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  • cell culture  (37)
  • 36.40. +d  (35)
  • Springer  (72)
  • American Institute of Physics (AIP)
  • Cell Press
  • 1990-1994  (72)
  • 1991  (72)
Collection
Keywords
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  • Springer  (72)
  • American Institute of Physics (AIP)
  • Cell Press
  • Wiley-Blackwell  (7)
Years
  • 1990-1994  (72)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Toxicity of the mycotoxins fumonisins B1 and B2 and Alternaria alternata f. sp. lycopersici toxin (AAL) in cultured mammalian cells (1991)
    Springer
    Mycopathologia 116 (1991), S. 97-104 
    Details
    ISSN: 1573-0832
    Keywords: Fumonisin B1 ; fumonisin B2 ; AAL toxin ; T-2 toxin ; mycotoxin ; Fusarium moniliforme ; bioassay ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Fumonisins B1 and B2 and AAL toxin are a series of structurally related mycotoxins. Fumonisins B1 and B2, produced by Fusarium moniliforme Sheldon induce toxic hepatitis and hepatomas in rats and leukoencephalomalacia in horses. The cancer-promotion assay which has been used to guide their purification is slow and consumes large amounts of sample. We have examined a series of cultured mammalian cell lines in order to develop a more rapid and sensitive bioassay system, which may be useful for examining structure-activity relationships and the mechanism(s) of action of these toxins. Of 9 rat hepatoma cell lines tested, all except the two most de-differentiated lines were sensitive to the three toxins, with a toxic response visible by 48 h. Approximate IC50 values for the most sensitive hepatoma line, H4TG, were 4, 2 and 10 μg/ml for fumonisins B1, B2 and AAL toxin, respectively „in 100 μl cultures. Among 15 cell lines from other sources, only MDCK dog kidney epithelial cells were sensitive (IC50 = 2.5, 2 and 5 μg/ml, respectively). Studies in co-cultures of sensitive and insensitive cell lines and in cultures of a sensitive cell line over a range of cell densities indicated that cytotoxicity of fumonisins B1 and B2 does not involve metabolite activation to a derivative stable enough to diffuse to adjacent cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00436371
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  • 2
    Electronic Resource
    Electronic Resource
    Modified culture method for human corneal epithelial cells (1991)
    Springer
    Methods in cell science 13 (1991), S. 45-48 
    Details
    ISSN: 1573-0603
    Keywords: cell culture ; corneal epithelium ; primary explant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An improved procedure for the primary culture of pure human corneal epithelial cells from corneal explants is described. Confluent monolayers of epithelial cells can be consistently produced from small segments of donor corneas regardless of donor age and without feeder layers. Incubating segments on collagen at the air-liquid interface significantly improves the yield of cells per cornea and shortens cell migration time as compared to culturing on plastic. Fibroblast contamination is eliminated by serum-free medium and confirmed by indirect immunofluorescent staining for keratin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02388203
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  • 3
    Electronic Resource
    Electronic Resource
    Culture of human renal cortex epithelial cells (1991)
    Springer
    Methods in cell science 13 (1991), S. 143-147 
    Details
    ISSN: 1573-0603
    Keywords: kidney ; renal cortex ; proximal tubule ; enzymatic dissociation ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A procedure is described for the establishment and propagation of epithelial cell rich cultures derived from normal human kidney cortex (NHK-C cells). Cells are harvested from tissue fragments of donor human kidney by progressive enzymatic dissociation. NHK-C cultures are morphologically heterogeneous but exhibit, predominantly, the functional characteristics of cells of the kidney proximal tubule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02388118
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of low nitrate and high sugar concentrations on anthocyanin content and composition of grape (Vitis vinifera L.) cell suspension (1991)
    Springer
    Plant cell reports 9 (1991), S. 500-504 
    Details
    ISSN: 1432-203X
    Keywords: anthocyanin ; cell culture ; nitrate ; sucrose ; Vitis vinifera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In pigmented cells of Vitis vinifera suspension cultures, best accumulation of anthocyanins was obtained when nitrate concentration was reduced from 25 mM to 6.25 mM and when sucrose concentration was increased from 88 mM to 132 mM. Under such conditions growth was greatly decreased. However, cell viability was maintained. The increases in anthocyanins in pigmented cells were due largely to increases in peonidin — glucoside. The high sucrose and the low nitrate concentrations can be one of the important culture factors in controlling of anthocyanin production by cell cultures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232105
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  • 5
    Electronic Resource
    Electronic Resource
    A mechanism for the loss of cytochrome P-450 in primary mouse hepatocytes (1991)
    Springer
    Molecular and cellular biochemistry 108 (1991), S. 151-156 
    Details
    ISSN: 1573-4919
    Keywords: cytochrome P-450 ; mitochondria ; heme ; hepatocytes ; mitochondrial DNA ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract This study examined various biochemical parameters such as mitochondria and mitochondrial DNA (mtDNA), total heme and cyto P450 content in fresh hepatocytes and dedifferentiated hepatocytes. These parameters were chosen in order to understand the dramatic decrease in drug metabolism in cultured hepatocytes. The data in this study shows a temporal decrease in cytochrome P450, total heme and also a decrease in mitochondria. Also, the ratio of mtDNA content to mitochondrial density was found to increase as hepatocytes underwent dedifferentiation. Stereological analysis of cell preparations provided a measure of mitochondrial density per cell area and mtDNA content was assessed by the use of a specific radiolabelled probe. This study demonstrates that a loss of the organelle which is partially responsible for synthesis of heme correlates with a decrease in cytochrome P450.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00233120
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  • 6
    Electronic Resource
    Electronic Resource
    Adrenergic hormones and control of cardiac myocyte growth (1991)
    Springer
    Molecular and cellular biochemistry 104 (1991), S. 35-43 
    Details
    ISSN: 1573-4919
    Keywords: α1-adrenergic receptors ; β-adrenergic receptors ; cardiac muscle ; cell culture ; gene expression ; protein kinase C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The molecular mechanisms of cardiac myocyte growth are relevant to important problems in cardiovascular disease. A cell culture model has been developed to explore the role of adrenergic hormones in cardiac myocyte growth and gene expression. Activation of a cardiac myocyte α1-adrenergic receptor by catecholamines induces hypertrophic growth of neonatal rat cardiac myocytes and initiates selective increases in contractile protein gene transcription. These effects on growth and gene expression do not depend on contractile activity. The cardiac myocytes contain at least two subtypes of α1-adrenergic receptors and at least three isoforms of protein kinase C (PKC). A distinct α1 receptor subtype may mediate hypertrophy and gene transcription. Different isoforms of PKC are translocated to different intracellular sites on activation, and there is evidence that the β-PKC isoform may be an element in the signal transduction pathway from an α1 receptor at the surface to the cardiac myocyte nucleus. Growth regulation through a β-adrenergic receptor can also be demonstrated in the culture model. The growth response mediated through a β-adrenergic receptor differs in several respects from that transduced through an al adrenergic receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229801
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  • 7
    Electronic Resource
    Electronic Resource
    Sequence analysis of a chalcone isomerase cDNA of Phaseolus vulgaris L. (1991)
    Springer
    Plant molecular biology 16 (1991), S. 167-169 
    Details
    ISSN: 1573-5028
    Keywords: Phaseolus vulgaris ; cell culture ; chalcone isomerase ; elicitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00017927
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular cloning of a cDNA from Lupinus polyphyllus cell cultures encoding a ribosomal protein (rps16) (1991)
    Springer
    Plant molecular biology 16 (1991), S. 739-740 
    Details
    ISSN: 1573-5028
    Keywords: Lupinus polyphyllus ; cell culture ; cDNA clone ; ribosomal protein ; rps 16
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00023439
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  • 9
    Electronic Resource
    Electronic Resource
    Expression and stability of amplified genes encoding 5-enolpyruvylshikimate-3-phosphate synthase in glyphosate-tolerant tobacco cells (1991)
    Springer
    Plant molecular biology 17 (1991), S. 1127-1138 
    Details
    ISSN: 1573-5028
