Potassium Channels in Eremosphaera viridis: Modulation of Channel Opening, Conductance and Inhibition*

I/V relationships were performed by the voltage clamp technique in the sphaerical green alga Eremosphaera viridis de Bary. We focused on the course of the transient potential (TP) found in light‐off experiments when specific potassium channels open. I/V measurements done during this period show a N‐shaped curve. The shape depended on external potassium. TPs could be released by light‐off and by addition of barium, strontium, or α‐naphthyl phosphate. We calculated the number of specific potassium channels to be between 1750 and 34 825 channels per cell. Barium (1 mol × m−3) and tetraethylammonium (10 mol × m−3) inhibited TPs. I/V relationships demonstrated, when N‐shaped, that potassium channels start to close at voltages more negative than −195 mV (0.1 mol × m−3 K+), −160 mV (1 mol × m−3 K+) and −148 mV (10 mol × m−3 K+). In the region of −300 mV conditions similar to those at rest are reached. External sodium suppressed the development of N‐shaped I/V relationships and reduced the membrane conductance during a TP between 8 % and 29 %. This indicates an influence of external sodium on potassium channels.