Transepithelial water permeability. (A; left) SLRM images of HBE cells before and 6 min after the addition of 300 mM mannitol to the basolateral perfusate. Dashed lines indicates fluid surface. (Middle) Corresponding intensity versus distance profiles shown at locations of dashed vertical lines. (Right) Time course of change in fluid height in HBE and T84 cells. Mean ± SEM of three cell inserts. (B; left) SLRM images before and 6 min after the addition of 300 mM mannitol to apical fluid in HBE cells. (Middle) Corresponding intensity versus distance profiles. (Right) Time course of change in fluid height. Mean ± SEM of three cell inserts.