Colocalization of the apical Cl-/HCO3- exchanger PAT1 and gastric H-K-ATPase in stomach parietal cells (original) (raw)
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Identification of an apical Cl-/HCO3- exchanger in gastric surface mucous and duodenal villus cells
American journal of physiology. Gastrointestinal and liver physiology, 2003
The molecular identity of the apical HCO3(-)-secreting transporter in gastric mucous cells remains unknown despite its essential role in preventing injury and ulcer by gastric acid. Here we report the identification of a Cl-/HCO3- exchanger that is located on apical membranes of gastric surface epithelial cells. RT-PCR studies of mouse gastrointestinal tract mRNAs demonstrated that this transporter, known as anion exchanger isoform 4 (AE4), is expressed in both stomach and duodenum. Northern blot analysis of RNA from purified stomach epithelial cells indicated that AE4 is expressed at higher levels in mucous cells than in parietal cells. Immunoblotting experiments identified AE4 as a approximately 110- to 120-kDa protein in membranes from stomach epithelium and apical membranes from duodenum. Immunocytochemical staining demonstrated that AE4 is expressed in apical membranes of surface cells in both mouse and rabbit stomach and duodenum. Functional studies in oocytes indicated that A...
Identification of an apical Cl(-)/HCO3(-) exchanger in the small intestine
American journal of physiology. Gastrointestinal and liver physiology, 2002
HCO3(-) secretion is the most important defense mechanism against acid injury in the duodenum. However, the identity of the transporter(s) mediating apical HCO3(-) secretion in the duodenum remains unknown. A family of anion exchangers, which include downregulated in adenoma (DRA or SLC26A3), pendrin (PDS or SLC26A4), and the putative anion transporter (PAT1 or SLC26A6) has recently been identified. DRA and pendrin mediate Cl(-)/base exchange; however, the functional identity and distribution of PAT1 (SLC26A6) is not known. In these studies, we investigated the functional identity, tissue distribution, and membrane localization of PAT1. Expression studies in Xenopus oocytes demonstrated that PAT1 functions in Cl(-)/HCO3(-) exchange mode. Tissue distribution studies indicated that the expression of PAT1 is highly abundant in the small intestine but is low in the colon, a pattern opposite that of DRA. PAT1 was also abundantly detected in stomach and heart. Immunoblot analysis studies ...
Gastroenterology, 2004
Gastric parietal cells secrete acid into the lumen of the stomach. They express a proton pump, the gastric H(+)/K(+) ATPase, the activity of which is tightly regulated. The H(+)/K(+) ATPase traffics between an intracytoplasmic compartment (tubulovesicles) in quiescent parietal cells and the apical plasma membrane in activated cells. These trafficking events are considered to contribute to the control of acid secretion by modulating access to apical K(+) and Cl(-) conductances that are required for transmembrane H(+) ion transport by the H(+)/K(+) ATPase. Here, we have determined whether the control of acid secretion in vivo requires membrane trafficking of the H(+)/K(+) ATPase. We developed mice that only express an H(+)/K(+) ATPase beta subunit in which a putative tyrosine-based endocytosis motif in the cytoplasmic tail is mutated. Location of the H(+)/K(+) ATPase and parietal cell ultrastructure and gastric acid secretion were then examined. Parietal cells of these mice lacked a t...
Identification of a basolateral Cl-/HCO3- exchanger specific to gastric parietal cells
Gastroenterology, 2003
The basolateral Cl(-)/HCO(3)(-) exchanger in parietal cells plays an essential role in gastric acid secretion mediated via the apical gastric H(+)-K(+)-ATPase. Here, we report the identification of a new Cl(-)/HCO(3)(-) exchanger, which shows exclusive expression in mouse stomach and kidney, with expression in the stomach limited to the basolateral membrane of gastric parietal cells. Tissue distribution studies by RT-PCR and Northern hybridizations demonstrated the exclusive expression of this transporter, also known as SLC26A7, to stomach and kidney, with the stomach expression significantly more abundant. No expression was detected in the intestine. Cellular distribution studies by RT-PCR and Northern hybridizations demonstrated predominant localization of SLC26A7 in gastric parietal cells. Immunofluorescence labeling localized this exchanger exclusively to the basolateral membrane of gastric parietal cells, and functional studies in oocytes indicated that SLC26A7 is a DIDS-sensitive Cl(-)/HCO(3)(-) exchanger that is active in both acidic and alkaline pH(i). On the basis of its unique expression pattern and function, we propose that SLC26A7 is a basolateral Cl(-)/HCO(3)(-) exchanger in gastric parietal cells and plays a major role in gastric acid secretion.
