Immunohistochemical localization of aquaporin 10 in the apical membranes of the human ileum: a potential pathway for luminal water and small solute absorption

A new member of the aquaporin family (AQP10) has recently been identified in the human small intestine by molecular cloning and in situ hybridization. Ribonuclease protection assay and northern blotting have demonstrated that AQP10 is expressed in the human duodenum and jejunum. However, the subcellular distribution of the AQP10 protein and its plasma membrane polarization have not yet been established. The objective of this study was to determine the distribution of the AQP10 protein in the human ileum by immunohistochemistry and western blotting using a polyclonal antibody raised against a unique 17-amino acid peptide derived from the human AQP10 sequence. The distribution of the AQP1 and AQP3 proteins was also studied by immunohistochemical staining using affinity-purified polyclonal antibodies. Results revealed that the AQP10 protein is preferentially targeted to the apical membrane domain of absorptive intestinal epithelial cells, whereas AQP3 is located in the basolateral membrane of the cells and AQP1 expression is restricted to the mucosal microvascular endothelia. The presence of AQP10 in the apical membrane of intestinal villi suggests that this protein may represent an entry pathway for water and small solutes from the lumen across to the mucosal side.