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  • 1
    Electronic Resource
    Electronic Resource
    Electro-acoustic fusion of cells (1985)
    Springer
    Naturwissenschaften 72 (1985), S. 441-442 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00404895
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  • 2
    Electronic Resource
    Electronic Resource
    Real time observations of polylysine, dextran and polyethylene glycol induced mutual adhesion of erythrocytes held in suspension in an ultrasonic standing wave field (1987)
    Springer
    European biophysics journal 14 (1987), S. 499-507 
    Details
    ISSN: 1432-1017
    Keywords: Erythrocyte ; cell adhesion, cell agglutination ; acoustic radiation force ; ultrasonic levitation ; interfacial instability ; polylysine ; dextran ; polyethylene glycol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A technique which enables cells to be observed in suspension for times of the order of minutes (employing acoustic radiation foreces in a 1 MHz ultrasonic standing wave field) is described. Video recordings of the mutual adhesion of human erythrocytes in suspension have been analysed. Concave-ended cell doublets and linear rouleaux developed in 0.5–1.5% w/v Dextran T500 by a gradual (2.5–17 s) increase in the area of cell contact over the cell cross-section. The concave-ended rouleaux form was not seen in polylysine or in polyethylene glycol. In 5–7% dextran and in 20μg/ml polylysine mutual adhesion was a two stage process. Cells first form a strong local contact which persists (without apparently growing in area) for a number of seconds following which the cell surfaces move suddenly to form a spherical doublet. The average initial contact time and engulfment time for cells in 7% Dextran T500 are 18 and 2.7 s, respectively. The corresponding values for cells in 20 μg/ml, 14 kDa, polylysine are 2.7 and 0.3 s. There was no initial contact delay during spherical doublet formation in mg/ml polylysine. Electron microscopy showed that the intercellular seam for spherical doublets formed with all three agglutinating molecules was bent in a wavy (λ∼4 μm) profile. The thickness of the intercellular space varied in a spatially periodic way (λ∼0.8 μm) for cells in polylysine. Examples of periodic intercellular spaces were seen by light microscopy in polyethylene glycol induced clumps. The role of interfacial instability in the adhesion processes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00293260
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  • 3
    Electronic Resource
    Electronic Resource
    Interfacial instability and the agglutination of erythrocytes by polylysine (1985)
    Springer
    European biophysics journal 13 (1985), S. 123-130 
    Details
    ISSN: 1432-1017
    Keywords: Erythrocyte ; interfacial instability ; surface wave ; polylysine ; cell agglutination ; cell adhesion, acrosome reaction ; membrane fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Human erythrocytes have been exposed to poylysine of molecular weight range 4 to 220 kDa and concentration range 0.5 to 2,000 μ/ml at 37°C. Threshold concentrations for cell agglutination by the polycation have been determined for the samples of different molecular weight. Light and electron micrographs show that, in the erythrocyte agglutinates, cell-cell contact is generally made only at discrete, spatially periodic, regions which are distributed over a significant part of the cell surface. The average spacing between contact regions is 0.83 μm. The cell membrane has a wavy profile between contact regions. Agglutination occurs only in cell samples whose electrophoretic mobility is significantly altered by polylysine and, in agreement with a previous report, occurs even when the electrophoretic mobility reaches high positive values. The electrophoretic mobility data implies that agglutination requires some protrusion of polylysine from the cell glycocalyx. We discuss how a resulting net attractive intercellular force could act to destabilize the aqueous layer between two cells, allowing surface wave growth which results in spatially periodic contact regions. Examples of situations where cell and membrane contact might be explained by the general concept of interfacial instability are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00256532
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of polymer concentration and molecular weight and of enzymic glycocalyx modification on erythrocyte interaction in dextran solutions (1993)
    Springer
    European biophysics journal 22 (1993), S. 53-62 
    Details
    ISSN: 1432-1017
