Diffusional (Pw) and osmotic (Pf) water permeability coefficients were determined for the syncytial epithelium of larval Echinococcus granulosus. Pw was calculated from simultaneous influx measurements of tritiated water and n-[14C]butanol through the hydatid cyst wall. The total diffusional water permeability coefficient, P'w, was found to be 2.2 X 10(-4) cm s-1; which is similar to that previously reported by Rotunno et al. (1974, J. Parasitol. 60, 13-620). Nevertheless, when P'f is corrected for the unstirred water layer effects, a Pw value of 6.2 X 10(-4) cm s-1 is obtained. Thus, the unstirred water layer effects have a very important contribution to P'w. Total steady state osmotic permeability coefficient, P'f, was bound to be about 15 X 10(-4) cm s-1 and it is scarcely affected by those mechanisms that tend to distort the evaluation of Pf. The experimentally determined osmotic coefficient differs from the corrected Pf by only 6%. The Pf/Pw ratio was found to be 2.4. The present study clearly confirms that syncytial membranes can be highly permeable to water, in spite of the fact that they lack tight junctions. Thus, water permeability through epithelial syncytium must be exclusively controlled by the permeability of the apical and/or basocellular membranes.
Animals Ascitic Fluid