Most basal I(SC) in Calu-3 human airway cells is bicarbonate-dependent Cl- secretion.
Serous cells secrete antibiotic-rich fluid, but secretion is impaired in cystic fibrosis. We are investigating Calu-3 cells as a serous cell model. Basal short-circuit current (I[SC]) in Calu-3 cells grown at air interface had a basal I(SC) approximately six times larger than submerged cultures (69 +/- 22 vs. 11 +/- 10 microA/cm2). Basal I(SC) in either condition was reduced only 7 +/- 5% by bumetanide and was unaffected by apical amiloride, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS), or calixarene but was reduced 77 +/- 18% by N-phenylanthranilic acid. Three transport mechanisms accounted for almost all basal I(SC). The largest component is HCO3(-)-dependent Cl- secretion. Replacement of Krebs-Henseleit solution with N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solution and changing gassing from 95% O2-5% CO2 to air reduced the basal I(SC) by 61 +/- 10%. Acetazolamide decreased basal I(SC) by 33 +/- 6%, whereas acetazolamide + basolateral DNDS eliminated 42-58% of the bumetanide-insensitive basal I(SC). Neither DNDS nor acetazolamide had any effect when applied in HCO3(-)-free solution. Apical phlorizin, a blocker of Na+-glucose cotransport, eliminated one-half of the remaining I(SC). Cl- replacement with gluconate eliminated all I(SC) except the phlorizin-sensitive component. Unlike basal I(SC), 80 +/- 24% of stimulated I(SC) was inhibited by bumetanide. Thus basal and stimulated secretions are mediated by different mechanisms.
Singh
M
M
Cystic Fibrosis Research Laboratory, Stanford University, California 94305-2130, USA.
Krouse
M
M
Moon
S
S
Wine
J J
JJ
D000584:Amiloride / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects; D002712:Chlorides / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D004553:Electric Conductivity; D006801:Humans; D008168:Lung / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013267:Stilbenes / Q000494:pharmacology; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D001639:Bicarbonates; D002712:Chlorides; D013267:Stilbenes; D062367:ortho-Aminobenzoates; D002034:Bumetanide; D000584:Amiloride; C001209:fenamic acid