    Keywords: Cell adhesion ; Dextran ; Erythrocyte adhesion ; Membrane fusion ; Interfacial instability ; Fluid film instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Erythrocytes adhere to each other when suspended in supra-threshold concentrations of dextran of molecular mass of 40 kD or greater. The plasma membranes are parallel to each other over the entire length of the contact seam at the lower effective polymer concentrations. When cells are pretreated with the proteolytic enzyme pronase or the sialidase neuraminidase the membranes are not parallel but make contact at spatially periodic locations along the membrane surface. Pronase induced reduction of cell electrophoretic mobility rapidly reaches a limiting value. Nevertheless, prolonged pre-exposure to enzyme leads to a continuing reduction in contact separations. This result taken with the observation that, for equal loss of electrophoretic mobility, a shorter contact separation results from pronase rather than neuraminidase pre-treatment implies that a non-electrostatic consequence of pronase pre-treatment dominates membrane interaction in the experimental regimes examined here. The average lateral contact separation for different enzyme regimes lay in the range 3.3 pm to a limiting lower value of about 0.7 pm. There was a good correlation between the logarithm of a contact separation index (the approach of separation distance to its limiting value) against the logarithm of a derived index related to net attractive interaction for a wide range of experimental conditions. Treatments which increased attraction or decreased repulsion (e.g. increased dextrans concentration or enzyme pre-treatment) lead to shorter lateral contact separation. This result is qualitatively consistent with the predicted behaviour for the dominant wavelength arising from interfacial instability of a thin aqueous film between adjacent membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00205812
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  • 5
    Electronic Resource
    Electronic Resource
    Membrane-Membrane contact: Involvement of interfacial instability in the generation of discrete contacts (1989)
    Springer
    Bioscience reports 9 (1989), S. 675-691 
    Details
    ISSN: 1573-4935
    Keywords: membrane contact ; membrane instability ; interfacial instability ; cell adhesion ; cell agglutination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The classical approach to understanding the closeness of approach of two membranes has developed from consideration of the net effect of an attractive van der Waals force and a repulsive electrostatic force. The repulsive role of hydration forces and stereorepulsion glycocalyx forces have been recently recognized and an analysis of the effect of crosslinking molecules has been developed. Implicit in these approaches is the idea of an intercellular water layer of uniform thickness which narrows but retains a uniform thickness as the cells move towards an equilibrium separation distance. Most recently an attempt has been made to develop a physical chemical approach to contact which accommodates the widespread occurrence of localized spatially separated point contacts between interacting cells and membranes. It is based on ideas drawn from analysis of the conditions required to destabilize thin liquid films so that thickness fluctuations develop spontaneously and grow as interfacial instabilities to give spatially periodic contact. Examples of plasma membrane behaviour which are consistent with the interfacial instability approach are discussed and experiments involving polycation, polyethylene glycol, dextran and lectin adhesion and agglutination of erythrocytes are reviewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01114806
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  • 6
    Electronic Resource
    Electronic Resource
    The digestion ofSaccharomyces cerevisiae byAcanthamoeba castellanii (1979)
    Springer
    Protoplasma 98 (1979), S. 63-71 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The digestion ofSaccharomyces cerevisiae byAcanthamoeba castellanii, at different times after feeding, has been examined by cytochemical techniques at electron microscope level and by measurement of yeast viability. The measurement of viability, combined with cytochemistry is presented as a novel method of examining the progress of digestion. Particular attention has been given to the temporal development of digestion. Vacuoles, probably primary lysosomes, have been identified containing acid phosphatase activity within minutes of feeding and these accumulate around and fuse with phagocytic vacuoles. Acid phosphatase levels in the digestive vacuoles appeared highest at 20 to 40 minutes. Yeast digestion was observed and yeast viability began to decline at this time. Mixing of autophagic and heterophagic material was also observed. At least half of the yeast population was still viable after 90 minutes. Our method (p-nitrophenyl phosphate) of enzyme localization has demonstrated plasma membrane associated acid phosphatase activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01676662
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  • 7
    Electronic Resource
    Electronic Resource
    Intrinsic electric fields and membrane bending (1984)
    Springer
    Journal of biological physics 12 (1984), S. 44-51 
    Details