Cell and Tissue Research, 2002
Ion transporters play a central role in gastric acid secretion. To determine whether some of these transporters are necessary for the normal ultrastructure of secretory membranes in gastric parietal cells, mice lacking transporters for H + , K + , Cl -, and Na + were examined for alterations in volume density (Vd) of basolateral, apical, tubulovesicular and canalicular membranes, microvillar dimensions, membrane flexibility, and ultrastructure. In mice lacking Na + /H + exchanger 1 (NHE1) or the Na + -K + -2Clcotransporter (NKCC1), the ultrastructure and Vd of secretory membranes and the secretory canalicular to tubulovesicular membrane ratio (SC/TV), a morphological correlate of secretory activity, were similar to those of wild-type mice. In mice lacking Na + /H + exchanger 2 (NHE2) or gastric H + , K + -ATPase αor β-subunits, the SC/TV ratio and Vd of secretory membranes were decreased, though canaliculi were often dilated. In H + , K + -ATPase-deficient parietal cells, canalicular folds were decreased, normally abundant tubulovesicles were replaced with a few rigid round vesicles, and microvilli were sparse, stiff and short, in contrast to the long and flexible microvilli in wild-type cells. In addition, microvilli of the H + , K + -ATPase-deficient parietal cells had centrally bundled F-actin filaments, unlike the microvilli of wild-type cells, in which actin filaments were peripherally positioned concentric to the plasmalemma. Data showed that the absence of H + , K + -ATPase produced fundamental changes in parietal cell membrane ultrastructure, suggesting that the pump provides an essential link between the membranes and F-actin, critical to the gross architecture and suppleness of the secretory membranes.
Acta Physiologica, 2011
Aims-The apical membrane anion exchanger Pat-1 is expressed at significant levels in the lower villus epithelium of murine duodenum. However, previous studies of Cl − /HCO 3 − exchange in the lower villus have failed to demonstrate Pat-1 function. Those studies routinely included luminal glucose which induces Na +-coupled glucose transport and acidifies the villus epithelium. Since Pat-1 has been proposed to be an electrogenic 1Cl − /2HCO 3 − exchanger, membrane depolarization or cell acidification during glucose transport may obscure Pat-1 activity. Therefore, we investigated the effects of luminal glucose on Cl − IN /HCO 3 − OUT exchange activity in the lower villus epithelium. Methods-Cl − IN /HCO 3 − OUT exchange of villus epithelium in duodenal mucosa from Pat-1 knockout (KO), Slc26a3 (Dra) KO, cystic fibrosis transmembrane conductance regulator (Cftr) KO and wild-type (WT) littermate mice was measured using the pH-sensitive dye BCECF. Shortcircuit current (I sc) was measured in Ussing chambers. Results-During glucose absorption, Cl − IN /HCO 3 − OUT exchange in the lower villus epithelium was abolished in the Dra KO and unaffected in the Pat-1 KO relative to WT. However, during electroneutral mannose absorption or electrogenic α-D-methyl glucoside absorption, Cl − IN / HCO 3 − OUT exchange was reduced in both Pat-1 KO and Dra KO villi. Exposure to high [K + ] abolished Cl − IN /HCO 3 − OUT exchange in the Dra KO but not the Dra/Cftr double KO epithelium, suggesting that Pat-1 activity is little affected by membrane depolarization except in the presence of Cftr. Conclusions-The metabolic and electrogenic activity of glucose transport obscures Cl − IN / HCO 3 − OUT exchange activity of Pat-1 in the lower villus. The inhibitory effects of membrane depolarization on Pat-1 Cl − IN /HCO 3 − OUT exchange may require concurrent membrane association with Cftr.
Proceedings of the National Academy of Sciences, 2008
Slc26a9 is a recently identified anion transporter that is abundantly expressed in gastric epithelial cells. To study its role in stomach physiology, gene targeting was used to prepare mice lacking Slc26a9. Homozygous mutant (Slc26a9 ؊/؊ ) mice appeared healthy and displayed normal growth. Slc26a9 deletion resulted in the loss of gastric acid secretion and a moderate reduction in the number of parietal cells in mutant mice at 5 weeks of age. Immunofluorescence labeling detected the H-K-ATPase exclusively on the apical pole of gastric parietal cells in Slc26a9 ؊/؊ mice, in contrast to the predominant cytoplasmic localization in Slc26a9 ؉/؉ mice.
Regulation of Cl/HCO3 exchange in gastric parietal cells
Cell Regulation, 1991
Microspectrofluorimetry of the fluorescent indicators 2',7'-bis-(2-carboxyethyl)-5(and-6)carboxyfluorescein and 6-methoxy-N-(3-sulfopropyl)-quinolinium was used to measure intracellular pH (pHi), intracellular Cl (Cli), and transmembrane fluxes of HCO3 and Cl in single parietal cells (PC) in isolated rabbit gastric glands incubated in HCO3/CO2-buffered solutions. Steady-state pHi was 7.2 in both resting (50 microM cimetidine) and stimulated (100 microM histamine) PCs. Transmembrane anion (HCO3 or Cl) flux rates during Cl removal from or readdition to the perfusate were the same in resting and stimulated PCs. These rates increased at alkaline pHi, though this pHi dependence was small in the physiological range. Maximum velocity (Vmax) for Cl influx or HCO3 efflux was 80-110 mM/min at pHi 7.6-7.8, and the Km for extracellular concentrations of Cl (Clo) was 25 mM; in the physiological range (pHi 7.1-7.3), Vmax for anion fluxes was approximately 50 mM/min. Steady-state Cli in th...