Basolateral localization of anion exchanger 2 (AE2) and actin in acid-secreting (parietal) cells of the human stomach

Abstract

Basolateral uptake of chloride by the HCl-secreting parietal cells of the gastric (oxyntic) glands is most likely mediated by a HCO3-/Cl- anion exchange mechanism. Circumstantial evidence indicates that in rodents the anion exchange proceeds through an anion exchanger 2(AE2)-like membrane protein. In the present study, we raised antibodies against a bacterial fusion protein expressing a approximately 26-kDa portion of the human AE2 sequence. These antibodies were used to identify and localize AE2 in the human stomach. Here we report that the mucosa of the human stomach expresses an approximately 160-kDa immunoreactive form of AE2 containing the AE2-specific exoplasmic domain (Z-loop) as identified by polymerase chain reaction. Immunostaining specific for AE2 was restricted to the basolateral membrane domain of parietal cells and was also detected in small epithelial cells localized in the glandular isthmus region. The latter cells most likely represent pre-parietal cells. Parietal cells were identified by simultaneous and sequential labelling with antibodies against the gastric H+,K(+)-ATPase and actin, respectively. Both actin and the H+,K(+)-ATPase were localized along the apical membrane of parietal cells and the membrane of their secretory intracellular canaliculi. In addition, actin was shown to be colocalized with AE2 along the basolateral cell surface. Discontinuous staining for AE2 coincided with infoldings of the basolateral plasma membrane labelled by the actin antibody. These observations indicate that AE2 might be placed at specialized (folded) microdomains of the basolateral cell surface by linkage to the actin-based cytoskeleton.

Inefficient Chronic Activation of Parietal Cells in Ae2−/− Mice

“…Na ϩ -independent electroneutral Cl Ϫ /HCO 3 Ϫ exchange seems to be particularly relevant for bulk transport because it both supplies Cl Ϫ influx for its apical secretion and extrudes HCO 3 Ϫ , so as to acidify the cytosol and thereby allow apical proton secretion. [7][8][9][10][11] Previous studies have offered indirect evidence for a role of the basolateral Ae2 Cl Ϫ /HCO 3 Ϫ exchanger (Slc4a2) in this process, [12][13][14] although another basolateral Cl Ϫ /HCO 3 Ϫ exchanger, Slc26a7, has been identified in parietal cells, and a major role for this exchanger in gastric secretion was postulated. 15 However, mice with disruption of the Ae2 gene were recently reported to have a stomach content with neutral pH on stimulation with histamine, suggesting that gastric acid secretion entirely depends on Ae2 function.…”

In situ detection of AE2 anion-exchanger mRNA in the human liver

“…Recently, the molecular cloning of the human AE2 gene has been reported (Medina et al 1997). Expression of the AE2 gene (detected by Northern blotting, immunoblotting, or immunocytochemistry) has been reported in a variety of mammalian organs, such as choroid plexus, stomach, ileum, kidney, testis, cochlea, salivary gland, and liver (Alper et al 1988;Kudrycki et al 1990;Lindsey et al 1990;Chow et al 1992;Parkkila et al 1993;Jons et al 1994;Brosius et al 1995;Negrini et al 1995;Vµzquez et al 1995), in some of which the expressed protein might have a role in hydroionic fluxes into secretions. AE3 and AE3 isoforms appear to be expressed mainly in excitable tissues of the nervous system and in cardiac muscle Kudrycki et al 1990;Linn et al 1992Linn et al , 1995Yannoukakos et al 1994).…”

Identification of Residues Lining the Translocation Pore of Human AE1, Plasma Membrane Anion Exchange Protein

“…AE1 is a member of a multigene family (3); AE2 is most broadly expressed in tissues such as gastric parietal cells (4) and choroid plexus (5); AE3 is expressed in excitable tissues: heart (6), brain (7), and retina (8). All of the anion exchangers have a two-domain structure: a 55-kDa membrane domain responsible for anion exchange and a 43-77-kDa cytoplasmic domain involved in cytoskeletal interactions.…”