title: Active Na+ transport across Xenopus lung alveolar epithelium.
abstract: Bioelectric properties and unidirectional ion fluxes of alveolar epithelium were studied by utilizing excised Xenopus lungs mounted in the flux chamber under short-circuited conditions. Results show that the alveolar epithelium generates a potential difference (PD) of 8 mV (lumen negative) with a tissue resistance (Rt) of 1000 ohm.cm2. The short-circuit current (Isc) is inhibitable by 80% with alveolar amiloride. Alveolar or pleural exposure of ouabain slowly decreases Isc to zero. Rt is slightly increased by either agent. Control tissues exhibit a greater unidirectional 22Na+ flux in the alveolar to pleural (A----P) direction than in the opposite (P----A) direction, indicating a net removal of Na+ from the alveolar fluid. Amiloride and ouabain both decrease the A----P Na+ flux to the level of the P----A flux, thereby abolishing net Na+ absorption. In contrast, unidirectional 36Cl fluxes are not different in either direction. Neither amiloride nor ouabain affected these 36Cl fluxes and tissue resistance appreciably, indicating that Cl- passively permeates the alveolar epithelium.
authors.affiliation: Department of Medicine, Cornell University Medical College, New York, NY 10021.
authors.forename: K J
authors.initials: KJ
authors.lastname: Kim
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002712:Chlorides / Q000493:pharmacokinetics; D004848:Epithelium; D005260:Female; D007477:Ions; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D010994:Pleura / Q000378:metabolism / Q000502:physiology; D011650:Pulmonary Alveoli / Q000378:metabolism* / Q000502:physiology; D012964:Sodium / Q000493:pharmacokinetics*; D014982:Xenopus laevis
chemical_list: D002712:Chlorides; D007477:Ions; D010042:Ouabain; D000584:Amiloride; D012964:Sodium