Chloride transport in rabbit esophageal epithelial cells.
We investigated Cl(-) transport pathways in the apical and basolateral membranes of rabbit esophageal epithelial cells (EEC) using conventional and ion-selective microelectrodes. Intact sections of esophageal epithelium were mounted serosal or luminal side up in a modified Ussing chamber, where transepithelial potential difference and transepithelial resistance could be determined. Microelectrodes were used to measure intracellular Cl(-) activity (a), basolateral or apical membrane potentials (V(mBL) or V(mC)), and the voltage divider ratio. When a basal cell was impaled, V(mBL) was -73 +/- 4.3 mV and a(i)(Cl) was 16.4 +/- 2.1 mM, which were similar in presence or absence of bicarbonate. Removal of serosal Cl(-) caused a transient depolarization of V(mBL) and a decrease in a(i)(Cl) of 6.5 +/- 0.9 mM. The depolarization and the rate of decrease of a(i)(Cl) were inhibited by approximately 60% in the presence of the Cl(-)-channel blocker flufenamate. Serosal bumetanide significantly decreased the rate of change of a(i)(Cl) on removal and readdition of serosal Cl(-). When a luminal cell was impaled, V(mC) was -65 +/- 3.6 mV and a was 16.3 +/- 2.2 mM. Removal of luminal Cl(-) depolarized V(mC) and decreased a by only 2.5 +/- 0.9 mM. Subsequent removal of Cl(-) from the serosal bath decreased a(i)(Cl) in the luminal cell by an additional 6.4 +/- 1.0 mM. A plot of V(mBL) measurements vs. log a(i)(Cl)/log a(o)(Cl) (a(o)(Cl) is the activity of Cl(-) in a luminal or serosal bath) yielded a straight line [slope (S) = 67.8 mV/decade of change in a(i)(Cl)/a(o)(Cl)]. In contrast, V(mC) correlated very poorly with log a/a (S = 18.9 mV/decade of change in a/a). These results indicate that 1) in rabbit EEC, a(i)(Cl) is higher than equilibrium across apical and basolateral membranes, and this process is independent of bicarbonate; 2) the basolateral cell membrane possesses a conductive Cl(-) pathway sensitive to flufenamate; and 3) the apical membrane has limited permeability to Cl(-), which is consistent with the limited capacity for transepithelial Cl(-) transport. Transport of Cl(-) at the basolateral membrane is likely the dominant pathway for regulation of intracellular Cl(-).
Abdulnour-Nakhoul
Solange
S
Department of Medicine, Tulane University School of Medicine, and Veterans Administration Medical Center, New Orleans, Louisiana 70112-2699, USA. solange@tulane.edu
Nakhoul
Nazih L
NL
Caymaz-Bor
Canan
C
Orlando
Roy C
RC
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000085:Acetates / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D001693:Biological Transport, Active; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D004553:Electric Conductivity; D017097:Electric Impedance; D004847:Epithelial Cells / Q000378:metabolism; D004947:Esophagus / Q000378:metabolism*; D005439:Flufenamic Acid / Q000494:pharmacology; D007192:Indenes / Q000494:pharmacology; D008564:Membrane Potentials; D008839:Microelectrodes; D011817:Rabbits
D000085:Acetates; D001639:Bicarbonates; D002712:Chlorides; D007192:Indenes; D002034:Bumetanide; C095651:((2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy)acetic acid; D002245:Carbon Dioxide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D005439:Flufenamic Acid; D000242:Cyclic AMP; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium