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  • 1
    Electronic Resource
    Electronic Resource
    Potassium channels in Eremosphaera viridis (1986)
    Springer
    Planta 167 (1986), S. 66-75 
    Details
    ISSN: 1432-2048
    Keywords: Action potential and pH transient ; Chlorophyta ; Eremosphaera ; Plasma membrane (I/V-curves) ; Potassium channel ; Signal transfer ; Voltage and current clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To characterize the assumed potassium channels in the plasma membrane of the green alga Eremosphaera viridis (Köhler et al. 1985), current-voltage (I/V)-curves under resting conditions and during an action-potential-like response (CAP) were constructed using voltage- and current-clamp techniques. Under resting conditions the I/V-curves of Eremosphaera showed a distinct upward bending when approaching zero mV, a nearly straight line in the medium part and a downward bending during strong hyperpolarization. Measurements in light and darkness frequently displayed a parallel shift of the I/V-curve in the middle part, indicating a current source which is slowed down by light-off. Using the voltage-clamp technique, N-shaped I/V-curves were sometimes observed. The potassium concentration outside influenced the downward-bending part of the I/V-curve whereas the tetraethylammonium cation, known to block potassium channels, reduced the upward-bending part in particular. A change in external pH, either to pH 7 or pH 3.1 from a standard pH 5.5, caused an increase in conductivity. Chemically induced action potentials were released in Eremosphaera under voltage-clamp conditions by light-off and there was both a current flow and an increase in conductivity during the CAP. Clamping the membrane potential at a value more negative than Nernst potential of potassium revealed an inward current, whereas clamping at a more-positive value revealed an outward current. The experiments demonstrate that there is no threshold potential in releasing a CAP. The I/V-curves performed under current clamp at the peak of CAP verify a previously found increased conductivity with hyper- or depolarization depending on the external potassium concentration. These experiments provide further evidence that in Eremosphaera potassium channels are involved in the CAP caused by a light-off signal. Additional experiments indicate that after light-off a transient acidification of the cytoplasm takes place in correlation with the CAP and the opening of potassium channels. A preliminary “battery model” is discussed to understand the role of potassium channels during a CAP in pH-regulation of the cytoplasm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00446370
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  • 2
    Electronic Resource
    Electronic Resource
    Potassium channels in Eremosphaera viridis (1985)
    Springer
    Planta 166 (1985), S. 490-499 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyta ; Eremosphaera ; Membrane potential and resistance (light-dependent) ; Light and membrane potential ; Potassium channel ; Signal transfer ; Transient (membrane potential)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dependence of the membrane potential of Eremosphaera viridis on different external concentrations of potassium, sodium, calcium, and protons was compared with the diffusion potential measured in the dark and in the presence of NaN3. In contrast to some other algae, the membrane potential in the light as well as in the dark seemed to be predominantly determined by the calculated diffusion potential and less by an electrogenic pump which, however, seemed to be involved at potassium concentrations 〉1 mol·m-3 and at higher pHos (〉pH 6). Furthermore, some characteristics of an action-potential-like response (CAP) triggered by light-off, and independent of the membrane-potential threshold value, were determined. The CAP had a delay period of 5.4 s and needed 4.5 s for polarization to a plateau. On average, the plateau held for 8.8 s and the CAP lasted 37.7 s. The peak amplitudes of CAP (P AP) exactly followed the Nernst potential of potassium. Other cations like sodium, calcium and protons did not appreciably affect the peak amplitudes of CAP. From these and other results it can be assumed that the CAP is caused by a temporary opening of potassium channels in the plasma membrane of Eremosphaera (Köhler et al., 1983, Planta 159, 165–171). The release of a CAP by light-off has been partly explained by the participation of a transient increase of proton concentration in the cytoplasm. It was possible to trigger a CAP by external pH changes and by the addition of sodium acetate, thus supporting the hypothesis that a pH decrease in the cytoplasm may be one element of the signal transfer from the photosynthetic system to the potassium channels in the plasmalemma. Calcium also seemed to have an influence on triggering the CAP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391273
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  • 3
    Electronic Resource
    Electronic Resource
    Zur Koordinationschemie des 1,3-Dithiol-2-thion-4,5-diselenolats (dsit) - ein Vergleich mit 1,3-Dithiol-2-thion-4,5-dithiolat (dmit) (1989)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 577 (1989), S. 206-216 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Coordination Chemistry of 1,3-Dithiole-2-thione-4,5-diselenolate (dsit)  -  Comparison with 1,3-Dithiole-2-thione-4,5-dithiolate (dmit)Synthesis and properties of metal(II) and/or metal(III) bis-chelates of 1,3-dithiole-2-thione-4,5-diselenolate (dsit) of general type (Bu4N)n[M(dsit)2] (n = 2: M = Zn, Cd, Hg, Cu, Ni, Pd, Pt; n = 1: M = Ni, Au) are described. By comparison of the ir, 13C nmr, epr spectra, cyclovoltammetric data, and x-ray investigations (nickel-bis-chelates) of chelates of dsit and those of the chelates of 1,3-dithiole-2-thione-4,5-dithiolate (dmit) the consequences of selenium for sulfur substitution on position 4 and 5 of the heterocyclic ligand are discussed.