    Keywords: tobacco ; 5-enolpyruvylshikimate-3-phosphate synthase ; cDNA clone ; gene expression ; gene amplification ; glyphosate ; cell culture ; tolerance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two distinct cDNAs for 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) were obtained from a glyphosate-tolerant tobacco cell line. The cDNAs were 89% identical and the predicted sequences of the mature proteins were greater than 83% identical with EPSPS proteins from other plants. Tobacco EPSPS proteins were more similar to those from tomato and petunia than Arabidopsis. One cDNA clone, EPSPS-1, represented a gene that was amplified in glyphosate-tolerant cells, while the gene for EPSPS-2 was unaltered in these cells. Consequently, EPSPS-1 mRNA was more abundant in tolerant than unselected cells, whereas EPSPS-2 mRNA was at relatively constant levels in these cell lines. Exposure of unselected cells and tobacco leaves to glyphosate produced a transient increase in EPSPS mRNA. However, glyphosate-tolerant cells containing amplified copies of EPSPS genes did not show a similar response following exposure to glyphosate. A significant proportion of the EPSPS gene amplification was maintained when tolerant cells were grown in the absence of glyphosate for eight months. Plants regenerated from these cells also contained amplified EPSPS genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00028730
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  • 10
    Electronic Resource
    Electronic Resource
    Studies of serum-free medium for the generation of lymphokine-activated killer cells (1991)
    Springer
    Cytotechnology 6 (1991), S. 39-47 
    Details
    ISSN: 1573-0778
    Keywords: cell culture ; lymphocyte ; lymphokine-activated killer cell ; recombinant interleukin 2 ; serum-free medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We examined a serum-free medium (designated as TYI 101) for the generation of lymphokine-activated killer (LAK) cells from human lymphocytes, regional lymph node lymphocytes (RLNL) and peripheral blood lymphocytes (PBL). TYI 101 medium consisted of, in addition to nutrient mixture, transferrin, insulin, fetuin, sodium selenite, 2-mercaptoethanol, o-phosphorylethanolamine, chick egg yolk and porcine kidney extract. These hormones were effective for supporting RLNL proliferation as assessed by (3H)-thymidine uptake. When human lymphocytes from two different sources were cultivated with recombinant interleukin 2 (rIL-2) in TYI 101 medium, LAK activity was generated. In cultures of PBL from a healthy donor, LAK cells were generated in TYI 101 medium as efficiently as in RPMI 1640 medium supplemented with 10% human AB-type serum (RPMI-AB). In cultures of RLNL from lung cancer patients, LAK activity obtained in TYI 101 medium was about sixty-five percent of that in RPMI-AB. However, the addition of a small amount of AB-type serum improved the generation of LAK activity, LAK cell expansion, and cell viability in TYI 101 medium. We conclude that TYI 101 medium can be used for the generation of LAK cells from human lymph node lymphocytes with supplementation of none or only a reduced amount of human serum.
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    URL: http://dx.doi.org/10.1007/BF00353701
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  • 11
    Electronic Resource
    Electronic Resource
    Development of a new culture system for human lymphokine-activated killer cells: Comparison with a conventional static culture method (1991)
    Springer
    Cytotechnology 7 (1991), S. 75-83 
    Details
    ISSN: 1573-0778
    Keywords: adoptive immunotherapy ; cell culture ; cell culture apparatus ; Interleukin-2 ; lymphokine-activated killer cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract We recently developed a new culture system based on dialysis perfusion (designated JCC-device) for the generation and expansion of human lymphokine-activated killer (LAK) cells (Murata et al., 1990). More recently we have scaled up the volume of the culture vessel of the JCC-device from 100 ml to 400 ml for clinical use. In the present study, using this new 400 ml JCC-device, we cultured human lymph node lymphocytes (LNL) obtained from 8 surgical patients with primary lung cancer, and investigated the cellular characteristics in comparison with a conventional batchwise culture system using tissue culture dishes. With the JCC-device, the cell density reached a maximum 2.7×107 cells/ml with greater than 90% viability by the appropriate exchange of perfusion medium and by making additions at the appropriate intervals for recombinant interleukin-2 (rIL-2). The expansion fold of LNL with the JCC-device, ranging 6.6- to 19.2-fold (mean 13.8-fold), was not significantly different from that in dish cultures. There was no marked difference in cell surface phenotypes between the two culture systems in 7 out of 8 cases. As for LAK activity of LNL, the JCC culture was either superior or equal in 4 out of 8 cases, but inferior in the other 4 cases to the conventional dish cultures. In the latter cases, the usage of serum for the JCC culture was limited, which might have resulted in the low LAK activity. The JCC-device was able to reduce the consumption of basal medium, rIL-2 and serum by 20%, 84% and 96%, respectively compared to the conventional tissue culture systems. The JCC-device improved the routine performance of adoptive immunotherapy with LAK cells and rIL-2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350913
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  • 12
    Electronic Resource
    Electronic Resource
    A new method for the encapsulation of mammalian cells (1991)
    Springer
    Cytotechnology 7 (1991), S. 121-130 
    Details
    ISSN: 1573-0778
    Keywords: cell culture ; cellulose sulphate ; encapsulation ; monoclonal antibodies ; poly-dimethyl-diallyl-ammoniumchloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A new encapsulation method was developed for the cultivation of mammalian cells. The capsules were produced using a solution of sodium cellulose sulphate (CS)(1.5%) and poly-dimethyl-diallyl-ammoniumchloride (PDMDAAC). When CS droplets fell into the precipitation bath consisting of a 2% solution of PDMDAAC, immediately a membrane at the interphase was built up. The influences of varying encapsulation process parameters on capsule characteristics, cell growth, and monoclonal antibody production were tested. This new method showed advantages when compared to other methods mainly due to time simplicity of the whole process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350918
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  • 13
    Electronic Resource
    Electronic Resource
    Serum-free culture of carcinoma cell lines (1991)
    Springer
    Cytotechnology 5 (1991), S. 31-46 
    Details
    ISSN: 1573-0778
    Keywords: serum-free ; cell culture ; carcinoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00365532
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  • 14
    Electronic Resource
    Electronic Resource
    Influence of temperature on the proliferative response of rainbow trout gonadal fibroblasts to cortisol and RU 486 (1991)
    Springer
    Fish physiology and biochemistry 9 (1991), S. 261-269 
    Details
    ISSN: 1573-5168
    Keywords: Cortisol ; RU 486 ; temperature ; rainbow trout ; cell culture ; [3H]-Thymidine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The rainbow trout gonadal cell line, RTG-2, which survives temperatures from 0 to 28°C and proliferates at 5 to 26°C, responded to cortisol from 28°C to 0°C by influencing [3H]-thymidine incorporation into DNA. Over the normal temperature range of rainbow trout, 10–22°C, cortisol inhibited [3H]-thymidine incorporation. The antiglucocorticoid RU 486 had no effect on [3H]-thymidine incorporation at these temperatures and blocked the response to cortisol. Another antiglucocorticoid RU 362 also had no effect but was less effective in blocking the cortisol response. During incubation at 28°C this inhibitory response to cortisol was detected inconsistently during the first 24 h but was observed consistently during the second 24 h. At 0°C, cortisol and RU 486 had no effect during short treatments, but a 60 h exposure to either steroid stimulated [3H]-thymidine incorporation over a 48 h labelling period. These results suggest that temperature shifts between 10–22°C, do not change the direction of a response to cortisol and support the use of the upper portion (20–22°C) of the temperature range for studies on salmonid cells in culture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02265147
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  • 15
    Electronic Resource
    Electronic Resource
    Effects of high ammonium concentrations on growth and anthocyanin formation in grape (Vitis vinifera L.) cell suspension cultured in a production medium (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 169-174 
    Details
    ISSN: 1573-5044
    Keywords: ammonium ; anthocyanin ; cell culture ; growth kinetics ; production medium ; Vitis vinifera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cultivating Vitis vinifera cell suspensions in a production medium which is characterized by high sucrose and low nitrate concentrations (132 mM and 6.25 mM respectively) repressed growth but enhanced the intracellular accumulation of anthocyanins, especially peonidin 3-glucoside. Increasing the ammonium concentration of the production medium from 2 to 8–16 mM increased growth and decreased the accumulation of anthocyanins and peonidin 3-glucoside specifically. Instead, peonidin 3-p-coumaroylglucoside accumulated. At 24 mM ammonium concentration, growth was inhibited and accumulation of peonidin 3-p-coumaroylglucoside was significant (p〈0.05) and represented 42% of total anthocyanins after 12 days of culture compared with 19% in the production medium with 2 mM ammonium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00041286
