Measurements of Electro-osmosis inNitella translucens

Abstract

Determinations of the electro-osmotic efficiency (models H2O per Faraday) in Nitella translucens have been made under different conditions. Associated tracer measurements show that the main path of current flow ins through the cell, and not in the cell wall external to the membrane, but that the measured influxes of Na and K can account for only a small fraction of the current. The electro-osmotic coefficient increases markedly at very low currents in the light (to as high as 700 H2O/F), is decreased in the dark, in the presence of low concentrations of N-dichlorophenyl-N′, N′ -dimethyl urea (DCMU) or of carbonyl cyanide m-chlorophenylhydrazone (CCCP) and on the addition of I mM NaHCO3 to the bathing solution; the efficiency is higher at 10.5 °C than at 22 °C. Electro-osmosis, generated by a difference in membrane potential at the two ends of the cell bathed by different solutions, gave values of the electro-osmotic coefficient similar to those characteristic of low applied currents.The results suggest that the cell membrane, and not only the cell wall, shows electro-osmotic properties. A simplified analysis of the system shows that the electro-osmotic coefficient measured depends on conditions at each end of the cell and is not simply a property of the cation added at the end of the cell at which positive current enters.