Water permeability in different epithelial barriers

The water permeability properties of a series of epithelial barriers (the toad urinary bladder [TUB], the rat caecum [RC], the distal human colon [DHC], and the human amnion [HA] were studied in different experimental conditions. Three parameters were simultaneously determined: the water permeability coefficient in the presence of a transepithelial hydrostatic gradient (Phydr); the water permeability coefficient in the presence of an osmotic gradient (Posm); and the transepithelial potential difference (dV). All experiments were performed with the same experimental device, allowing comparison of the permeability properties of the barriers tested. The results obtained were: (1) TUB (N = 8): Phydr = 0.079 +/- 0.008 cm/s; Posm = 0.0004 +/- 0.0002 cm/s; dV = 31 +/- 5 mV; (2) TUB after ADH (N = 8): Phydr = 0.093 +/- 0.012 cm/s; Posm = 0.0065 +/- 0.0011 cm/s; dV = 52 +/- 8; (3) RC (N = 10): Phydr = 0.18 +/- 0.02 cm/s; Posm = 0.0019 +/- 0.0004 cm/s; dV = 3.9 +/- 0.1 mV; (4) RC adapted to a high K diet (N = 10): Phydr = 0.21 +/- 0.02 cm/s; Posm = 0.0018 +/- 0.0006 cm/s; dV = 4.5 +/- 0.5 mV; (5) DHC (N = 6): Phydr = 0.22 +/- 0.03 cm/s; Posm = 0.002 +/- 0.05 cm/s; dV = 15 +/- 3 mV; (6) HA (N = 10): Phydr = 0.32 +/- 0.05 cm/s; Posm = 0.0154 +/- 0.0015; dV = 0. The results show a good correlation between Phydr and dV, but not between dV and Posm or between Posm and Phydr.