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  • 1
    Digitale Medien
    Digitale Medien
    Potassium channels in Eremosphaera viridis (1986)
    Springer
    Planta 167 (1986), S. 66-75 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Action potential and pH transient ; Chlorophyta ; Eremosphaera ; Plasma membrane (I/V-curves) ; Potassium channel ; Signal transfer ; Voltage and current clamp
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00446370
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  • 2
    Digitale Medien
    Digitale Medien
    Potassium channels in Eremosphaera viridis (1985)
    Springer
    Planta 166 (1985), S. 490-499 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Chlorophyta ; Eremosphaera ; Membrane potential and resistance (light-dependent) ; Light and membrane potential ; Potassium channel ; Signal transfer ; Transient (membrane potential)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00391273
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  • 3
    Digitale Medien
    Digitale Medien
    Vacuolar ion currents in the primitive green algaEremosphaera viridis: The electrical properties are suggestive of both the Characeae and higher plants (1994)
    Springer
    Protoplasma 179 (1994), S. 34-45 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Eremosphaera viridis ; Instantaneous current ; Time activated current ; Patch-clamp ; Phylogeny ; Vacuolar membrane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The electrical properties of the vacuolar membrane of the primitive green algaEremosphaera virdis were investigated using the patch-clamp technique. In whole vacuole measurements two types of transport systems with long activation time-constants were identified. The first, showing marked outward rectification, was activated by an increase in the cytosolic calcium concentration. Furthermore, it displayed sensitivity to micromolar concentrations of the anion channel blocker Zn2+ and to acidification of the cytosol. In contrast, the second time-activated current component was almost insensitive to changes in cytosolic pH and was blocked by the potassium channel inhibitor TEA. In addition to these slowly activating current components, the vacuolar membrane contained at least two further transport systems, responsible for an instantaneous current. These two current components were distinguished by their different sensitivity to protons, cytosolic calcium, and TEA. Comparing these electrical properties to those observed in vacuoles of higher plants or in cytoplasmic droplets from characean algae, respectively, it seems thatEremosphaera is intermediate, corresponding to the systematic position of this simple green alga.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01360735
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  • 4
    Digitale Medien
    Digitale Medien
    Laser microsurgery: a versatile tool in plant (electro) physiology (1994)
    Springer
    Protoplasma 178 (1994), S. 1-10 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Elodea densa ; Eremosphaera ; Laser microsurgery ; Lilium longiflorum ; Patch-clamp ; Nicotiana tabacum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary In plant cells the cell wall is a formidable obstacle in many physiological studies such as patch-clamp measurements and cell labelling with antibodies. Enzymatic digestion of the cell wall, in order to release a protoplast, has a number of disadvantages; therefore we worked out an alternative method to gain access to the plasma membrane. The wall of specialized cells from three higher plant species and one unicellular alga were perforated using the focussed UV light of a nitrogen laser. In order to enhance the absorption of the UV light by the walls, a dye was used that binds specifically to cell wall components. Extrusion of the protoplast or parts thereof was controlled by a regulated gradual decrease of the osmolarity of the solution surrounding the cells. Cytoplasmic streaming and chloroplast circulation were maintained in the protoplasts, demonstrating their viability after the wall perforation with the laser. Continuous deposition of new cell wall material by the polar tip of pollen tubes after surgical removal of the wall at the tip is another demonstration of the viability of the cells. Formation of high resistance seals between the plasma membrane and a patch pipet was surprisingly difficult. The role of ‘Hechtian strands’ and continuing synthesis of cell wall material in seal formation is further investigated. Other applications for the surgical laser are: fusion of two cells or vacuoles, analysis of the composition of specific parts of the cell wall, and release of the vacuole from an identified cell type for patchclamp studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01404115
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