title: Evidence for apical sodium channels in frog lung epithelial cells.
abstract: To reveal the mechanism of Na+ transport across Xenopus lung epithelium, we recorded short-circuit current (Isc), transepithelial resistance (Rt), and current noise spectra while the isolated lung tissues were mounted in an Ussing-type chamber. Mean values of Isc and Rt obtained while the tissue was bilaterally incubated with NaCl-Ringer solution were Isc = 11.57 +/- 1.19 microA.cm-2 and Rt = 0.82 +/- 0.07 k omega.cm2. Amiloride added to the mucosal (apical) side depressed Isc by 61 to 99%. Ouabain abolished Isc totally when added to the basolateral compartment. Adenosine 3',5'-cyclic monophosphate (cAMP), epinephrine, and a variety of other compounds did not alter Isc significantly. Transepithelial depolarization with serosal KCl solution reduced Isc to 6.22 +/- 1.37 microA.cm-2. Amiloride-sensitive current and the kinetics of amiloride interaction were not significantly affected by depolarization. Fluctuation analysis of Isc in the presence of amiloride revealed a Lorentzian component in the power density spectrum indicating apical Na+ channels. Assuming pseudo-first order kinetics, we calculated single channel currents (iNa) and channel density (M): iNa = 0.29 +/- 0.04 pA and M = 0.24 +/- 0.04 micron 2. Our results show that the route for Na+ transport through lung epithelial cells follows the classical Koefoed-Johnson-Ussing model for tight epithelia.
authors.affiliation: Institut für Veterinärphysiologie, Freie Universität Berlin, Federal Republic of Germany.
authors.forename: H
authors.initials: H
authors.lastname: Fischer
authors.forename: W
authors.initials: W
authors.lastname: Van Driessche
authors.forename: W
authors.initials: W
authors.lastname: Clauss
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D004848:Epithelium / Q000502:physiology / Q000648:ultrastructure; D005260:Female; D007700:Kinetics; D008168:Lung / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008854:Microscopy, Electron; D010042:Ouabain / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D002712:Chlorides; D015222:Sodium Channels; D010042:Ouabain; D011189:Potassium Chloride; D000584:Amiloride; D012964:Sodium