Bidirectional Transepithelial Water Transport: Measurement and Governing Mechanisms

• Published in: Biophysical journal Vol. 76; no. 2; pp. 869 - 877
• Main Authors: Phillips, Jonathan E., Wong, Lid B., Yeates, Donovan B.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.1999; Biophysical Society
• Subjects: Animals; Biological Transport; Biology; Cell Membrane Permeability - physiology; Deuterium Oxide - metabolism; Diffusion; Electrophysiology; Epithelial Cells - metabolism; Epithelial Cells - physiology; Fluorescence; Ion Transport - physiology; Membranes; Naphthalenes - metabolism; Photons; Sheep; Sodium; Trachea - physiology; Water; Water - metabolism
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(99)77250-4

In the search for the mechanisms whereby water is transported across biological membranes, we hypothesized that in the airways, the hydration of the periciliary fluid layer is regulated by luminal-to-basolateral water transport coupled to active transepithelial sodium transport. The luminal-to-basolateral ( J W L→B) and the basolateral-to-luminal ( J W B→L) transepithelial water fluxes across ovine tracheal epithelia were measured simultaneously. The J W L→B (6.1 μl/min/cm 2) was larger than J W B→L (4.5 μl/min/cm 2, p < 0.05, n = 30). The corresponding water diffusional permeabilities were P d L→B = 1.0 × 10 −4 cm/s and P d B→L = 7.5 × 10 −5 cm/s. The activation energy ( E a) of J W L→B (11.6 kcal/mol) was larger than the E a of J W B→L (6.5 kcal/mol, p < 0.05, n = 5). Acetylstrophanthidin (100 μM basolateral) reduced J W L→B from 6.1 to 4.4 μl/min/cm 2 ( p < 0.05, n = 5) and abolished the PD. Amiloride (10 μM luminal) reduced J W L→B from 5.7 to 3.7 μl/min/cm 2 ( p < 0.05, n = 5) and reduced PD by 44%. Neither of these agents significantly changed J W B→L. These data indicate that in tracheal epithelia under homeostatic conditions, J W B→L was dominated by diffusion ( E a = 4.6 kcal/mol), whereas ∼30% of J W L→B was coupled to the active Na +,K +-ATPase pump ( E a = 27 kcal/mol).