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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 166 (1998), S. 213-222 
    ISSN: 1432-1424
    Keywords: Key words: Patch-clamp — Slices — Astrocyte — Voltage-activated channels — Potassium current
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Astrocytes that are recorded in acute tissue slices of rat hippocampus using whole-cell patch-clamp, commonly exhibit voltage-activated Na+ and K+ currents. Some reports have described astrocytes that appear to lack voltage-activated currents and proposed that these cells constitute a subpopulation of electrophysiologically passive astrocytes. We show here that these cells can spontaneously change during a recording unmasking expression of previously suppressed voltage-activated currents, suggesting that such cells do not represent a subpopulation of passive astrocytes. Superfusion of a low Ca2+/EGTA solution was able to reversibly suppress voltage-activated K+ currents in cultured astrocytes. Currents were restored upon addition of normal bath Ca2+. These effects of Ca2+ on both outward and inward K+ currents were dose- and time-dependent, with increasing concentrations of Ca2+ (from 0 to 800 μm) leading to a gradual unmasking of voltage-dependent outward and inward K+ currents. The transition from an apparently passive cell to one exhibiting prominent voltage-activated currents was not associated with any changes in membrane capacitance or access resistance. By contrast, in cells in which low access resistance or poor seal accounted for the absence of voltage-activated currents, improvement of cell access was always accompanied by changes in series resistance and membrane capacitance. We propose that spillage of pipette solution containing low Ca2+/EGTA during cell approach in slice recordings and/or poor cell access, lead to a transient masking of voltage-activated currents even in astrocytes that express prominent voltage-activated currents. These cells, however, do not constitute a subpopulation of electrophysiologically passive astrocytes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1424
    Keywords: Key words: BK channels — Muscarine — Acetylcholine — Calcium — Migration — Tumor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Patients with cerebral tumors often present with elevated levels of acetylcholine (ACh) in their cerebrospinal fluid. This motivated us to investigate physiological effects of ACh on cultured human astrocytoma cells (U373) using a combination of videomicroscopy, calcium microspectrofluorimetry and perforated patch-clamp recording. Astrocytoma cells exhibited the typical morphological changes associated with cell migration; polarized cells displayed prominent lamellipodia and associated membrane ruffling at the anterior of the cell, and a long tail region that periodically contracted into the cell body as the cell moved forward. Bath application of the ACh receptor agonist, muscarine, reversibly inhibited cell migration. In conjunction with this inhibition, ACh induced a dose-dependent, biphasic increase in resting intracellular free calcium concentration ([Ca2+] i ) associated with periodic Ca2+ oscillations during prolonged ACh applications. The early transient rise in [Ca2+] i was abolished by ionomycin and thapsigargin but was insensitive to caffeine and ryanodine while the plateau phase was strictly dependent on external calcium. The Ca2+ response to ACh was mimicked by muscarine and abolished by the muscarinic antagonists, atropine or 4-DAMP, but not by pirenzepine. Using perforated patch-clamp recordings combined with fluorescent imaging, we demonstrated that ACh-induced [Ca2+] i oscillations triggered membrane voltage oscillations that were due to the activation of voltage-dependent, Ca2+-sensitive K+ currents. These K+ currents were blocked by intracellular injection of EGTA, or by extracellular application of TEA, quinine, or charybdotoxin, but not by apamin. These studies suggest that activation of muscarinic receptors on glioma cells induce the release of Ca2+ from intracellular stores which in turn activate Ca2+-dependent (BK-type) K+ channels. Furthermore, this effect was associated with inhibition of cell migration, suggesting an interaction of this pathway with glioma cell migration.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 633 (1991), 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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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 633 (1991), 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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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    FEBS Letters 244 (1989), S. 361-364 
    ISSN: 0014-5793
    Keywords: (Human brain) ; Electrophysiology ; Ligand-gated ion channel ; cDNA cloning ; γ-Aminobutyric acid A receptor
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-4943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 34 (1983), S. 107-111 
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Measurement of iron-pickup by potable water - A new method for the assessment of surface layers in black steel pipingRed water in drinking water distribution systems causes problems for the water companies because of the consumers pretension to get drinking water of high quality. The corrosion products in the water are normally iron compounds, which arise from the corrosion process and diffuse through the surface layer into the aqueous phase. With the proposed method, the increase of the iron concentration in the water and parallel the corrosion rate, by the determination of the differential oxygen demand, is measured. This allows to make direct statements with regard to the protective qualities of the surface layer.
    Notes: Das Aufteten von Rostwasser bei der Verteilung von Trinkwasser in Rohrleitungen aus ungeschützten Eisenwerkstoffen gehört zu den Korrosionsproblemen, die im Gegensatz stehen zu dem Anspruch des Verbrauchers auf ein qualitative hochwertiges Trinkwasser. Die Ursachen für diesen Korrosionsschaden sind in der Qualität der sich an der Rohrinnenwandung aufbauenden Deckschicht zu suchen. Mit der hier beschriebenen Methode zur Messung der Aufeisenung wird ein Verfahren vorgeschlagen, das in Verbindung mit der parallel über die Sauerstoffdifferenzmessung zu bestimmenden Korrosionsrate eine direkte Beurteilung der Deckschichtqualitäten hinsichtlich ihrer schützenden Eigenschaften ermöglicht.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 261 (1972), S. 117-123 
    ISSN: 1618-2650
    Keywords: Best. der Beladung von Aktivkohle mit Organ. Verbindungen ; Wasserstoffperoxidzersetzung
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Eine einfache analytische Methode wird beschrieben, mit welcher die Beladung von Aktivkohle mit organischen Stoffen schnell ermittelt werden kann. Das Verfahren beruht auf der Zersetzung von H2O2 durch katalytisch wirkende freie aktive Zentren der Kohle; blockierte Zentren katalysieren nicht. Eine Reihe daraus abgeleiteter analytischer Anwendungsmöglichkeiten wird beschrieben. Aus den Meßergebnissen ergeben sich ferner Informationen über die Art der Bindung zwischen Adsorptiv und Adsorbens sowie über den spezifischen Platzbedarf der Adsorptivmoleküle.
    Notes: Abstract A simple method is described for the rapid determination of the amount of organic substances adsorbed on activated carbon. The technique is based on the catalytic decomposition of H2O2 by free active centres on the carbon; occupied adsorption sites are not catalytically effective. The data yield additional information as to the type of binding between adsorbed substance and adsorbent as well as to the specific space requirement of the adsorbed molecules. A number of possible applications are discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 324 (1986), S. 225-225 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Bei der Erzeugung von vollentsalztem Kesselspeisewasser, bei der Gewinnung von Trinkwasser aus organisch belastetem Rohwasser und bei der Reinigung von Abwasser stellt sich die Aufgabe, die organischen Wasserinhaltstoffe zu entfernen. Für den Anteil der organischen Substanzen, der in ionogener Form vorliegt, lassen sich Ionenaustauschverfahren verwenden. Für die Berechnung einer technischen Anlage werden die Stoffübergangswiderstände und das Gleichgewichtsverhalten des Austauschharzes benötigt. Die vorliegende Arbeit hat das Ziel, die Stoffübergangswiderstände für das System organisches Anion/makroporöses Ionenaustauschharz zu ermitteln. Es zeigt sich, daß der Stoffübergangswiderstand in der flüssigen Phase nicht vernachlässigt werden darf. Darüber hinaus läßt er sich mit den bekannten Gleichungen des Wärme- und Stoffübergangs beschreiben.
    Additional Material: 6 Ill.
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