title: Contribution of active Na+ and Cl- fluxes to net ion transport by alveolar epithelium.
abstract: Changes in bioelectric properties of alveolar epithelial cell monolayers due to pharmacological agents such as beta-agonists, amiloride and ouabain have recently been reported. In order to determine specifically which ionic species contribute to these changes, fluxes of Na+ and Cl- across primary cultured monolayers of rat type II pneumocytes were directly measured. Monolayers were mounted in modified flux chambers and short-circuited. Unidirectional fluxes of 22Na (or 36Cl) and [14C]-mannitol were measured simultaneously. Experimental maneuvers included apical (A) exposure to 10 microM amiloride, basolateral (B) exposure to 1 mM ouabain, or basolateral exposure to 20 microM terbutaline. Results show that baseline monolayers actively reabsorb Na+ (about 0.14 micro Eq.cm-2.h-1) from the apical fluid, while mannitol and Cl- appear to traverse the alveolar epithelium passively. Active Na+ reabsorption was abolished by amiloride or ouabain, while Cl- and mannitol fluxes were unaffected. Terbutaline, on the other hand, markedly increased net absorption of Na+ and caused active transport of Cl- in the A to B direction. Passive mannitol flow was somewhat increased with terbutaline. These data indicate that active Na+ reabsorption across alveolar epithelial monolayers is dependent on intact Na+,K(+)-ATPase activity and cell Na+ entry (probably via Na+ channels), and can be stimulated by beta-agonists. Beta-agonists also cause active reabsorption of Cl- (passive under other conditions).
authors.affiliation: Will Rogers Institute, Department of Medicine, University of Southern California, Los Angeles 90033.
authors.forename: K J
authors.initials: KJ
authors.lastname: Kim
authors.forename: J M
authors.initials: JM
authors.lastname: Cheek
authors.forename: E D
authors.initials: ED
authors.lastname: Crandall
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D007700:Kinetics; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
chemical_list: D002712:Chlorides; D010042:Ouabain; D000584:Amiloride; D012964:Sodium