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  • 16
    Electronic Resource
    Electronic Resource
    Ferric chelate reduction by suspension culture cells and roots of soybean: A kinetic comparison (1991)
    Springer
    Plant and soil 130 (1991), S. 75-80 
    Details
    ISSN: 1573-5036
    Keywords: cell culture ; FeHEDTA ; Glycine max ; iron chelate reduction ; iron nutrition ; soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The abilities of suspension cultures and intact roots of soybean (Glycine max L. cv. Hawkeye) to reduce ferric chelate were compared. Ferric chelate was supplied as ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) and reduction was measured spectrophotometrically using bathophenan-throlinedisulfonic acid (BPDS) as the ferrous scavenger. Ferric chelate reduction by cell suspension cultures showed typical saturation kinetics; however, no difference was observed between cells that had been continuously grown with Fe (+Fe) and those that had been grown for four days without added Fe (−Fe). Values for Km and Vmax, determined from a Lineweaver-Burk plot, were 57 μM and nmoles mg-1 dry weight for the +Fe cells and 50 μM and 22 nmoles mg-1 dry weight for the -Fe cells, respectively. Ferric chelate reduction by Fe-deficient roots also exhibited saturation kinetics, while roots grown with adequate Fe did not reduce ferric chelate. The Km and Vmax values for Fe-deficient roots were 45 μM and 20 nmoles mg-1 dry weight, respectively, and did not differ from values obtained for cells in culture. This study offers strong evidence that the mechanism responsible for the reduction of ferric chelate is the same for cultured cells and roots and that the process is controlled at the cellular level. We propose that suspension cultures can be used as an alternative to intact roots in the study of ferric chelate reduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00011858
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  • 17
    Electronic Resource
    Electronic Resource
    Actual, potential and speculative applications of seaweed cellular biotechnology: some specific comments on Gelidium (1991)
    Springer
    Hydrobiologia 221 (1991), S. 181-194 
    Details
    ISSN: 1573-5117
    Keywords: callus ; cell culture ; domestication ; protoplast ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cellular biotechnology is a promising application in the propagation and selection of superior strains of seaweeds. Although axenic cultures, organogenetic tissue cultures, vegetative micro-propagation, callus induction and high yields of agar from calli have been described for several species of Gelidium, a number of basic problems remain to be solved. These include standardized methods for obtaining axenic cultures, identification of requirements for organic nutrients, PGR's, cellular disorganization and reorganization, somaclonal variation and somatic incompatibilities. Future progress in seaweed biotechnology will depend on the resolution of many of these problems.
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    URL: http://dx.doi.org/10.1007/BF00028374
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  • 18
    Electronic Resource
    Electronic Resource
    Experiments with culture media for planarian cells (1991)
    Springer
    Hydrobiologia 227 (1991), S. 187-192 
    Details
    ISSN: 1573-5117
    Keywords: Turbellaria ; planaria ; cell culture ; leucine uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have tested various conditions for the culture of cells dispersed from planarians. The cells were procurred by digestion of planarian tissue in pronase and filtering through a nylon mesh. Using incorporation of L-[3H]leucine into protein as a gauge of cell growth, we found that the optimum salt concentration was about 50% of that for mammalian cells (about 160 mOsm) and that optimum pH was about 8. Sera from several species and a tetrapeptide (Arg-Gly-Asp-Ser, the cell-attachment sequence in fibronectin) greatly increased leucine uptake and extended cell survival up to a period of about two weeks. Various growth factors and some other substances tested had no effect on uptake of leucine, cell morphology, or survival. A few other compounds tested were cytotoxic. None of the experimental media promoted cell proliferation.
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    URL: http://dx.doi.org/10.1007/BF00027601
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  • 19
    Electronic Resource
    Electronic Resource
    Study of a factor produced by suspension-cultured Pinus radiata cells which enhances cell growth at low inoculum densities (1991)
    Springer
    Plant cell, tissue and organ culture 26 (1991), S. 53-59 
    Details
    ISSN: 1573-5044
    Keywords: cell culture ; cell wall ; conditioned medium ; inoculum density ; low inoculum growth factor ; Pinus radiata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pinus radiata cells in suspension culture abruptly lose their growth capacity when diluted below a critical inoculum density. This threshold density can be lowered by adding the supernatant (conditioned medium) from healthy cultures which have been grown separately at high densities. Fresh medium is conditioned rapidly indicating that the factor responsible is either potent or produced rapidly. Activity-response curves increase progressively with concentration indicating that still greater effect may be obtained if the factor can be concentrated following separation from other medium components. The effect is not mimicked by a number of candidate compounds (including auxins, cytokinins, polyamines and vitamins). Partial characterisation studies indicate that the factor is relatively small (〈1 000 dalton) and possibly an oligosaccharide. It is considered that the factor is an essential structural component of the walls of expanding cells where it is reversibly-bound.
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    URL: http://dx.doi.org/10.1007/BF00116610
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  • 20
    Electronic Resource
    Electronic Resource
    Two types of asymmetric acetylcholinesterase in chick hindlimb muscle: Developmental profiles,in Vivo and in cell culture, and recovery after inactivation (1991)
    Springer
    Cellular and molecular neurobiology 11 (1991), S. 191-201 
    Details
    ISSN: 1573-6830
    Keywords: acetylcholinesterase ; asymmetric-form types ; chick hindlimb muscle ; development ; cell culture ; diisopropylfluorophosphate inactivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. We have analyzed the behavior of two types of asymmetric molecular forms (A forms) of acetylcholinesterase (AChE) during development of chick hindlimb muscle,in vivo and in cell culture, and upon irreversible inactivation of peroneal muscle AChE with diisopropylfluorophosphate (DFP)in vivo. 2. In agreement with previous developmental studies on chick muscle, globular forms of AChE (G forms) are predominant in chick hindlimb at early embryonic ages, being gradually replaced by A forms as hatching (and, therefore, onset of locomotion) approaches. Of the two A-form types, AI appears and accumulates significantly earlier than AII, so that A/G and II/I ratios higher than 1 are attained only at about hatching time. 3. Cultures prepared from 11-day chick embryo hindlimb myoblasts express both types of A forms, with a combined activity of 27% of total AChE after 12 days in culture. AI forms appear again earlier and are much more abundant than type II asymmetric species through the life span of cultures. 4. All AChE activity in the peroneal muscle is irreversibly inactivated by injection of DFPin vivo. The recovery of A forms follows the same sequence described for normal development, with a delayed and slower recovery of AII forms as compared with AI. 5. Several hypotheses involving tail polypeptides or tissue target molecules, or posttranslational interconversion, are proposed to help explain the earlier appearance and accumulation of AI forms in chick muscle.
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    URL: http://dx.doi.org/10.1007/BF00712809
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  • 21
    Electronic Resource
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    Accumulation of peonidin 3-glucoside enhanced by osmotic stress in grape (Vitis vinifera L.) cell suspension (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 49-54 
    Details
    ISSN: 1573-5044
    Keywords: anthocyanin ; cell culture ; osmotic potential ; reverse-phase HPLC ; Vitis vinifera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cell cultures of grapes, Vitis vinifera L. cv Gamay Fréaux were grown under different conditions of external osmotic potential induced by an increase of sucrose concentration or by the addition of mannitol to the culture medium. Addition of 82 mM mannitol or increasing sucrose concentration to 132 mM had similar effects on repressing growth. Cyanidin 3-glucoside, peonidin 3-glucoside and peonidin 3-p-coumaroylglucoside are three main anthocyanins of Vitis cells. Increasing osmotic potential from −0.43 MPa to −0.8 MPa in the medium resulted in a significant intracellular accumulation of anthocyanin especially peonidin 3-glucoside in the pigmented cells. High osmotic potential appears to stimulate the methylation of anthocyanins. Osmotic potential is an important culture factor and may be useful in the controlling of anthocyanin production and composition.
