title: Cation selective channel in fetal alveolar type II epithelium.
abstract: A cation selective channel was identified in the apical membrane of fetal rat (Wistar) alveolar type II epithelium using the patch clamp technique. The single channel conductance was 23 +/- 1.2 pS (n = 16) with symmetrical NaCl (140 mM) solution in the bath and pipette. The channel was highly permeable to Na+ and K+ (PNa/PK = 0.9) but essentially impermeant to chloride and gluconate. Membrane potential did not influence open state probability when measured in a high Ca2+ (1.5 mM) bath. The channel reversibly inactivated when the bath was exchanged with a Ca(2+)-free (less than 10(-9) M) solution. The Na+ channel blocker amiloride (10(-6) M) applied to the extracellular side of the membrane reduced P(open) relative to control patches; P(control) = 0.57 +/- 0.11 (n = 5), P(amiloride) = 0.09 +/- 0.07 (n = 4, p less than 0.01), however, amiloride did not significantly influence channel conductance (g); g(control) 19 +/- 0.9 pS (n = 5), 18 +/- 3.0 pS (n = 4). More than one current level was observed in 42% (16/38) of active patches; multiple current levels (ranging from 2 to 6) were of equal amplitude suggesting the presence of multiple channels or subconductance states. Channel activity was also evident in cell attached patches. Since monolayers of these cells absorb Na+ via an amiloride sensitive transport mechanism we speculate that this amiloride sensitive cation selective channel is a potential apical pathway for electrogenic Na+ transport in the alveolar region of the lung.
authors.affiliation: Respiratory Research Division, Hospital for Sick Children, Toronto, Canada.
authors.forename: B A
authors.initials: BA
authors.lastname: Orser
authors.forename: M
authors.initials: M
authors.lastname: Bertlik
authors.forename: L
authors.initials: L
authors.lastname: Fedorko
authors.forename: H
authors.initials: H
authors.lastname: O'Brodovich
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D004848:Epithelium / Q000378:metabolism; D005333:Fetus / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000196:embryology / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*
chemical_list: D015221:Potassium Channels; D015222:Sodium Channels; D000584:Amiloride