A membrane defect in cystic fibrosis: decreased red cell permeability to water

The abnormally high concentrations of electrolytes and organic solutes found in the glandular secretions of individuals with cystic fibrosis may arise from decreased water content rather than perturbed solute transport. Thus, it is possible that the abnormalities insolute concentrations are a result of a reduced water movement into the secretory product. It is our hypothesis that if an abnormality exists in the transport of water across secretory cell membranes, this defect may also be expressed in nonsecretory cell membrane permeability to water. We report here osmotic water permeability measurements on red cells and 11 cystic fibrosis patients ranging in age from 2 to 20 years and eight normal individuals. The mean hydraulic conductivity for the patients of 1.23 +/- 0.13 cm3/dyne sec is significantly less (P < 0.001) than that of normal individuals who have permeabilities of 1.45 +/- 0.11 cm3/dyne sec. Analysis showed that the osmotic water permeability correlates well with the Shwachman score (r = 0.76). Patients who are in the poorest clinical condition show the lowest hydraulic conductivities.