Highly polarized expression of carbohydrate‐binding protein p33/41 (annexin IV) on the apical plasma membrane of epithelial cells in renal proximal tubules

Abstract

p33/41 is a Ca(2+)-dependent carbohydrate-binding protein and is identical to annexin IV, a member of the annexin protein family. The localization of p33/41 in bovine kidney specimens was investigated immunohistochemically by use of specific polyclonal antibodies. The most interesting finding on immunostaining was that p33/41 was highly concentrated in the apical plasma membrane of the epithelial cells in the proximal tubules contrary to the distribution throughout the cytoplasm in the papillary ducts and papilla epithelium. The enrichment of p33/41 in the apical membrane was confirmed by immunoblotting of the brush border membrane fraction prepared from a kidney homogenate. Sequential extraction with EDTA and Triton X-100, and a partition experiment with Triton X-114 revealed that most p33/41 associates with the renal brush border membrane in a Ca(2+)-independent manner and is integrated into the membrane like intrinsic membrane proteins.