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  • 1
    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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    Paper (German National Licenses)
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  • 2
    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
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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