Oscillations in Extracellular Current, External pH and Membrane Potential and Conductance in the Alkaline Bands ofNitellaandChara

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Abstract
Oscillations with a period of approximately 2 min were observed in the membrane potential of Chara and Nitella upon illumination of dark-treated cells, as well as in the extracellular current pattern and pH values. A 2-min oscillation in the membrane potential was observed when the voltage electrode was placed close to the border of an alkaline and acid region. Comparison of results from Chara and Nitella revealed an identical control mechanism for external pattern stabilization in the effect of light on membrane potential and conductance. Vibrating probe experiments indicated that oscillations in the extracellular current occurred only at the border of the alkaline band. Ion-specific pH micro-electrodes placed within the alkaline band detected oscillations associated with light reactivation of the banding phenomenon. These results indicate that the oscillations represent a localized phenomenon involving spatially-dependent time-constants. More evidence for the spatial dependence of time constants is gained from single active acid regions in Nitella. Using this combination of techniques, we have established that a light-dependent H+ transporter is involved in this oscillation. Current-voltage curves taken during these oscillations and relaxation, after changing the light intensity, confirmed this identification.

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