Potentials Developed at a Solution-Cytoplasm Interface in Chara corallina during Rest and Excitation

Abstract

Potentials were measured in cells of C. corcillina between two microelectrodes inserted into the cytoplasm, one filled with concentrated [2 kmol/m3 (E~M)] KC1 and the other filled with various dilute solutions of KC1 or NaCl. It was found that when both electrodes are in the cytoplasm a potential difference between the two electrodes is developed which, at kery low concentrations, varied about 40 mV per tenfold change in concentlation of the dilute electrode. During excitation this potential difference transiently disappears. No significant differences could be detected between the results obtained with KCI- and NaClfilled electrodes. A comparison is made between the experimental results and computer solutions for the Donnan and diffusion potentials expected for electrodes inserted into a fixed negatively charged phase. It was found that the experimental results for the resting state could be reasonably accounted for if the cytoplasm is assumed to be a negative Donnan phase with a fixed negative charge concentration of 0.1-0.2~ in which the chloride ion mobility is reduced to 30% of its free solution value. The results obtained during action potentials would then suggest that excitation is accompanied by a loss of the fixed charges in the cytoplasm and a return of the chloride ion mobility to its free solution value.