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    URL: http://dx.doi.org/10.1007/BF00044265
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  • 22
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    Increased anthraquinone production in Galium vernum cell cultures induced by polymeric adsorbents (1991)
    Springer
    Plant cell, tissue and organ culture 24 (1991), S. 207-210 
    Details
    ISSN: 1573-5044
    Keywords: anthraquinone production ; cell culture ; Galium vernum ; polymeric adsorbents ; secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Anthraquinones produced by suspension cultures of Galium vernum are completely retained intracellularly. Surprisingly, in the presence of some polymeric adsorbents anthraquinones are partially released into the culture medium. The secretion and in situ removal stimulates anthraquinone production in cell cultures of Galium vernum. Best results were obtained with Wofatit ES and Amberlite XAD-2.
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    Isolation and characterization of Daucus carota L. cell lines resistant to 2-deoxy-D-glucose (1991)
    Springer
    Plant cell, tissue and organ culture 25 (1991), S. 147-152 
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    ISSN: 1573-5044
    Keywords: cell culture ; Daucus carota ; 2-deoxy-D-glucose ; invertase ; selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Variant carrot (Daucus carota L.) cell lines resistant to the growth inhibitory effects of the glucose analogue 2-deoxy-D-glucose (dGlc) were isolated utilizing a feeder plate technique. Growth of sensitive cells was less than 7.5% of controls on medium supplemented with 3.0 mM dGlc, whereas resistant variants achieved growth ranging from 15% to 70% of that in controls. Increased levels of acid invertase activity in variant cell lines in response to dGlc in the culture medium, together with decreased sensitivity of the acid invertase enzyme (EC 3.2.1.26) to dGlc, is proposed as one of several potential mechanisms contributing to the observed dGlc resistance.
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    Morphologic identification of epithelial cell types of the human tracheo-bronchus in cell culture (1991)
    Springer
    Methods in cell science 13 (1991), S. 5-11 
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    ISSN: 1573-0603
    Keywords: bronchial epithelium ; cell culture ; intermediate filaments ; carbohydrate cytochemistry ; lectins ; peroxidase-labeled lectins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A protocol is presented for correlating the morphology of human bronchial epithelial cells after Papanicolaou staining with their periodic acid schiff (PAS)/AB-reactivity, intermediate filament type, and the pattern of staining with lectins having specific affinities for glycoconjugates:griffionia simplicifolia (GSA-IB4; terminal alpha-d-galactose),Dolichos biflorus (DBA,N-acetyl-d-galactosamine). The combination of these stains identified differentiation markers in morphologic studies of normal, transformed, and malignant bronchial epithelial cells in culture.
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    Use of the pH-sensitive dye BCECF to study pH regulation in cultured human kidney proximal tubule cells (1991)
    Springer
    Methods in cell science 13 (1991), S. 205-209 
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    ISSN: 1573-0603
    Keywords: pH ; NH 4 + ; BCECF ; human kidney ; proximal tubule ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This protocol describes the use of the pH-sensitive, intracellularly trapped dye 2′,7′-bis (2-carboxyethyl), 5 (and -6) carboxyfluorescein (BCECF), to characterize the pH regulating mechanisms in cultured human kidney proximal tubule cells. This is a reliable method for intracellular pH measurements and is applicable to single cells, cell suspensions, and confluent cultures.
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    A direct fluorimetric DNA assay on cell suspensions (1991)
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    Methods in cell science 13 (1991), S. 285-288 
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    ISSN: 1573-0603
    Keywords: DNA ; fluorimetry ; fibroblast ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An improved direct fluorimetric assay is described using bisbenzimidazol fluorescence at 356 nm excitation and 458 nm emission wavelengths. The turbidity of the medium was shown to have no effect on fluorescence under an absorbance of 0.2 at the excitation wavelength. The method was evaluated by comparisons with a colorimetric DNA assay and cell counting. The linearity of fluorescence was determined up to 15μg/ml of DNA. The method was very reproducible and sensitive to detect 10 ng/ml of DNA and may be used for cell suspensions containing around 5000 cells/ml or more.
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    Fetal bovine oviduct epithelial cell monolayers: Method of culture and identification (1991)
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    Methods in cell science 13 (1991), S. 289-294 
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    ISSN: 1573-0603
    Keywords: fetal bovine ; oviduct ; cell culture ; microscopy ; immunocytochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Bovine epithelial cell monolayers were obtained for culture from fetal oviduct after in situ trypsinization. Isolated ciliated and secretory cells obtained in high yield with good viability were suspended in B2-MENEZO'S medium supplemented with 7.5% fetal bovine serum FBS. The plated primary cultures reached confluency 2 days after initial seeding, producing a monolayer of cohesive polygonal cells with viability of 85 to 95%. Associated with this large epithelial cell population, ciliated cells as well as a few elongated spindle cells were observed. After the first subculture the ciliated cells disappeared and the epithelial cells in the monolayer grew more rapidly to confluence than adult-derived cultures. In addition, frozen-thawed oviduct epithelial cells also maintained a level of 75 to 85% viability during postthaw subculture. The epithelial cells maintained their secretory activity in culture as indicated by electron microscopy and immunocytochemistry. The cell culture monolayers contained keratin, a specific cytoskeletal component of epithelial cells. This culture system may offer benefits for in vitro culture of mammalian embryos.
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    A method for estimating oxygen availability of stationary plant cell cultures in liquid media (1991)
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    Plant cell, tissue and organ culture 26 (1991), S. 195-201 
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    ISSN: 1573-5044
    Keywords: Brassica napus ; cell culture ; diffusion ; liquid medium ; oxygen availability ; protoplast culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A method for estimating the oxygen availability in plant cell cultures grown in stationary liquid media (e.g. many protoplast cultures) was developed. The method is based on short-term measurements of respiration rate versus oxygen concentration on a sample of cells, suspended in liquid media. From such data it is possible to estimate the oxygen concentration at the bottom of a stagnant liquid culture, by calculating the amount of oxygen reaching the cells by diffusion. As an example, rape (Brassica napus L. cv. Omega) hypocotyl protoplasts were grown with different oxygen concentrations at the site of the cells, obtained by varying the cell density, the height of the liquid layer and the oxygen content of the gas phase. The number of surviving calli was positively correlated with the estimated oxygen availability in the range between 60 and 350 μM O2, below 60 μM all cells died. This indicates that oxygen availability can be a limiting factor in the range usually encountered in protoplast cultures, and that the method can be useful when designing optimal growth conditions for stationary cultures of plant cells.
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    l-Phenylalanine ammonia-lyase in suspension culture cells of spruce (Picea abies) (1991)
    Springer
    Plant cell, tissue and organ culture 27 (1991), S. 267-274 
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    ISSN: 1573-5044
    Keywords: cell culture ; enzyme induction ; fungal elicitor ; l-phenylalanine ammonia-lyase ; Picea abies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activity of l-phenylalanine ammonia-lyase (PAL) (EC 4.3.1.5) was determined in seedlings, callus cells, cell suspension cultures and in young needles of spruce (Picea abies) (L.) (Karst). PAL activity increased up to 10 fold in response to transferring suspension cultured cells into new cultivation medium. PAL was also induced about 10 fold when callus cells were transferrd into liquid medium. The increase was transient and it required the presence of a carbohydrate. In cell suspension cultures, grown in the dark (white cells), but not in light-grown cultures (green cells), PAL activity was induced up to 30 fold by UV-light. With a cell wall preparation of Rhizosphaera kalkhoffii, a forest pathogenic fungus, used as elicitor, the activity of PAL could be induced more than 10 fold. The degree of induction depended on the elicitor concentration. Induction was prevented by cycloheximide but not by actinomycin D.
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    Proteoglycan synthesis in cultures of murine retinal neurons and photoreceptors (1991)
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    Cellular and molecular neurobiology 11 (1991), S. 579-591 
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    ISSN: 1573-6830
    Keywords: proteoglycans ; glycosaminoglycans ; mouse retina ; photoreceptors ; retinal neurons ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. In recent years, a number of histochemical and immunocytochemical studies have suggested that proteoglycans, particularly those in the inter-photoreceptor matrix, exhibit altered distributions in several murine models for retinal degenerations. We are using a cell culture system to characterize the proteoglycans synthesized by neurons and photoreceptors derived from mouse retina, with the long-term goal of analyzing their role in retinal degenerations. 2. In this study we describe initial studies using cells derived from the retinas of normal mice. Cultures of retinal neurons and photoreceptors, which were free of glial, epithelia, or endothelial cells, were labeled with3H-glucosamine and35SO4. Proteoglycans isolated from the medium and cell layer were analyzed on the basis of charge, relative hydrodynamic size, and glycosaminoglycan content. 3. The studies indicate that the cultures actively synthesize proteoglycans. The medium contained predominantly chondroitin sulfate/dermatan sulfate, while the cell layer had a higher proportion of heparan sulfate, indicating a differential distribution between the two compartments.
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    Electronic shells and shells of atoms in metallic clusters (1991)
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    The European physical journal 19 (1991), S. 25-29 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 82.80Ms
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    Topics: Physics
    Notes: Abstract Intensity anomalies (magic numbers) have been observed in the mass spectra of sodium clusters containing up to 22 000 atoms. For small clusters (Na n ,n≤1500) the anomalies appear to be due to the filling of electronic shells (groups of subshells having the same energy). The shells can be characterized rather well by a pseudoquantum-number, indicating the possible existence of a symmetry higher than spherical. The mass spectra of larger clusters (1500≤n≤22 000) are well explained by the completion of icosahedral or cuboctahedral shells of atoms. The fact that the two types of shells (electron and atom) occur in distinct and non-overlapping size intervals might indicate the existence of a “liquid” to “solid” transition in going from small to large clusters.
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    Electronic structure of selenium- and tellurium-clusters (1991)
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    The European physical journal 19 (1991), S. 233-235 
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    ISSN: 1434-6079
    Keywords: 33.60.Cv ; 36.40. +d
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    Topics: Physics
    Notes: Abstract The vacuum-UV-photoelectron spectra (hν=10.0 eV or 8.3 eV) of selenium- and tellurium-clusters of different sizes (up to Se25 and Te8) were measured in a molecular beam by a photoion-photoelectron-coincidence experiment. Especially, the photoelectron spectra (4p-π-electrons) of the selenium-clusters converge with growing cluster size to the well known spectra of amorphous solid selenium by taking into account the dielectric constant of the bulk material. The experimental results indicate the first evidence that larger selenium aggregates are van der Waals clusters of the molecules Se5, Se6, Se7 and Se8 which are contained in the equilibrium vapour.
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    Comparison between selenium and tellurium clusters (1991)
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    The European physical journal 19 (1991), S. 237-239 
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    Keywords: 35.20.Vf ; 36.40. +d
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    Topics: Physics
    Notes: Abstract Selenium and tellurium clusters are produced by the inert gas condensation technique. The mass spectra of both species are completely different and reveal different properties. In selenium, a periodicity of 6–7 is observed and may be interpreted by the binding energy between small cyclic molecules. Moreover, it was very difficult to obtained large clusters probably because the binding energy between these molecules is very small. In tellurium, these periodic structures do not exist and large clusters are easily obtained in nucleation conditions where only small selenium clusters are present. These results are discussed and a simple nucleation model is used to illustrate this different behavior. Finally these clusters properties are correlated to the bulk structure of both materials.
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    Magnetic properties of free alkali and transition metal clusters (1991)
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    The European physical journal 19 (1991), S. 241-245 
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    ISSN: 1434-6079
    Keywords: 75.50.Bb ; 36.40. +d
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    Topics: Physics
    Notes: Abstract The Stern-Gerlach deflections of small alkali clusters (N〈6) and iron clusters (10〈N〈500) show that the paramagnetic alkali clusters always have a non-deflecting component, while the iron clusters always deflect in the high field direction. Both of these effects appear to be related to spin relaxation however in the case of alkali clusters it is shown that they are in fact caused by avoided level crossing in the Zeeman diagram. For alkali clusters the relatively weak couplings cause reduced magnetic moments where levels cross. For iron clusters however the total spin is strongly coupled to the molecular framework. Consequently this coupling is responsible for avoided level crossings which ultimately cause the total energy of the cluster to decrease with increasing magnetic field so that the iron clusters will deflect in one direction when introduced in an inhomogeneous magnetic field. Experiment and theory are discussed for both cases.
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    Metallic susceptibility in giant molecule: Pd561Phen36O200 (1991)
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    The European physical journal 19 (1991), S. 267-270 
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    ISSN: 1434-6079
    Keywords: 75.20.−g ; 35.20.My ; 36.40. +d
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    Topics: Physics
    Notes: Abstract The giant metal cluster molecule Pd561Phen36O x is the largest member of a series that has recently been prepared by Schmid [1]. Pronounced size effects are expected to show up in the magnetic properties of metal particles of the size of the Pd-561 core of the molecule. We have measured the susceptibility on four different batches of the material, with quite satisfactory reproducibility. There is a low temperature tail that is attributed to small amounts of impurities. The nearly temperature-independent paramagnetism that is observed is most probably due to an exchange enhanced Pauli spin susceptibility and is already close to the bulk value. The absence of size effects, i.e. a drop at low temperatures, is either due to interactions between the clusters or a result of a very small energy level spacing.
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    Electronic properties of divalent-metal clusters (1991)
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    The European physical journal 19 (1991), S. 165-167 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
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    Topics: Physics
    Notes: Abstract The transition from van der Waals to metallic bonding expected to occur in divalent-metal clusters (e.g., Be n , Mg n , Hg n ) as a function of cluster size is discussed. Theoretical results for several electronic properties reflecting this transition in Hg n -clusters are briefly reviewed and compared with available experiments. The limitations of the present theory particularly concerning the role of correlations and van der Waals interactions are discussed and possible improvements are suggested.
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    Semiclassical variational calculation of liquid-drop model coefficients for metal clusters (1991)
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    The European physical journal 19 (1991), S. 101-103 
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    Keywords: 36.40. +d ; 31.20.Lr ; 31.20.Sy ; 03.65.Sq
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    Topics: Physics
    Notes: Abstract We report on semiclassical density variational calculations for spherical alkali metal clusters in the jellium model. We derive liquid-drop model expansions for total energy, ionisation potential and electron affinity and test the coefficients numerically for clusters with up toN=105 atoms. From the limitN→∞, we obtain excellent agreement with surface tensions and work functions evaluated for an infinite plane metal surface.
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    Ultraviolet photoelectron studies of the molecules Se5, Se6, Se7 and Se8 with relevance to their geometrical structure (1991)
    Springer
    The European physical journal 19 (1991), S. 229-231 
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    ISSN: 1434-6079
    Keywords: 31.20. +Z ; 33.60.Cv ; 35.20.Vf ; 36.40. +d
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    Topics: Physics
    Notes: Abstract The vacuum-UV-photoelectron spectra (hν=10.0 eV) of Se2, Se5, Se6, Se7 and Se8 were measured. The isolated particles were examined in a supersonic molecular beam employing the photoelectron-photocation-coincidence technique. The structures of the photoelectron spectra of selenium molecules with even and odd numbers of atoms differ in a characteristic manner. Whereas the spectra of Se6 and Se8 show one single broad band, three separated bands with different intensities are observed for Se5 and two for Se7. An attempt to connect these experimental observations with the geometrical structure of the molecules shows that the photoelectron spectra are consistent with theC 1h -symmetry of the Se5 and Se7 rings proposed in the literature.
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    Simple metal clusters (1991)
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    The European physical journal 19 (1991), S. 1-6 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 35.20
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    Topics: Physics
    Notes: Abstract The response of alkali cluster ions to an optical excitation is investigated for two different photon energy domains. Below the ionization potential giant resonances in the photoabsorption cross-section are observed for closed shell species. Above the ionization potential, the ionization process competes with the photofragmentation process. The number of valence electrons determines both the behavior of the photoabsorption spectrum and the evolution of the ionization cross-section with the cluster size. The stability of the clusters against an excess of charge is examined through the observation of an asymmetric fission of Na n ++ . Experimental results are discussed in term of an electrostatic model giving an estimate of the critical size of stability and of the height of the coulombic barrier.
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    Optical spectra of sodium microclusters (1991)
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    The European physical journal 19 (1991), S. 43-45 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 33.20.Kf
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    Topics: Physics
    Notes: Abstract Photoabsorption spectra have been measured for free neutral sodium clusters containing fromN=3 to 40 atoms. In the size range ofN≈3 to 5, a transition occurs from molecule-like absorption to collective excitations of the valence electrons. ForN≈6 to 12, the data are well described by an ellipsoidal shell model. In open-shell clusters, the multiple surface plasma resonances expected for spheroidal or ellipsoidal shapes are observed. The experimental resonance positions provide a sensitive measurement of the cluster distortions. ForN≳13, the per atom strength of these collective resonances is reduced; this may be due to peak fragmentation caused by interaction between the surface plasmon and nearby single-electron resonances. In three distinct wavelength regions, one of which corresponds to the position of the Na atom “D-lines”, additional absorption is seen in the spectra of all investigated clusters.
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    Thermal electronic properties of alkali clusters (1991)
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    The European physical journal 19 (1991), S. 51-53 
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    Keywords: 36.40. +d ; 31.20.Sy ; 05.30.−d ; 65.60. +m
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    Topics: Physics
    Notes: Abstract We apply the finite-temperature Kohn-Sham method to alkali metal clusters, using the spherical jellium model and treating the valence electrons as a canonical system in the heat bath of the ions. We study the shell effects in the total free energyF(N) and the entropyS(N) for neutral clusters containingN atoms. Their strongest temperature dependence is due to the finite ground-state valueS 0〉0 of the electronic entropy for non-magic clusters. It leads to a decreasing amplitude and an increasing smear-out of the saw-tooth structure in the first difference Δ1 F(N)=F(N−1)−F(N) with increasing temperatureT and cluster sizeN.
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    Applying ZEKE-spectroscopy to clusters (1991)
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    The European physical journal 19 (1991), S. 59-61 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 33.60. −q
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    Topics: Physics
    Notes: Abstract In this paper we describe the application of a special form of electron photodetachment spectroscopy, zero electron kinetic energy (ZEKE) spectroscopy, to the study of cold metal cluster anions. From this study we have obtained vibrational and thus structural information of several neutral and charged clusters, e.g. Au 2 −/0 , Ag 3 −/0 , Sn 2 −/0 and Al 3 −/0 . In addition, in separate measurements of the relative photodetachment cross section of Au 2 − , we have discovered sharp resonances which are due to electronic autodetachment from a short lived excited state.
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    A pseudo-Jahn-Teller treatment of the B system of Na3 (1991)
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    The European physical journal 19 (1991), S. 63-66 
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    Keywords: 33.10 Lb ; 33.70. −w ; 36.40. +d
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    Topics: Physics
    Notes: Abstract TheB system of the two-photon ionization spectrum of Na3 often is quoted as an example of fractional quantization of the pseudorotational motion. In the present paper we investigate the influence of a nearby electronic state on the nuclear motion. It turns out that the experimental results may be understood equally well in a picture which implies integer instead of fractional quantization of the pseudorotation.
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    Photoabsorption spectra of Cs n O and Cs n clusters (1991)
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    The European physical journal 19 (1991), S. 81-84 
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    Keywords: 36.40. +d ; 33.20 Ea
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    Topics: Physics
    Notes: Abstract Photoabsorption spectra of several Cs N+2O and Cs N clusters were obtained by means of laser-induced beam-depletion techniques. The strong absorption of clusters withN≥3 in the near infrared indicates that collective motion might play an important role. Dipole transitions between molecular orbitals, enhanced by plasmon oscillations, generate remarkably distinct spectra for(a) closed-shell clusters atN=8 and(b) geometrically symmetric clusters like Cs6O and Cs14O.
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    The response of metal clusters toq- andL-dependent external fields (1991)
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    The European physical journal 19 (1991), S. 89-91 
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    Keywords: 36.40. +d ; 31.20.Sy ; 71.45.Gm
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    Topics: Physics
    Notes: Abstract We have calculated the static polarizability and mean excitation energy of metal clusters submitted toq-andL-dependent external fields ofj L (qr)Y L0(Ω) type. Use has been made of an Extended Random-Phase Approximation which includes exchange and correlation effects within a local model, and of the spherical jellium model to describe the neutralizing positive background.
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    Surface and volume collective modes in small clusters and their interaction with single-particle levels (1991)
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    The European physical journal 19 (1991), S. 105-107 
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    Keywords: 36.40. +d ; 72.45. −d ; 31.20.Lr
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    Topics: Physics
    Notes: Abstract As has been recently established, collective excitations in small metal clusters exhibit some unusual features. A theoretical analysis of cluster photoabsorption spectra is presented. It is shown that small systems can support volume collective modes which, unlike in the case of bulk metals, make a noticeable contribution to photoabsorption. Furthermore, single particle-hole transitions cause splitting of resonance peaks. The theory agrees well with experimental data.
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    The self-consistent spheroidal jellium model of open-shell monovalent metal clusters (1991)
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    The European physical journal 19 (1991), S. 109-111 
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    Keywords: 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recently, we have proposed a microscopic model, describing the properties of open-shell, Jahn-Teller deformed monovalent-metal clusters [1]. The model is based on the self-consistent ground-state calculation, allowing the spheroidal (axial) deformation of the ionic jellium background, driven by the open-shell valence electron structure. The ground state electronic properties of such clusters are further investigated and compared to recent experimental data: ionization potentials, electron affinities and binding energies of neutral monomers to cationic clusters [2].
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    Calculated electronic properties of medium sized sodium clusters: the inhomogeneous jellium model (1991)
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    The European physical journal 19 (1991), S. 113-115 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 31.20.Sy ; 71.25.M
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    Topics: Physics
    Notes: Abstract Recently observed magic number data for Na N clusters in the size range from 100 to 900 atoms cannot be fully explained by density functional calculations using a homogeneous, spherical positive charge background. However, a centrally compressed spherical background yields steps in the ionization potential at just those magic numbers observed experimentally.
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    Investigation of large electronic shells in Cs-compound clusters (1991)
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    The European physical journal 19 (1991), S. 117-119 
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    ISSN: 1434-6079
    Keywords: 71.50. +t ; 31.20.Sy ; 36.40. +d ; 82.80.Ms
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    Topics: Physics
    Notes: Abstract Magic numbers in cluster mass spectra can be caused by either geometric or electronic structure. The study of metallic compound clusters allows the number of atoms and the number of electrons in clusters to be controlled independently. We report magic numbers in the mass spectra of Cs-compound clusters containing up to 700 free electrons.
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    Multipotential model for atoms in alkali microclusters (1991)
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    The European physical journal 19 (1991), S. 121-124 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 21.60.Cs
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    Topics: Physics
    Notes: Abstract An alkali-atom shell model for alkali microclusters is introduced, where the quantum constituent is the neutral atom itself considered as a heavy fermion in a central potential created by all atoms in each shell of the cluster. Thus, here the magic numbers are due to atoms and not to electrons as in jellium models. The model is applicable under conditions (of production, temperature, size, etc.) not favoring delocalization of valence electrons. For conditions favoring electron delocalization the jellium model is applicable. New experiments are suggested via nuclear methods.
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    Small clusters made up of three kinds of neutral alkali atoms (1991)
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    The European physical journal 19 (1991), S. 125-127 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 21.80. +a
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    Topics: Physics
    Notes: Abstract Small clusters made up of three kinds of neutral alkali atoms, i.e. clusters of the form X ℓ Y m Z n , are theoretically studied. These clusters exhibit three series of magic numbers, one for each kind of atoms. That is,ℓ,m, andn independently can be magic numbers rather than their cumulative numberℓ+m+n or, in other words, magic numbers in alkali clusters composed of neutral atoms are due to atoms rather than to delocalized electrons as in jellium model. Of course, if conditions favor delocalization of electrons,ℓ+m+n can be magic but then we have no neutral atoms which are prerequisite for an application of the present model.
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    Electronic properties of aluminum clusters compared with the jellium model (1991)
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    The European physical journal 19 (1991), S. 133-135 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
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    Topics: Physics
    Notes: Abstract The experimental polarizabilities, ionization potentials and electron affinities of aluminum clusters are compared with jellium predictions. It is found that the clusters have radii and work functions which are close to the jellium model predictions for clusters with more than 13 atoms. The polarizabilities of Al n correspond with the jellium only forn〉40 and the shell structure features in the ionization potentials are anomalous up to 37. We conclude that nonjellium effects are important up ton=40.
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    Stability of isomeric Na n clusters (1991)
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    The European physical journal 19 (1991), S. 141-143 
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    Keywords: 31.20.Sy ; 36.40. +d
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    Topics: Physics
    Notes: Abstract A method which combines density functional theory and the use of pseudopotentials is applied to obtain ground state and low-lying metastable geometries of Na n clusters (7≤n≤40). The large variation in the magnitude of energy gaps between isomers suggests that the melting temperature is not a simple monotonous function of size. A detailed study of the differences between electronically stabilized (n=8, 20, 40) and structurally stabilized (n=13) clusters suggests some clues to understand the intriguing behaviour of Na13.
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    Shell effects on fragmentations of doubly-charged silver clusters (1991)
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    The European physical journal 19 (1991), S. 149-150 
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    Keywords: 36.40. +d
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    Topics: Physics
    Notes: Abstract Shell effects are found in the size distributions of fission fragments from doubly-charged silver clusters. The energy differences between parent cluster and sum of a pair of fragmented clusters are calculated for various fission channels using the theory of shell corrections. Oscillative structures observed in the size distribution are shown to be due to shell effects of fragments. It is also found that the cluster deformation due to shell effects produces the even-odd alternation in the size distribution.
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    Shell effects on symmetric fragmentations of alkali-metal clusters (1991)
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    The European physical journal 19 (1991), S. 145-147 
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    Keywords: 36.40. +d
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    Topics: Physics
    Notes: Abstract Symmetric fragmentation of multiply charged alkali-metal clusters consisting of several tens of atoms is studied. The energy variation during the fragmentation process is calculated using the theory ofshell corrections, in which total energy is written as a sum of the liquid-droplet and shell correction terms. It is found that the variation of the shell correction term is much larger than that of the liquid-droplet one if the parent cluster is metastable. Fragmentation into nearly-magic cluster is most favored regardless of parent size since the barrier height for fragmentation is mainly determined by the shell configuration of fragments rather than that of the parent.
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    Electronic shell structure in multiply charged silver clusters (1991)
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    The European physical journal 19 (1991), S. 151-152 
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    Keywords: 36.40. +d
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    Topics: Physics
    Notes: Abstract Silver clusters are generated by standard laser vaporization technique and ionized via multiphoton ionization. Time-of-flight mass spectrometry reveals singly, doubly and triply charged clusters, Ag n z+ (z=1,2,3). The spectra show, for all charge states, intensity variations, indicating enhanced stabilities for cluster sizes with closed electronic configurations in accord with the spherical jellium model.
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    Photoelectron spectroscopy and UV/Vis-photoabsorption spectroscopy of isolated clusters (1991)
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    The European physical journal 19 (1991), S. 161-164 
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    ISSN: 1434-6079
    Keywords: 33.60.Cv ; 35.20.Vf ; 36.40. +d
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    Topics: Physics
    Notes: Abstract Experimental innovations have allowed for the application of rather conventional spectroscopic molecular beam techniques to the study of electronic properties of molecular beam isolated neutral aggregates. Recent results for mercury clusters obtained by photoelectron spectroscopy and photoabsorption spectroscopy will be discussed. The experimentally available data for mercury clusters indicate a size dependent gradual evolution of metallic bulk properties in the approximate size region between 13 and 70 atoms.
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    Optical spectroscopy on size selected gold clusters deposited in rare gas matrices (1991)
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    The European physical journal 19 (1991), S. 157-159 
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    ISSN: 1434-6079
    Keywords: 29.25.Cy ; 36.40. +d ; 78.40. −q
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    Topics: Physics
    Notes: Abstract We report on the successful “soft-landing” of size selected Au trimers in solid Krypton matrices. The Au cations are produced by sputtering, mass-selected in a quadrupole mass spectrometer, co-deposited with Krypton on a cooled CaF2 substrate, and neutralized by low energy electrons. The deposition of low kinetic energy cations (10 eV) gives rise to strong excitation bands, detected by the emitted fluorescence light, which are unambiguously attributed to Au trimers. The deposition and fragmentation process is qualitatively discussed.
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    Bonding properties of IIA and IIB dimers in density functional theory with gradient corrections to the local density approximation (1991)
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    The European physical journal 19 (1991), S. 169-171 
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    ISSN: 1434-6079
    Keywords: 31.20. −d ; 31.20.Sy ; 36.40. +d
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    Topics: Physics
    Notes: Abstract We have computed bonding properties of the IIA and IIB homonuclear dimers within the Pseudopotential — Density Functional scheme, including Gradient Corrections to the Local Density Approximation (LDA). Our computations confirm that Gradient Corrections offer a significant improvement over LDA for what concerns ground state properties of finite systems: The LDA error on bond energies is reduced by more than 50%. Although less impressive, the relative improvement on equilibrium distances and vibrational frequencies is also systematic and important. We briefly discuss the relevance of our results to the description of the non-metal to metal transition expected in clusters of these elements as a function of size.
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    Structural and dynamical properties of magnesium microclusters (1991)
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    The European physical journal 19 (1991), S. 173-176 
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    Keywords: 36.40. +d ; 31.20.Sy ; 61.50.Cj
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    Topics: Physics
    Notes: Abstract We present systematic Density Functional Theory-Local Density Approximation computations for neutral Magnesium clusters Mg n withn≤13. For the smaller sizes the ground state structure is optimized starting from selected symmetries and allowing for relaxation, Jahn-Teller distorsion and spin polarization. For the larger sizes we perform a simulated annealing based on the ab-initio Molecular Dynamics. By the same method, we study the thermal and dynamical properties of Mg10 and Mg16. The general picture emerging from these computations shows that already atn ≈10 these clusters have acquired many characteristic features of metallic Magnesium.
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    Structure of small rare earth clusters (1991)
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    The European physical journal 19 (1991), S. 191-193 
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    Keywords: 35.20.Vf ; 36.40. +d
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    Topics: Physics
    Notes: Abstract Rare earth clusters are produced by the inert gas condensation technique. The observed size distribution shows large peaks atn=13, 19, 23, 26, 29, 32, 34, 37, 39, 45, ... The beginning of this sequence (up to 34) has been already observed in argon clusters and recently by our group in barium clusters; this sequence may be interpreted in terms of icosahedral structures corresponding to the addition of caps on a core icosahedron of 13 atoms.
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    Generation of rare earth metal clusters by means of the gas-aggregation technique (1991)
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    The European physical journal 19 (1991), S. 195-197 
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    Keywords: 36.40. +d ; 35.20 Wg
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    Topics: Physics
    Notes: Abstract Generation of rare-earth clusters is achieved using a gas aggregation technique. Varying the nucleation conditions induces a change in the relative cluster abundances. This can be understood in terms of competing cubic versus icosahedron structures.
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    Photoabsorption spectra ofs 1-electron metal clusters (1991)
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    The European physical journal 19 (1991), S. 13-17 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 33.80.Gj ; 33.20Kf
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    Topics: Physics
    Notes: Abstract Collinear laser/molecular beam photodepletion spectroscopy has developed into a powerful tool for the determination of electronic absorption in neutral alkali metal clusters free of perturbing matrix effects. We briefly discuss the method, present data on selected Na x and Li y Na x−y ,x≤20, contrast measurements with the known optical response of larger colloidal metal clusters, compare microcluster spectra with the predictions of various models and speculate on future experimental and theoretical developments in this field.
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    Silver-halogen cluster compounds Ag n X m (n≥2; 0≤m≤n;X=F, Br) (1991)
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    The European physical journal 19 (1991), S. 401-404 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
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    Topics: Physics
    Notes: Abstract Nonstoichiometric silver-halogen cluster compounds Ag n X m (0≤m≤n;X=F, Br) are generated by cocondensation of Ag atoms and AgX species using a slightly modified gas aggregation technique. The AgX molecules are produced by partial decomposition of SF6 and Br2 respectively at the surface of the hot silver containing crucible, followed by the reaction of halogen atoms with silver, giving rise to the formation of AgX molecules. In a heterogeneous nucleation between these molecules and evaporated Ag atoms the afore mentioned cluster compounds are formed. The degree of halogenation can either be controlled by the adjustment of the silver evaporation rate, or even more easily by controlling the partial pressure of the halogenating agent. The mass spectra of singly charged halogenated clusters, which are generated by electron impact ionization, reflect the stability of ions. These mass spectra demonstrate that there is an alternation in the intensity pattern up to a relatively high degree of halogenation (m) for each of the investigated compound series Ag n X m ,n≤8. This behavior is similar to the well-known odd-even effect for pure metal clusters, allowing us to postulate the existence of a “metallic” core which governs the stability of the cluster ion (at least for not too high degree of halogenation).
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    Size effect in3He n aggregates. A Gutzwiller approach (1991)
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    The European physical journal 20 (1991), S. 273-276 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 31.20.Tz ; 67.50. -b
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    Topics: Physics
    Notes: Abstract The Hubbard hamiltonian (where only intraatomic correlations between fermions are taken into account) is particularly well suited for the description of3He systems. It has already been used in the description of point defects (such as spin polarons) in the bulk. The variational Gutzwiller method is one of the most useful way for treating the Hubbard hamiltonian. This technique has been applied with success by Vollhardt to the bulk. We apply it here to aggregates. Our main results are the following: 1 existence of a critical size,N c , above which3He n begin to be stable; 2 calculation of the magnetic susceptibility. In this part two cases are studied: low magnetic field where only the density of states, σ(E F), at the Fermi level is needed and high magnetic field where the whole density of states is needed. The results are compared with other theoretical calculations.
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    Nutrient optimization for high density biological production applications (1991)
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    Cytotechnology 5 (1991), S. 15-30 
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    ISSN: 1573-0778
    Keywords: high density ; cell culture ; serum-free medium ; hybridoma ; CHO cells ; virus production ; insect cells ; adoptive immunotherapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Conclusion At the 1989 annual meeting of the U.S. Tissue Culture Associations, Ricahrd am, a leading investigator in the serum-free nutrient requirements of cultured cells, commented on the process of medium development. He noted that a survey of major media manufacturers revealed that, among the top selling mammalian cell culture media formulations, most were nearly thirty years old. This commentary is noteworthy considering the tremendous changes in cell culture understanding and derived applications which have emerged over these three decades. Fastidious cell types relatively unknown to investigators of the 1950s and 1960s are now being cultivated in defined, serum-free environments. Culture environments range from limiting dilution clonal recoveries to maintenance cultures approaching tissue densities. While research applications continue to predominate, applications of cell culture have expanded to the engineered production of biopharmaceuticals, to replacement of animal models for toxicology testing, and to the preservation, activation and expansion of human cells, tissues and organs. It is likely that future nutrient medium development will be predicated upon the design of a minimal number of defined formulations of relatively generic utility to a broad class of cell types. Analytical techniques derived from those described herein will be exploited in the user laboratory and in collaboration with the supplier to optimize the nutrient composition for the desired biological response.
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    Growth and protein production kinetics of a murine myeloma cell line transfected with the human growth hormone gene (1991)
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    Cytotechnology 5 (1991), S. 223-231 
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    ISSN: 1573-0778
    Keywords: cell culture ; kinetics ; Ig promoter/enhancer ; plasmacytoma ; recombinant protein production
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    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A model mammalian cell system for the production of recombinant proteins was investigated. Murine myeloma cells which had lost the ability to produce both heavy and light chain immunoglobulin molecules were transfected with a vector containing the immunoglobulin heavy chain promoter and enhancer elements linked to the human growth hormone gene. The growth kinetics of G32, a clonal isolate, were found to be similar to both the parent myeloma and hybridomas. However, production of hGH by G32 was growth associated, rather than as a secondary metabolite as is the case for hybridomas. In addition, G32 produced hGH at molar levels greater than most hybridomas.
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    Primary cell culture from embryos of the Japanese scallop Mizuchopecten yessoensis (Bivalvia) (1991)
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    Cytotechnology 6 (1991), S. 49-54 
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    ISSN: 1573-0778
    Keywords: Bivalvia ; cell culture ; embryo ; mitosis ; scallop
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    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Primary cell cultures obtained from embryos of Mizuchopecten yessoensis (Bivalvia) survived for four months. Although the number of cells progressively decreased during the cultivation, mitotic cells were observed both at the first stages and at the end. A possibility of growing marine invertebrates cells in long term primary culture is discussed.
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    Characterization of endosteal osteoblasts isolated from human maxilla and mandible: An experimental system for biocompatibility tests (1991)
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    Cytotechnology 7 (1991), S. 39-48 
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    ISSN: 1573-0778
    Keywords: cell culture ; endosteal human osteoblasts ; maxilla ; mandible ; titanium ; biocompatibility ; alkaline phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Fragments of cancellous and cortical bone from human maxilla and mandible were cultured by the explant technique. Cells isolated by trypsinization of primary cultures were characterized as osteoblasts on the basis of intracellular alkaline phosphatase activity, the constituents of the extracellular matrix, and response to human parathormone (PTH). In culture, the osteoblasts often gave rise to superposed clumps of large cells whose cytoplasm contained endoplasmic reticulum, numerous mitochondria, vacuoles, and a dense network of intermediate filaments, often at the level of the plasma membrane. In the presence of vitamin C and 1,25-dihydroxyvitamin D3, the osteoblasts produced an extracellular matrix composed of collagen type I and various non-collagenous proteins, including osteocalcin. Biochemical test results were comparable to those reported for osteoblasts of other origins (rat calvaria, human iliac crest), and namely elevated intracellular alkaline phosphatase activity and cAMP accumulation in response to stimulation by human PTH (1–34). Osteoblasts isolated in this manner were cultured in the presence of pure titanium disks to determine the effects of exposure to this metal. Electron microscopy revealed few significant differences in cell growth and specific enzyme activity compared to control osteoblasts grown on plastic dishes, reflecting the excellent biologic and biochemical relationship between the osteoblasts and pure titanium. This experimental system thus appears suitable for biocompatibility studies, and in particular, evaluation of dental implants.
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    Characterization of the Unstirred Water Layer in Caco-2 Cell Monolayers Using a Novel Diffusion Apparatus (1991)
    Springer
    Pharmaceutical research 8 (1991), S. 222-227 
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    ISSN: 1573-904X
    Keywords: Caco-2 ; unstirred water layer ; intestinal permeability ; steroids ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Caco-2 monolayers grown on Transwell polycarbonate membranes have been characterized as a valuable tool in drug transport studies. Despite the clear advantages of this system, the lack of stirring may create an unstirred water layer (UWL) whose resistance may limit the transcellular transport of lipophilic molecules. The objective of this study was to evaluate a novel diffusion cell where the transport buffer is mixed by gas lift and to determine the mixing flow rate needed to reduce the thickness (h) of the UWL adjacent to cell monolayers. The transport of the leakage marker, mannitol, remained at least 15-fold lower than the flux of testosterone, indicating that the stirring flow rates used did not affect the integrity of the monolayers. The permeability (P) of testosterone (log PC 3.13) across monolayers mounted on this diffusion cell was 4.07, 10.90, and 14.18 × 10−5 cm/sec at flow rates of 0, 15, and 40 ml/min, respectively, and the apparent UWLs were calculated to be 1966, 733, and 564µm. P and h in the stagnant Transwell were 3.08 × 10−5 cm/sec and 2597 µm, respectively. On the other hand, h was significantly smaller in the unstirred, cell-free membranes than in their cell-containing counterparts. P was correlated with lipophilicity and, in the case of the more lipophilic compounds, with the mixing flow rate.
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    The Influence of Peptide Structure on Transport Across Caco-2 Cells (1991)
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    Pharmaceutical research 8 (1991), S. 1453-1460 
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    ISSN: 1573-904X
    Keywords: peptide ; transport ; permeability ; lipophilicity ; hydrogen bonding ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The relationship between structure and permeability of peptides across epithelial cells was studied. Using confluent monolayers of Caco-2 cells as a model of the intestinal epithelium, permeability coefficients were obtained from the steady-state flux of a series of neutral and zwitterionic peptides prepared from D-phenylalanine and glycine. Although these peptides ranged in lipophilicity (log octanol/water partition coefficient) from −2.2 to +2.8, no correlation was found between the observed flux and the apparent lipophilicity. However, a strong correlation was found for the flux of the neutral series and the total number of hydrogen bonds the peptide could potentially make with water. These results suggest that a major impediment to peptide passive absorption is the energy required to break water–peptide hydrogen bonds in order for the solute to enter the cell membrane. This energy appears not to be offset by the favorable introduction of lipophilic side chains in the amino acid residues.
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    The use of tuftsin in experimental leprosy (1991)
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    Bulletin of experimental biology and medicine 112 (1991), S. 1152-1156 
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    ISSN: 1573-8221
    Keywords: experimental leprosy ; synthetic tuftsin ; cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00839564
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