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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 184 (1985), S. 23-31 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Lifelike models of the oscillating legs treated as three-segment systems show the course of kinetic and potential energy over the locomotor cycle for a cheetah, pronghorn, jackrabbit, and elephant running at speeds approaching their maxima. The models can be adjusted to eliminate differences among the animals in time intervals, mass or length of limb, and joint angles. This facilitates analysis of the influence on total energy of each of these variables and of the distribution of mass among leg segments. Fast-cycling legs of the carnivore type have significantly more energy than those of the hoofed type. This may contribute to the lesser endurance that is usual for carnivores that hunt using a high-speed dash.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0730-2312
    Keywords: gene regulation ; 2,3,7,8-tetrachlorodibenzo-p-dioxin ; cytochrome P1-450 ; receptor ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) dioxin, produces a diverse set of biological responses which, in some cases, reflects the altered expression of specific genes. An intracellular receptor protein binds TCDD saturably and with high affinity and mediates several of TCDD's biological effects. In mouse hepatoma cells, TCDD induces aryl hydrocarbon hydroxylase activity by activating the transcription of the cytochrome P1-450 gene. Studies of receptor-defective variant cells indicate that the activation of cytochrome P1-450 gene transcription requires functional TCDD receptors. Analysis of the DNA that flanks the 5′-end of the mouse cytochrome P1-450 gene reveals at least three control regions: a promoter, an inhibitory element, and a dioxin-responsive element (DRE). Therefore, expression of the cytochrome P1-450 gene represents a balance between negative and positive control. The DRE contains two discrete, non-overlapping DNA domains that respond to TCDD. Each TCDD-responsive domain acts independently of the other, each requires TCDD receptors for function, and each has the properties of a transcriptional enhancer. For example, the function of the DREs is relatively independent of both their location and their orientation with respect to the promoter. Together, the DREs and the TCDD-receptor complex constitute a dioxin-responsive enhancer system. Exposure of cells to TCDD results in the protection of a specific DNA domain from exonuclease digestion. This protection requires TCDD receptors. The protected domain maps to a DRE. This observation implies that the TCDD-receptor complex interacts with the DRE to activate the transcription of the cytochrome P1-450 gene.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0730-2312
    Keywords: EGF receptor ; multidrug-resistance ; human neuroblastoma ; binding assay ; immunoprecipitation ; transformation/differentiation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Multidrug-resistant human neuroblastoma cell lines obtained by selection with vincristine or actinomycin D from two independent clonal lines, SH-SY5Y and MCIXC, have 3- to 30-fold more cell surface epidermal growth factor (EGF) receptors than the drug-sensitive parental cells as indicated by EGF binding assays and immunoprecipitation, affinity-labeling, and phosphorylation studies. Reversion to drug sensitivity in one line was accompanied by a return to the parental level of EGF receptor. SH-EP cells, a clone derived from the same neuroblastoma cell line as SH-SY5Y but which displays melanocyte rather than neuronal lineage markers, also express significantly more EGF receptor than SH-SY5Y cells. By nucleic acid hybridization analysis with a molecularly cloned probe, increased receptor level in multidrug-resistant cells was shown to be the result of higher levels of EGF receptor mRNA in drug-resistant than in drug-sensitive cells. The increased steady state amount of specific RNA did not result from amplification of receptor-encoding genes. A small difference was observed in the electrophoretic mobility under denaturing conditions of EGF receptor immunoprecipitated from drug-resistant and drug-sensitive cells. Quantitative and qualitative modulation of the EGF receptor might reflect alterations in the transformation and/or differentiation phenotype of the resistant cells or might result from unknown selective pressures associated with the development of multidrug resistance.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The influence of age and food restriction on kidney protein synthesis was studied in Fischer F344 rats. The rate of total protein synthesis by suspensions of kiney cells declined 60% between 4 and 31 months of age. The rate of protein synthesis by kidney cells isolated from 19-month old rats fed a restricted diet (60% of diet consumed by rats fed ad libitum) was 45% higher than the rate of protein synthesis by kidney cells isolated from 19-month old rats fed ad libitum. The excretion of protein in the urine was measured to assess the effect of the age related decline in protein synthesis on kidney function. A dramatic increase in proteinuria was observed with increasing age, and rats fed the restricted diet excreted significantly less protein in the urine than rats fed ad libitum.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Bovine fetal aortic endothelial cells cultured in serum-containing medium accumulate angiotensin I-converting enzyme (ACE) activity and also release it into the culture medium. Following subcultivation of a confluent culture using trypsin-EDTA, cellular ACE activity falls 50% within 8 h, but no ACE activity is detected in the medium, suggesting intracellular loss of the enzyme activity. ACE activity reappears in both the cell lysate and culture medium after the culture becomes confluent. The rate of accumulation of ACE activity released into the medium is always greater than that for cellular activity. For example, 21 days following subcultivation 80-85% of the total culture activity is detected in the medium. Both cellular and medium-associated ACE decrease proportionately as the culture progresses through its in vitro lifespan.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 138 (1989), S. 384-392 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A basic understanding of the recruitment of quiescent tumor cells into the cell would be an important contribution to tumor biology and therapy. As a first step in pursuing this goal, we have investigated the regrowth kinetics of cells from different regions in multicellular spheroids of rodent and human origin. Cells were isolated from four different depths within the spheroids using a selective dissociation techinque. The outer cells were proliferating and resumed growth after replating with a 0-8-hour lag period, similar to cells from exponentially growing monolayers. with increasing depth of origin, the lag periods prior to regrowth increased to 2-3 times the monolayer doubling time; cells from plateau-phase monolayers showed a lag period of 1-1.5 times the doubling period. After resuming grwoth, all cells of a given cell line grew with the same doubling time and achieved the same confluency level. The inner spheroid cells and cells from plateau-phase monolayers had reduced clonogenic efficiencies. The inner cells were initially 1.5-3 times smaller than the outer cells, but began to increase in volume within 4 hours of replating. The fractions of S-phase cells were greatly decreased with increasing depth of origin in the spheroids; there were long delays prior to s-phase recovery after plating, to a maximum of 1-1.5 times the normal doubling time. These results suggest that those quiescent cells from spheroids and monolayers which are able ot reenter the cell cycle are predominantly in the G1-phase. However, quiescent cells from the innemost spheroid region require approximately twice as long ot enter normal cell cycle traverse as cells from plateau-phase monolayers. The selective dissociation method can isolate very pure populations of proliferating and quiescent cells in a rapid and nonpeturbing manner; this system will be valuable in further characterizing quiescent cells from spheroids.
    Additional Material: 3 Ill.
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  • 7
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Angiotensin I-converting enzyme (ACE) activity was measured in lysates of cloned and uncloned cultures of bovine fetal aortic endothelial cells. The expression of ACE activity in these cells was complex, and influenced by subcultivation, cell density, serum, cumulative population doublings, and clonal heterogeneity. The ACE specific activity at any point in the in vitro lifespan was determined, at least in part, by interaction of these culture variables. After subcultivation to subconfluent densities, cellular ACE specific activity decreased markedly and did not reach detectable levels until cells attained confluent densities. The use of different suppliers' lots of serum in the growth medium resulted in different cellular ACE specific activities. The ACE specific activity decreased as cultures were serially subcultivated, but remained detectable throughout the lifespan, suggesting a linkage between the proliferative history of an endothelial cell and its remaining capacity to express ACE. Increased ACE activity was observed when cells at the end of their lifespan were cultured at high densities. Cloned strains behaved similarly to the uncloned parent culture, except that they exhibited a wide range of ACE specific activities.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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