Membranes of Valonia ventricosa: Apparent Absence of Water-Filled Pores

Science  10 Nov 1967:
Vol. 158, Issue 3802, pp. 787-788
DOI: 10.1126/science.158.3802.787


Osmotic and diffusional permeabilities to water have been measured in internally perfused cells of Valonia ventricosa. The osmotic and diffusional permeability coefficients for the protoplast are identical, 2.4 x 10-4 centimeter per second. Thus, both osmotic and diffusional flows can occur by the same mechanism, that is, by diffusion; and there is no need to postulate the existence of water-filled pores in the membranes of this cell. Supporting evidence for this conclusion is the absence of solvent-solute interactions, that is, "solvent drag," for water, urea, and methanol crossing the protoplast of Valonia.