Water permeation in Madin-Darby canine kidney cells is modulated by membrane fluidity

Simultaneous determinations of water and antipyrine permeations in monolayers of Madin-Darby canine kidney (MDCK) cells grown on a permeant support were done to study the relationships between water transport and membrane fluidity in these epithelial cells. The changes in permeation of the lipophilic non-electrolyte antipyrine were used to probe the modifications in membrane fluidity. In controls, the apparent diffusional permeability coefficient for water (PDw) was three times higher than the antipyrine's one, PDAp (4.2.10(-5) vs. 1.4.10(-5) cm s-1). Addition of vasopressin or dibutyryl cyclic AMP to the monolayers induced a biphasic increase in antipyrine permeation with peak values at t = 2 min, 3-4-fold that of controls. Variations in water permeation were of similar amplitude and obeyed the same time course, leaving the water to antipyrine permeation ratios unchanged. Compound H7, an inhibitor of protein kinases, blunted the increase in permeation for both antipyrine and water. Finally, addition of the fluidizing agent benzyl alcohol to the monolayers resulted in a parallel increase in PDAp and PDw. These results suggest that the physical state of membrane lipids may control water permeation in MDCK cells.