Chloride transport in rabbit esophageal epithelial cells

Abstract

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[Formula: see text]), 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[Formula: see text] 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[Formula: see text] of 6.5 ± 0.9 mM. The depolarization and the rate of decrease of a[Formula: see text] were inhibited by ∼60% in the presence of the Cl−-channel blocker flufenamate. Serosal bumetanide significantly decreased the rate of change of a[Formula: see text] on removal and readdition of serosal Cl−. When a luminal cell was impaled, V mC was −65 ± 3.6 mV and a[Formula: see text] was 16.3 ± 2.2 mM. Removal of luminal Cl− depolarized V mC and decreased a[Formula: see text] by only 2.5 ± 0.9 mM. Subsequent removal of Cl− from the serosal bath decreased a[Formula: see text]in the luminal cell by an additional 6.4 ± 1.0 mM. A plot of V mBL measurements vs. log a[Formula: see text]/log a[Formula: see text] (a[Formula: see text] 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[Formula: see text]/a[Formula: see text]]. In contrast, V mC correlated very poorly with log a[Formula: see text]/a[Formula: see text] ( S = 18.9 mV/decade of change in a[Formula: see text]/a[Formula: see text]). These results indicate that 1) in rabbit EEC, a[Formula: see text] 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−.