Immunolocalization and tissue-specific splicing of AE2 anion exchanger in mouse kidney

In this study, an epitope-unmasking technique was used to immunolocalize AE2 anion exchanger polypeptide to basolateral plasma membranes of tubular epithelial cells in mouse kidney. Kidney AE2 immunostaining in mouse kidney was less prominent than in rat, consistent with the relative levels of AE2 mRNA and polypeptide in these two species. Glomeruli showed faint but consistent AE2 immunostaining, whereas proximal tubules were generally unstained. Macula densa epithelial cells displayed bright AE2 immunostaining, and cortical thick limbs were stained at a lower intensity. AE2 immunostaining was weak or absent in type B intercalated cells and principal cells of the cortical collecting duct, but increased in intensity in principal cells of the inner stripe of the outer medulla. AE2 staining in medullary thick limbs was also of greater intensity than in cortical thick limbs. AE2 staining was strong and uniform in the epithelial cells of the inner medullary collecting duct, and in epithelial cells of the papillary surface, the ureter, and the urinary bladder. Extratubular and epithelial cells of the inner medulla also showed punctate intracellular AE2 staining in a Golgi-like distribution that, in contrast to cell surface staining, was sodium dodecyl sulfate-sensitive. Golgi localization of AE2 epitope was confirmed by immunoperoxidase electron microscopy. Reverse transcription-PCR analysis of mouse kidney RNA detected AE2a, AE2b, and an AE2c2 transcript, but an AE2c1 transcript was absent. Unlike in rat, the mouse AE2c2 mRNA splice variant encoded a polypeptide with a novel predicted N-terminal amino acid sequence.