Effects of sodium, potassium and chloride ions on the membrane potential of Valonia aegagropila

Changes of the resting potential of Valonia cell in sea wateragainst a 10-fold increase of the external concentrations ofK^$, Na^$ and Cl^– were 1±1, 6.2±0.1 and 38.9±4mV, respectively. The potassium conductance was smaller than7 µ/cm², while the Na and Cl conductances were 45 and281 µ/cm², respectively, in normal sea water. The positivevacuolar potential could be explained by these ionic conductances.On the other hand, the membrane became more sensitive to K^$,if the cell was incubated for about 30 min in K-rich (100 mM)sea water. It is worth noting, however, that the membrane conductancewas lower in the K-rich sea water than in the normal sea water. (Received October 7, 1974; )