BASOLATERAL LOCALIZATION OF ANION-EXCHANGER-2 (AE2) AND ACTIN IN ACID-SECRETING (PARIETAL) CELLS OF THE HUMAN STOMACH

Basolateral uptake of chloride by the HCl-secreting parietal cells of the gastric (oxyntic) glands is most likely mediated by a HCO3-/Cl- an ion exchange mechanism. Circumstantial evidence indicates that in rode nts 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 similar to 26-kDa portion of t he human AE2 sequence. These antibodies were used to identify and loca lize AE2 in the human stomach. Here we report that the mucosa of the h uman stomach expresses an similar to 160kDa immunoreactive form of AE2 containing the AE2-specific exoplasmic domain (Z-loop) as identified by polymerase chain reaction. Immunostaining specific for AE2 was rest ricted to the basolateral membrane domain of parietal cells and was al so detected in small epithelial cells localized in the glandular isthm us region. The latter cells most likely represent pre-parietal cells. Parietal cells were identified by simultaneous and sequential labellin g with antibodies against the gastric H+,K+-ATPase and actin, respecti vely. Both actin and the H+,K+-ATPase were localized along the apical membrane of parietal cells and the membrane of their secretory intrace llular canaliculi. In addition, actin was shown to be colocalized with AE2 along the basolateral cell surface. Discontinuous staining for AE 2 coincided with infoldings of the basolateral plasma membrane labelle d by the actin anti body. These observations indicate that AE2 might b e placed at specialized (folded) microdomains of the basolateral cell surface by linkage to the actin-based cytoskeleton.