    ISSN: 1573-0689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The fragmentation of human erythrocytes heated in a range of ionic environments has been examined by video microscopy, $$W$$ , the average number of surface wave crests growing on the cell rim during fragmentation by membrane externalization, andI, the percentage of cells internalizing membrane, were scored. The membrane diffusion potential was altered experimentally on decreasing the extracellular chloride concentration by substituting either membrane-impermeant sorbitol or Na gluconate for some NaCl. The external-membrane-face surface potential was altered either by surface charge depletion or by ionic strength changes. The dependence of morphological change on diffusion potential at constant cell volume and surface potentials was established over a 34-mV change in diffusion potential. The rate constants for morphological change with charge depletion at different diffusion potentials are largely independent of the diffusion potential. A l.O-mV increase in diffusion potential has an effect on morphological change of comparable magnitude to that of a 1.0-mV decrease in the modulus of the negative surface potential. When the diffusion potential increased on decreasing both the extracellular diffusible ion concentration and extracellular ionic strength, the effect on cell morphology of increasing the modulus of the surface potential was overcome by the effects of the diffusion potential change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01858252
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  • 8
    Electronic Resource
    Electronic Resource
    Divalent cation effects on membrane bending in heated erythrocytes (1984)
    Springer
    Journal of biological physics 12 (1984), S. 85-92 
    Details
    ISSN: 1573-0689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The thermal fragmentation of human erythrocytes involves either surface wave growth and membrane externalization at the cell rim or membrane internalization at the cell dimple. In symmetrical monovalent electrolytes an increase in membrane internalization at the cell dimple correlates with the decrease in zeta potential arising from surface charge (sialic acid residue) depletion. The influence of divalent cations on thermal fragmentation is examined in this work. The erythrocyte zeta potential decreased when divalent cations replaced some Na+ in the cell-suspending phase. The incidence of membrane internalization increased in rank order Ca2+〉Ba2+〉Mg2+≥Sr2+. Calcium continued to influence the thermal fragmentation of cells highly depleted of sialic acid, suggesting that the ion also interacted with membrane sites other than sialic acid. The divalent cation influence on cell fragmentation was shown to be greater than that due to zeta potential decrease alone. This conclusion was supported by the observation that the divalent cation-induced changes in zeta potential showed much less cation specificity than did the changes induced in the thermal fragmentation pattern. The result implies that the specificity of the divalent cation effects was due to interactions within the erythrocyte shear layer. The possibility that the interaction is with membrane lipids is examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870558
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetics of protein release from yeast sonicated in batch and flow systems at 20 kHz (1972)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 14 (1972), S. 33-42 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The release constant, k, of brewers yeast sonicated at powers up to 200 W at 20 kHz has been shown to be independent of cell concentration up to values of 60 g made up to 100 ml. It is inversely proportional to the volume of the treatment vessel in the range 75 to 450 ml, and almost proportional to the input acoustic power from 60 to 195 acoustic watts. A flow system is described and a relationship linking protein release, flow rate, and the protein release constant, determined from batch experiments, is derived. Good agreement between the theoretical prediction of protein release and experimental results with the flow system was obtained.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260140105
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  • 10
    Electronic Resource
    Electronic Resource
    Optimization of the release of undegraded material extracted from cells by ultrasound (1974)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 16 (1974), S. 659-673 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The time course of release of intact labile material from cells by cavitating ultrasound is examined. Curves are presented which show the yield of intact subcellular components obtainable from cells as a function of sonication time for various values of the ratio of inactivation rate to release rate. The general cases where inactivation of released product is concentration dependent (chemical) and concentration independent (mechanical) are considered.For a flow system the time of attainment of equilibrium concentration of active product is analyzed as a function of flow rate, release rate, inactivation rate, and volume of chamber. Curves of optimal yields to be expected for batch and flow systems are presented. It is shown that sonochemical inactivation can be made negligible by sonication of high cell concentration suspensions.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260160508
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