title: Active 22Na+ transport by the intact lung during early postnatal life.
abstract: The lung relies upon epithelial active transport of Na+ to aid in the clearance of fluid from its air spaces. Because it is unknown whether the rate of active Na+ transport by the distal lung epithelium varies during early postnatal age, we performed studies in young guinea pigs (7 and 30 days after birth). We used a single pass isolated perfused lung model in which a Krebs Ringer bicarbonate solution containing 22Na+, [14C]sucrose, and FITC-dextran was placed into the air spaces of the lungs, and apparent permeability-surface area (PS) products were calculated after determining the changes in lung weight and the concentrations of the isotopes in the vascular effluent. The PS product for 22Na+, but not [14C]sucrose, decreased significantly at both ages when amiloride was infused (final concentration of 10(-4) M). Amiloride also decreased the rate of fluid clearance, as assessed by changes in organ weight, at both ages. Although the absolute rate of amiloride-sensitive 22Na+ transport increased with age, morphometric measurement of the alveolar region demonstrated that the rate of amiloride-sensitive 22Na+ transport per unit alveolar surface area was similar. These data indicate that although the guinea pig lung undergoes significant growth shortly after birth, the rate of amiloride-sensitive active Na+ transport per unit surface area remains constant. Since a component of weight loss was insensitive to amiloride, these in vivo studies suggest that the amiloride-insensitive Na+ transport pathways previously identified in cultured lung epithelium exist in the intact lung.
authors.affiliation: Department of Paediatrics, Hospital for Sick Children, University of Toronto, ON, Canada.
authors.forename: H M
authors.initials: HM
authors.lastname: O'Brodovich
authors.forename: B
authors.initials: B
authors.lastname: Mullen
authors.forename: V L
authors.initials: VL
authors.lastname: Hannam
authors.forename: B E
authors.initials: BE
authors.lastname: Goodman
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D004848:Epithelium / Q000254:growth & development / Q000378:metabolism; D006168:Guinea Pigs; D017136:Ion Transport / Q000187:drug effects; D008168:Lung / Q000254:growth & development / Q000378:metabolism*; D011654:Pulmonary Edema / Q000378:metabolism; D012979:Sodium Radioisotopes / Q000378:metabolism*
chemical_list: D012979:Sodium Radioisotopes; D000584:Amiloride