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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 147 (1995), S. 121-136 
    ISSN: 1432-1424
    Keywords: Chloride channel ; Cardiac sarcoplasmic reticulum ; Planar lipid bilayer ; Ion selectivity ; Voltage ; Block ; pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We have characterized a voltage-sensitive chloride channel from cardiac sarcoplasmic reticulum (SR) following reconstitution of porcine heart SR into planar lipid bilayers. In 250 mm KCl, the channel had a main conductance level of 130 pS and exhibited two substrates of 61 and 154 pS. The channel was very selective for Cl− over K+ or Na+ ( $$P_{{\text{K}}^{\text{ + }} } /P_{{\text{Cl}}^{\text{ - }} } = 0.012$$ and $$P_{{\text{Na}}^{\text{ + }} } /P_{{\text{Cl}}^{\text{ - }} } \sim 0.040$$ ). It was permeable to several anions and displayed the following sequence of anion permeability: SCN− 〉 I− 〉 NO 3 − ∼ Br− 〉 Cl− 〉 f− 〉 HCOO−. Single-channel conductance saturated with increasing Cl− concentrations (K m= 900 mm and γmax = 488 pS). Channel activity was voltage dependent, with an open probability ranging from ∼1.0 around 0 mV to ∼0.5 at +80 mV. From −20 to +80 mV, channel gating was time-independent. However, at voltages below −40 mV the channel entered a long-lasting closed state. Mean open times varied with voltage, from ∼340 msec at −20 mV to ∼6 msec at +80 mV, whereas closed times were unaffected. The channel was not Ca2+-dependent. Channel activity was blocked by disulfonic stilbenes, arylaminobenzoates, zinc, and cadmium. Single-channel conductance was sensitive to trans pH, ranging from ∼190 pS at pH 5.5 to ∼60 pS at pH 9.0. These characteristics are different from those previously described for Cl− channels from skeletal or cardiac muscle SR.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 67 (1998), S. 239-248 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary Unbeknownst to many fruit and vegetable producers a killer frost sneaked down the Florida peninsula during the night of January 18 to 19, 1997. According to news reports in left in its wake approximately $ 200 million in damage to crops and tress, much of which could have been avoided with available abatement technology. A lot of finger pointing followed between victims and agencies trying to fix the blame on an identifiable culprit. The recent privatization of some of the National Weather Service's former responsibilities added fuel to the fire. Without touching these politically “hot potatoes” the present paper gives a brief account of observational facts and then describes the results from an inexpensive, PC-based, operational forecasting system. That system has been described earlier (Reiter, 1991; Teixeira and Reiter, 1995; Reiter et al., 1998). The advantage of a “hybrid” system in which the user can interact with, and modify, the forecast “on the fly” is demonstrated.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 125 (2000), S. 119-126 
    ISSN: 1432-1939
    Keywords: Key words Disturbance ; Patch dynamics ; Stream ecology ; Bed stability ; Mobile species
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The patchy distribution of benthic invertebrates in streams and rivers is an important and widely researched phenomenon. Previous studies on reasons for this patchiness have neglected the potential role of local disturbance history, probably because most lotic invertebrates are mobile and any effect of disturbance history was thought to be short-lived. Here we demonstrate for a New Zealand gravel-bed stream that local disturbance history can have long-term effects on the distribution of highly mobile stream invertebrates. Buried scour chains (100 at each of three 20-m sites within a 350-m reach) indicated that a spate with a return period of 5 months caused a mosaic of bed patches with different stabilities. More than 2 months after the spate, we took random, quantitative samples at each site from five patches that had experienced 4 cm or more of scour during the spate, from five patches with 4 cm or more of fill, and from five stable patches. Density of the dominant invertebrate taxon, the highly mobile mayfly Deleatidium spp., and densities of another three of the seven most common taxa differed significantly between patch stability categories. Larvae of Deleatidium, the black fly Austrosimulium spp. and the dipteran Eriopterini were most abundant in fill patches, whereas Isopoda were most abundant in scour patches. Total invertebrate densities and densities of six common taxa also differed between sites, although these were only 95–120 m apart. These results show that local disturbance history can have long-term effects on lotic invertebrates and be an important cause of invertebrate patchiness. The observed effects might have been even stronger had we sampled sooner after the spate or after a large flood. Disturbance history may influence invertebrates both directly (through dislodgement or mortality) and indirectly, through effects on the spatial distribution of their resources. Our results suggest that the role of disturbance in structuring animal communities dominated by mobile species may be more important than previously thought.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 38 (1979), S. 231-234 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Investigational new drugs 4 (1986), S. 337-345 
    ISSN: 1573-0646
    Keywords: heterogeneity ; polyamines ; cell killing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract The effects of αDifluoromethylornithine (DFMO)2 on survival of human gastric cancer clones were studied in vitro. The responses were dose and time dependent. Treatments which lasted for less than 12 h were cytotoxic at only the highest doses used. The greatest effects on survival were observed only when cells were treated for 48 and 72 h. The effects on the clones produced by such prolonged treatment durations were heterogeneous, with survival values differing by as much as 460%. By contrast, the clonal survival responses to short DFMO treatments (12 h) were very uniform (dose differential of only 19%); however, this uniformity in response could be achieved only by using non-pharmacological doses of DFMO. The heterogeneity in survival responses in the clones might be slightly associated with their levels of intracellular spermidine. Clones with the smallest amounts of intracellular spermidine at the start of treatment were most sensitive to DFMO. However, this association may not hold up with further testing in other gastric cancer clones or when studied in other cancer lines in vitro.
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  • 6
    ISSN: 1573-0646
    Keywords: heterogeneity ; polyamines ; cell killing ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract The effects of α-difluoromethylornithine (DFMO) on survival, cell kinetics and polyamine levels were studied on two clones of human astrocytoma in vitro. The survival responses were dose and time dependent; and treatments with DFMO which lasted for 72 h resulted in heterogeneous responses with one clone being up to 6 times more sensitive than the other. Shorter treatments produced more uniform killing in the clones. A continuous exposure of the cells to 5 mM DFMO resulted in a rapid decrease in putrescine values in both clones, followed by decreases in the spermidine levels. These effects were closely followed by 148% to 170% increases in cell population doubling times, and a lowering of saturation densities. No clear correlations could be established among baseline polyamine levels and cell kinetics or survival responses to DFMO treatments.
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  • 7
    ISSN: 1573-0646
    Keywords: heterogeneous human tumor clones ; differential drug sensitivities ; uniform killing ; sensitivity ; resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Four permanent clones of a human adenocarcinoma of the stomach and the parent line from which they were isolated were used as an in vitro model system to evaluate the effects of 8 anticancer agents on cell survival. The drugs tested were actinomycin D (Act-D), Bleomycin (Bleo), adriamycin (adria), melphalan, chlorambucil, 5 Fluorouracil (5FU), 1,2:5,6-Dianhydrogalactitol (DAG), and 1-(2-chloroethyl)-3-(4-methyl cyclohexyl-1-nitrosurea) (MeCCNU). Although the cell lines had similar growth properties, morphologies and modal chromosome numbers, the clones expressed heterogeneous survival responses to each of six drugs tested. A comparison of the doses lethal to 90% of a clonal population (LD90) for each drug indicated large differences between the most sensitive and least sensitive clones. For chlorambucil there was a 160% difference between the LD90 values of the most and least sensitive clones. For MeCCNU the difference was 200%; for adria, 230%; Bleo, 280%; 5FU, 360%; and melphalan, 600%. Despite the heterogeneity in response among the clones to these agents, no particular clone was always the most sensitive or resistant. Of particular interest was the finding that these stomach cancer clones demonstrated uniform responses to both Act-D and DAG. Since the differential drug sensitivities expressed by heterogeneous tumor populations could be a cause of treatment failure in the patient, the demonstration of uniform sensitivities to Act-D and DAG are encouraging and suggest that other anticancer drugs which produce uniform cell killing may be identified and tested. Act-D and adria were the most effective of the drugs tested when compared on a dose for dose basis. Both agents killed more than 99.9% of the parent cell line with doses below 3μg/ml (1-h treatments). The cells were least sensitive to 5FU, with only 30% of the cells killed at 100 μg/ml. The studies reported here indicate that this human stomach cancer model can provide valuable insight into the design of clinical protocols for treatment of gastric carcinoma in man.
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  • 8
    ISSN: 1573-0646
    Keywords: glutathione ; heterogeneity ; gastric cancer ; resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Permanent cell lines and clones established from an untreated patient (AGS cells) with gastric carcinoma, and from a similar patient who had been treated with Adriamycin, 5FU and cytoxan (SII cells) were used in a study that compared their drug and radiation survival sensitivities to their glutathidine (GSH) values. The SII parental cell line was more resistant than the AGS cells in vitro to chlorambucil, ACT D, Adria, Bleo, and X-rays. This greater resistance was positively correlated with GSH values that were 1.77 times higher than in the AGS parental cell line. By contrast the SII parental cells were more sensitive than the AGS cells to MeCCNU and Melphalan. The drug and radiation sensitives expressed among the clones of the two cell lines were heterogeneous and did not correlate with their GSH values.
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  • 9
    ISSN: 1573-0646
    Keywords: DFMO ; human stomach cancer ; cell kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract Treatment of human gastric cancer clones in vitro with low doses of DFMO (5 mM) produced elongation of the cell population doubling times and lowering of the saturation densities. By contrast, DFMO treatment of normal human skin fibroblasts altered only the saturation density. The lack of an effect of 5 mM DFMO on the doubling time of normal fibroblasts may be directly related to baseline intracellular putrescine levels, which were about 2.5 times higher than in the cancer cells. The same dose of DFMO caused a rapid decrease in intracellular polyamine levels in the tumor clones. The effects on the doubling time and saturation density were almost totally abolished by the addition of 50 μM putrescine to the growth medium during the first 24 h of treatment with DFMO. Exposure to 5 mM DFMO for 24 h caused the human gastric cancer cells to become blocked in G1 phase only, and this led to a reduction in the fraction of cells in S phase. The G1 block was reversible and this cohort of cells eventually passed through S phase and then through G2 and M. A higher 100 mM dose of DFMO and longer exposure times for both doses produced cell cycle changes and death of more than 90% of the cell population. These data suggest that cell kinetics changes observed under these experimental conditions may reflect polyamine-related alterations in the biochemical events of cell cycle progression kinetics; but may also be the result of DFMO-induced loss of cell viability.
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  • 10
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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