title: Bicarbonate and chloride secretion in Calu-3 human airway epithelial cells.
abstract: Serous cells are the predominant site of cystic fibrosis transmembrane conductance regulator expression in the airways, and they make a significant contribution to the volume, composition, and consistency of the submucosal gland secretions. We have employed the human airway serous cell line Calu-3 as a model system to investigate the mechanisms of serous cell anion secretion. Forskolin-stimulated Calu-3 cells secrete HCO-3 by a Cl-offdependent, serosal Na+-dependent, serosal bumetanide-insensitive, and serosal 4,4'-dinitrostilben-2,2'-disulfonic acid (DNDS)-sensitive, electrogenic mechanism as judged by transepithelial currents, isotopic fluxes, and the results of ion substitution, pharmacology, and pH studies. Similar studies revealed that stimulation of Calu-3 cells with 1-ethyl-2-benzimidazolinone (1-EBIO), an activator of basolateral membrane Ca2+-activated K+ channels, reduced HCO-3 secretion and caused the secretion of Cl- by a bumetanide-sensitive, electrogenic mechanism. Nystatin permeabilization of Calu-3 monolayers demonstrated 1-EBIO activated a charybdotoxin- and clotrimazole- inhibited basolateral membrane K+ current. Patch-clamp studies confirmed the presence of an intermediate conductance inwardly rectified K+ channel with this pharmacological profile. We propose that hyperpolarization of the basolateral membrane voltage elicits a switch from HCO-3 secretion to Cl- secretion because the uptake of HCO-3 across the basolateral membrane is mediated by a 4,4 '-dinitrostilben-2,2'-disulfonic acid (DNDS)-sensitive Na+:HCO-3 cotransporter. Since the stoichiometry reported for Na+:HCO-3 cotransport is 1:2 or 1:3, hyperpolarization of the basolateral membrane potential by 1-EBIO would inhibit HCO-3 entry and favor the secretion of Cl-. Therefore, differential regulation of the basolateral membrane K+ conductance by secretory agonists could provide a means of stimulating HCO-3 and Cl- secretion. In this context, cystic fibrosis transmembrane conductance regulator could serve as both a HCO-3 and a Cl- channel, mediating the apical membrane exit of either anion depending on basolateral membrane anion entry mechanisms and the driving forces that prevail. If these results with Calu-3 cells accurately reflect the transport properties of native submucosal gland serous cells, then HCO-3 secretion in the human airways warrants greater attention.
authors.affiliation: Department of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA. dd2+@pitt.edu
authors.forename: D C
authors.initials: DC
authors.lastname: Devor
authors.forename: A K
authors.initials: AK
authors.lastname: Singh
authors.forename: L C
authors.initials: LC
authors.lastname: Lambert
authors.forename: A
authors.initials: A
authors.lastname: DeLuca
authors.forename: R A
authors.initials: RA
authors.lastname: Frizzell
authors.forename: R J
authors.initials: RJ
authors.lastname: Bridges
mesh_terms: D001562:Benzimidazoles / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004594:Electrophysiology; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D013267:Stilbenes / Q000494:pharmacology
chemical_list: D001562:Benzimidazoles; D001639:Bicarbonates; D002120:Calcium Channel Agonists; D002712:Chlorides; D004232:Diuretics; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013267:Stilbenes; D002034:Bumetanide; D005576:Colforsin; C022306:4,4'-dinitro-2,2'-stilbenedisulfonic acid; C102635:1-ethyl-2-benzimidazolinone