Na+ and Cl- transport across rabbit nonciliated bronchiolar epithelial (Clara) cells.
Radioisotopic flux measurements were performed on rabbit Clara cell epithelium cultured in serum-free hormone-supplemented medium to identify the major ion transport pathways in the cell type. Clara cells cultured in serum-free hormone-supplemented medium exhibit a large short-circuit current compared with cells maintained in serum-containing medium (45 microA/cm2 vs. 15 microA/cm2). The responses to amiloride and isoproterenol, however, are similar for cells grown in the two media. A net amiloride-sensitive movement of Na+ in the mucosal (M)-to-serosal (S) direction undershort- and open-circuit conditions is detected (1.48 and 0.67 mueq.h-1.cm-2, respectively). No statistically significant difference in the unidirectional fluxes of Cl- is apparent in the basal state, but a net flux of Cl- in the S-to-M direction is observed after exposure of the apical membrane to amiloride (0.93 mueq.h-1.cm-2). The partial ionic conductances for Na+ and Cl- estimated from the fluxes measured in the passive directions (JNaS----M, JClM----S) exceed the total tissue conductance by 20%. Ussing flux ratio analyses of Cl- movements at clamped potentials between -60 and +20 mV show that Cl- movements are not strictly through passive conductive pathways at negative potentials. The movement of Cl- can be modeled by passive diffusion combined with Cl- -Cl- exchange equal to 20% of total passive fluxes of Na+ and Cl-. These observations indicate that 1) Na+ absorption is the major active ion transport pathway across cultured Clara cells, 2) active Cl- secretion is minimal in the basal state, and 3) approximately 20% of the unidirectional Cl- fluxes occur via nonconductive pathways.
Van Scott
M R
MR
Department of Medicine, University of North Carolina, Chapel Hill 27599-7020.
Davis
C W
CW
Boucher
R C
RC
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
D002712:Chlorides; D000584:Amiloride; D012964:Sodium; D007545:Isoproterenol