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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 560 (1989), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 26 (1990), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : Five small (4 ha) forested watersheds in East Texas were instrumented in December 1980 to determine the effect of forest harvesting, mechanical site preparation, and livestock grazing on stormflow, peak discharge rate, and sediment loss. After three pretreatment years, four of the watersheds were treated as follows: (1) clearcutting followed by roller chopping; (2) clearcutting following by shearing and windrowing; (3) clearcutting following by shearing, windrowing, and continuous grazing; and (4) clearcutting followed by shearing, windrowing, and rotational grazing. Clearcut harvesting and all site preparation treatments significantly increased stormflow, peak discharge, and sediment losses over the undisturbed condition. Roller chopping and shearing/windrowing had little impact on sediment loss from these watersheds and appears to be a sound forest conservation practice for gently sloping watersheds (〉 8 percent). As applied, livestock grazing had minimal impact on stormflow and peak discharge. The moderately stocked continuously grazed treatment had little impact on sediment loss, but the high stocking density of the rotational grazing treatment increased sediment losses over the undisturbed condition. Sediment losses from these intensively managed forest watersheds, even though significantly greater than from undisturbed conditions, were within the range of sediment losses from undisturbed watersheds in the Southeast, below the range of losses from mechanically prepared watersheds elsewhere, and well below potential losses from pasture and cropland.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 28 (1992), S. 0 
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : Effects of long-term prescribed burning on infiltration and interrill erosion were assessed on two longleaf pine-bluestem sites in Louisiana. Treatments represented biennially-applied winter, spring, or summer burning on an upland sandy loam site for 20 years; and annual winter or spring, and biennial winter or spring burns on a bottomland silt loam site for 10 years, with unburned controls. Immediate effects of burning were a reduction in surface cover, exposing soil to raindrop impact. Burning the sandy loam site increased interrill erosion after winter and spring treatments, but produced no immediate changes in infiltration capacity or time to runoff irrespective of treatment season. Rapid recovery of under-story vegetation mitigated soil exposure. Biennial burning did not increase interrill erosion, or reduce infiltration capacity and time to runoff on the sandy loam site after 20 years. A complete herbaceous understory covered the silt loam site two years after treatment. Interrill erosion was not significantly increased, or infiltration capacity and time to runoff decreased on burning treatments than unburned controls on the silt loam site. Litter biomass was important in predicting interrill erosion. No surface cover condition could be linked to variability in infiltration capacity. This study provides evidence for the resiliency of a longleaf pine-bluestem association to prescribed burning.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 197 (1963), S. 472-473 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] HAEMOGLOBIN from the red cells of normal persons when separated by electrophoresis at alkaline pH. is not homogeneous. Rather, it consists of three components: the major fraction, haemoglobin A15 constituting about 90 per cent; the slow minor component, haemoglobin A2, constituting 2-3 per cent; ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 85 (2003), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Prolonged hypoxia exerts profound effects on cell function, and has been associated with increased production of amyloid β peptides (AβPs) of Alzheimer's disease. Here, we have investigated the effects of chronic hypoxia (2.5% O2, 24 h) on capacitative Ca2+ entry (CCE) in primary cultures of rat type-I cortical astrocytes, and compared results with those obtained in astrocytes exposed to AβPs. Chronic hypoxia caused a marked enhancement of CCE that was observed after intracellular Ca2+ stores were depleted by bradykinin application or by exposure to thapsigargin (1 µm). Exposure of cells for 24 h to 1 µm AβP(1−40) did not alter CCE. Enhancement of CCE was not attributable to cell hyperpolarization, as chronically hypoxic cells were significantly depolarized as compared with controls. Mitochondrial inhibition [by FCCP (10 µm) and oligomycin (2.5 µg/mL)] suppressed CCE in all three cell groups, but more importantly there were no significant differences in the magnitude of CCE in the three astrocyte groups under these conditions. Similarly, the antioxidants melatonin and Trolox abolished the enhancement of CCE in hypoxic cells. Our results indicate that chronic hypoxia augments CCE in cortical type-I astrocytes, a finding which is not mimicked by AβP(1−40) and appears to be dependent on altered mitochondrial function.