    Notes: Synthese und Eigenschaften von Metall(II)- und/oder Metall(III)-Bis-Chelaten des 1,3-Dithiol-2-thion-4,5-diselenolats (dsit) vom Typ (Bu4N)n[M(dsit)2] (n = 2: M = Zn, Cd, Hg, Cu, Ni, Pd, Pt; n = 1: M = Ni, Au) werden beschrieben. Anhand der IR-, 13C-NMR-, EPR-Spektren, Cyclovoltammogramme und röntgenographischen Untersuchungen der Nickel-Bis-Chelate werden die Auswirkungen der Substitution von Schwefel durch Selen an der 4- und 5-Position diskutiert.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19895770123
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  • 4
    Electronic Resource
    Electronic Resource
    Zum Ligandenaustausch an TcNX4--Komplexen (X = Cl, Br) (1987)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 544 (1987), S. 167-180 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Ligand-Exchange Reactions on TcNX4- Complexes (X = Cl, Br)Ligand exchange reactions on the nitridotechnetium(VI) compounds (Bu4N)TcNCl4 and (Bu4N)TcNBr4 are reported. The use of various organic ligands having different donor atom sets produces TcV nitrido complexes. The reaction of (Bu4N)TcNCl4 with (Bu4N)TcNBr4 is characterized by the formation of TcVI complex species with mixed Cl/Br coordination spheres. EPR detection of the mixed-ligand complexes results in a well-defined dependence of the EPR parameters on the composition of the first coordination sphere of the complexes.
    Notes: Es wird über Ligandenaustauschreaktionen an den Nitridotechnetium(VI)-Komplexen (Bu4N)TcNCl4 und (Bu4N)TcNBr4 berichtet. Dabei entstehen bei Verwendung organischer Liganden mit unterschiedlichen Donoratomen Nitridokomplexe des Technetiums(V). Bei der Reaktion von (Bu4N)TcNCl4 mit (Bu4N)TcNBr4 in unterschiedlichen Mischungsverhältnissen entstehen Komplexspezies des TcVI mit gemischter Cl/Br-Koordinationssphäre. Bei Untersuchungen mittels EPR-Spektroskopie konnte für die gebildeten Gemischtligandkomplexe eine definierte Abhängigkeit der Spektrenparameter von der Zusammensetzung der ersten Koordinationssphäre nachgewiesen werden.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19875440118
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  • 5
    Electronic Resource
    Electronic Resource
    EPR-Untersuchungen an Vanadylkomplexen (1987)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 544 (1987), S. 215-224 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: EPR Examination of Vanadyl ComplexesFor a series of bidentate ligands the reaction with VOSO4 · 3 H2O was studied in homogeneous solution. The resulting complexes were examined by EPR spectroscopy in chloroform at T = 295 and 133 K to receive evidence of the redox behavior of the compounds and of bonding relations in the first coordination sphere in dependence on the equatorial donor atoms.
    Notes: Eine Reihe zweizähniger Chelatbildner wird in homogener Phase mit VOSO4 · 3 H2O umgesetzt. Die gebildeten Komplexe werden EPR-spektroskopisch in Chloroform bei T = 295 und 133 K untersucht und Aussagen zur Redoxanfälligkeit der Komplexe und zu den Bindungsverhältnissen der ersten Koordinationssphäre in Abhängigkeit von den äquatorialen Donoratomen abgeleitet.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19875440123
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