SLC26A7 Can function as a chloride-loading mechanism in parietal cells

Abstract

To date three potential candidates for parietal cell basolateral Cl⁻ entry have been described: the highly 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS)-sensitive ${{\text{Cl}}^{{\text{ - }}} } \mathord{\left/ {\vphantom {{{\text{Cl}}^{{\text{ - }}} } {{\text{HCO}}_{{\text{3}}} ^{ - } }}} \right. \kern-\nulldelimiterspace} {{\text{HCO}}_{{\text{3}}} ^{ - } }$ exchanger AE2, the ${\text{HCO}}_{{\text{3}}} ^{ - }$ and lowly DIDS-sensitive SLC26A7 protein, and the Na⁺-2Cl⁻K⁺ cotransporter (NKCC1). In this study we investigate the contribution of these pathways to secretagogue stimulated acid secretion. Individually hand-dissected rat gastric glands were microfluorimetrically monitored for Cl⁻ influx and pH_i changes. Transporter activity was determined by varying ion content and through the use of pharmacological inhibitors. Expression of SLC26A7 in rat parietal cells was shown by immunohistochemistry and Western blot. SLC26A7 was inhibited by 5-Nitro-2-(3-phenylpropyl-amino)benzoic acid (NPPB) (100 μM) in the Xenopus laevis oocyte expression system. Cl⁻ influx in parietal cells was enhanced by histamine, depended partially on endogenous ${\text{HCO}}_{{\text{3}}} ^{ - }$ synthesis and completely on extracellular Na⁺. Removal and subsequent readdition of Cl⁻ revealed a low and a high DIDS-sensitive ${\text{HCO}}_{{\text{3}}} ^{ - }$ extrusion system contributing to Cl⁻ uptake. At acidic pH_i, however, H⁺ extrusion via the H⁺,K⁺-ATPase depending on Cl⁻ uptake was abolished only in the presence of 100 μM (NPPB) and at high (250 μM) DIDS concentration. There was no effect of the NKCC inhibitor bumetanide on stimulated H⁺ extrusion. These results would be compatible with SLC26A7 as a Cl⁻ uptake system under histamine stimulation.