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 79 (2001), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Microfluorimetric measurements of intracellular calcium ion concentration [Ca2+]i were employed to examine the effects of chronic hypoxia (2.5% O2, 24 h) on Ca2+ stores and capacitative Ca2+ entry in human neuroblastoma (SH-SY5Y) cells. Activation of muscarinic receptors evoked rises in [Ca2+]i which were enhanced in chronically hypoxic cells. Transient rises of [Ca2+]i evoked in Ca2+-free solutions were greater and decayed more slowly following exposure to chronic hypoxia. In control cells, these transient rises of [Ca2+]i were also enhanced and slowed by removal of external Na+, whereas the same manoeuvre did not affect responses in chronically hypoxic cells. Capacitative Ca2+ entry, observed when re-applying Ca2+ following depletion of intracellular stores, was suppressed in chronically hypoxic cells. Western blots revealed that presenilin-1 levels were unaffected by chronic hypoxia. Exposure of cells to amyloid β peptide (1–40) also increased transient [Ca2+]i rises, but did not mimic any other effects of chronic hypoxia. Our results indicate that chronic hypoxia causes increased filling of intracellular Ca2+ stores, suppressed expression or activity of Na+/Ca2+ exchange and reduced capacitative Ca2+ entry. These effects are not attributable to increased amyloid β peptide or presenilin-1 levels, but are likely to be important in adaptive cellular remodelling in response to prolonged hypoxic or ischemic episodes.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 232 (1974), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 165 (1969), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-2013
    Keywords: Key words ( ; )-BayK 8644 ; Ca2+ current ; Endothelin ; Patch-clamp ; Sarafotoxin 6c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In this study, we have investigated the effect of the vasoconstrictor peptide endothelin-1 (ET-1) on voltage-sensitive Ca2+ channels in rat cerebellar granule neurones using the patch-clamp technique. Using amphotericin B perforated-patch recording of whole-cell currents, the Ca2+ channel current was inhibited by 28.4±6.4% by 400 nM ET-1, but was unaffected when experiments were repeated using the whole-cell, ruptured-patch configuration. In cell-attached patches, 400 nM ET-1 inhibited unitary L-type Ca2+ channel currents (I Ba) by 85±5%. ET-1 decreased the open probability (NP o) and the frequency of channel opening and increased the mean closed time of channels. No effects on the mean open time or the time constants for channel opening or closure were observed. L-type Ca2+ channel inhibition was dose dependent with an IC50 of 19 nM. The effect of ET-1 was prevented by the combined endothelin-A and -B receptor antagonist PD145065 (10 µM), indicating a receptor-mediated effect. The ET-A receptor antagonist BQ-123 (10 µM) prevented Ca2+ channel inhibition by ET-1, while the ET-B receptor agonist sarafotoxin 6c (500 nM) had no effect. The inhibition by ET-1 was not due to a change in the voltage of channel activation. Fura-2 Ca2+ imaging showed that no substantial rise in intracellular Ca2+ levels occurred during ET-1 application excluding a Ca2+-dependent inhibition of the channels. Thus in cultured rat cerebellar granule neurones, ET-1 inhibits L-type Ca2+ channels via activation of the ET-A receptor. Inhibition may be mediated by an as yet unidentified cytoplasmic second messenger.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-2013
    Keywords: ω-Conotoxin GVIA ; Whole-cell patchclamp ; Mg · ATP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of changing the intracellular concentrations of either free Mg2+ ions ([Mg2+]i) or Mg2+-bound adenosine triphosphate ([Mg · ATP]i) on Ca2+ channel currents were assessed in cultured rat cerebellar granule neurones using the whole-cell patch-clamp technique. Raising [Mg2+]i from 0.06 mM to 1.0 mM inhibited Ca2+ channel currents by approximately 50%. The action of ω-conotoxin GVIA (ω-CgTX), a selective inhibitor of “N”-type Ca2+ channels was also investigated. With increasing [Mg2+]i, the proportion of current irreversibly blocked by ω-CgTX was reduced, and was negligible (approximately 5 pA of current) in the presence of [Mg2+]i values of 0.5 mM or greater. Block of the ω-CgTX-sensitive current accounted for the reduction in total current by concentrations of [Mg2+]i to 0.5 mM. Raising [Mg2+]i had no effect on the rate of decay of Ca2+ currents, but did produce a negative shift in current activation, possibly due to a non-specific interaction with negative surface charge. Altering [Mg · ATP]i from 0.3 to 5.0 mM caused a twofold increase in the size of currents without affecting the proportion of current sensitive to ω-CgTX. [Mg2+]i was also effective in inhibiting the Ca2+ channel current following potentiation by increasing [Mg · ATP]i. These data suggest that ω-CgTX-sensitive current in these cells is selectively inhibited by internal Mg2+ whereas both ω-CgTX-sensitive and -resistant components of current are potentiated by internal Mg · ATP. The mechanism by which Mg2+ inhibits “N”-type channels is unclear, but may involve an open channel block.
    Type of Medium: Electronic Resource
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