In situ localization of anion exchanger-2 in the human kidney

Naf-independent anion exchangers (AE) are a family of membrane carriers tha t mediate the electroneutral exchange of Cl- for HCO3- ions across plasma m embranes. They are involved in intracellular pH and cell volume regulation as well as in transepithelial acid-base transport. While anion exchanger-1 (AE1) has been localized previously in the human kidney, thus far there has been no definite report on anion exchanger-2 (AE2) in this human tissue. A ccordingly, immunohistochemistry was carried out on surgical specimens of t he human kidney (fixed in formalin and embedded in paraffin), using a speci fic AE2 monoclonal antibody. Strong immunostaining was observed at the baso lateral membrane of cells of thick ascending limbs and distal convoluted tu bules, colocalizing with the basal membranous labyrinth of cellular interdi gitations, typical of these segments. In fact, AE2 staining was attenuated at the macula densa, where basal infoldings are scarce. Additionally, in si tu hybridization experiments on formalin-fixed tissue demonstrated the pres ence of AE2 mRNA in the same segments of the distal nephron. On the other h and, control immunohistochemistry with a monoclonal antibody against AE1 ga ve the expected immunoreactivity at the basal pole of the type A intercalat ed cells of connecting tubules and cortical collecting ducts, and in erythr ocytes. Our results indicate that, depending on the nephron segment and cor responding cell types, AE1 and AE2 proteins are differentially involved in the Na+-independent exchange of Cl- for HCO3- at the basolateral membrane o f polarized kidney epithelial cells.