond knife trough, staining in LKB grid holders, gentle treatment of grids in the electron microscope, and a slight modification to the microscope for safe grid withdrawal. The results are particularly applicable to the reconstruction of neuronal microcircuits and larger volumes of neuropil.
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  • 54
    ISSN: 0741-0581
    Keywords: Enzyme-gold ; Cytochemistry ; Nucleic acids ; Elastin ; Collagen ; Glycogen ; Xylans ; Chitins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The enzyme-gold postembedding approach has been introduced recently in the field of cytochemistry for the ultrastructural localization of macromolecules. This technique is based on the affinity properties existing between an enzyme and its substrate. The possibility of detecting substrate molecules by applying enzyme-gold complexes has been established. The present review deals with the development and the technical approach of this method. Various applications are reported for the demonstration of the reliability of the technique that yields results of high specificity and resolution. In addition, some technical problems and limitations particular to this method are reported and discussed.
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  • 55
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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  • 56
    ISSN: 0741-0581
    Keywords: Quick freezing ; Synaptic vesicles ; Cholinergic nerve terminals ; Electric organ ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The limitations of chemical fixation in permitting the 1:1 quantitative correlations required for convincing ultrastructural explanations of cell biological processes are noted. We describe techniques for obtaining highly reproducible direct quick freezing on the polished surface of pure copper bars dipping into a static dewar of liquid N2. The importance and the ease of testing and obtaining bounce suppression with commerically available equipment is emphasized. Artefacts caused by tissue damage and bad freezing are illustrated, and a hitherto unrecognized population of presynaptic membrane attached vesicles is described in Torpedine electric organ. Between 15 and 20% of the synaptic vesicles are attached to ca. 30% of the cytoplasmic face of the presynaptic terminal membrane. There is a close correlation between the occurrence of such attachments and the application of electrocyte basal lamina to the external face. We suggest that these vesicles are the ‘membrane operators,’ ‘vesigates,’ and ‘highly active subpopulation’ of vesicles whose existence has been invoked to explain biochemical data in other laboratories. We further speculate that relatively selective Ca pumping by this immediately submembranous population leads to displacement of acetylcholine (ACh) and reloading with newly synthesized ACh. The preferential release of the latter would then be expected.
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  • 57
    ISSN: 0741-0581
    Keywords: Cross-section specimen ; Thin films ; Interfaces ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The structure and chemistry of thin solid films are best studied by transmission electron microscopy (TEM) when they are viewed in cross-section - that is, when the surface normal of the film is made perpendicular to the electron beam. In this orientation, the substrate, the thin film layers, and the interfaces between them can be imaged either simultaneously or individually. Further, information from each of these regions remains distinct from that obtained from the others, eliminating the problems of superimposition that are a consequence of viewing a layered structure in the conventional manner (i.e., parallel to the surface normal). A technique for fabricating TEM specimens that can be viewed in cross-section is described here. Although the majority of our work is with silicon-based materials, the technique can be readily adapted to the study of other systems.
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  • 58
    ISSN: 0741-0581
    Keywords: Photography ; Point source enlarger ; Electron micrograph ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Point source enlargers may cause unusual types of printing defects. One type is a large spot in the center of the enlarged picture field that sometimes appears when the edges of negatives are not adequately masked during printing. Another type is a blurry image caused by a defect in the polycontrast filter. The defect appears in the filter as a small spot of about 1/8-inch diameter, formed, presumably, by heat from the focused beam of the point source light. A spot defect of this type is difficult to see by a cursory visual examination of the filter and may develop unnoticed and persist for months before it is finally recognized.
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  • 59
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    ISSN: 0741-0581
    Keywords: Electron energy loss spectroscopy ; Parallel detection ; Photodiode assays ; Fluorescent screens ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: The present report paper deals with the use of a photodiode array for recording electron energy loss spectra in a transmission electron microscope. Important properties of the array are outlined, together with a description of the circuitry needed for interfacing the output to a multichannel analyser.In the direct-exposure mode, the device can easily detect a single (80 or 100 keV) electron, allowing inner-shell energy losses between 200 eV and 2000 eV to be recorded in about 10 seconds. By signal averaging a large number of readouts, a dynamic range of at least 105 is possible. Irradiation damage to the array can be controlled by cooling the array and by various anealing procedures. Sensitivity and DQE are lower, but the dynamic range is higher in the indirect mode, where a fluorescent screen is used to convert the electrons into visible photons, which are then imaged onto the diodes. The choice of screen material and of optical coupling to the array are discussed. Several spectral artifacts are described, together with spectrum-processing techniques designed to remove them.
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    ISSN: 0741-0581
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 61
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0741-0581
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 62
    ISSN: 0741-0581
    Keywords: Cardiac muscle ; Rapid freezing ; Cryosectioning ; X-ray microanalysis ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Electrically stimulated heart muscle preparations can be quickly frozen in undercooled propane at defined times of the mechanically controlled contraction cycle. The apparatus for triggered freezing of the muscle strips in undercooled propane is described in detail. Freeze substitution of some strips after freezing shows the degree of ice crystal formation without the potential interference of artifacts introduced later by cryosectioning and freeze drying. Ultrathin longitudinal and transversal cryosections are cut with a LKB cryoultramicrotome at temperatures of -130 to -140°C, freeze-dried at 10-6 Torr vacuum and carbon-coated before analysis. The freeze-dried cryosections are analyzed in a Siemens Elmiskop 102 electron microscope equipped with a Kevex energy dispersive system, and the elemental concentrations (in mMol/kg d.w.) of Na, Mg, P, S, Cl, K, and Ca are determined in subcellular compartments of muscle frozen in different functional states. The methodology of quantitation, i.e, determination of elemental net peak and continuum, correction of continuum, preparation of standards, and deconvolution of overlapping peaks are described. The minimum detectable elemental concentration using the reported methods is in the range of a few mMol/kg d.w. This also applies to Ca, which can be accumulated in heart muscle in readily detectable amounts in intracellularly located stores as well as structures connected with the cell membrane. The present report shows that cryotechniques and x-ray microanalysis can be successfully applied to heart physiology.
    Additional Material: 18 Ill.
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  • 63
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0741-0581
    Keywords: Critical point drying ; Electron microscopy ; Ultrastructure ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000