Expression of Aquaporins in the Rat Choroid Plexus

Aquaporins (AQPs) are water channels that play a key role in water transport in many epithelia. Recent studies have shown that AQP1, located in the apical membrane of choroid plexus cells, has an important role in cerebrospinal fluid (CSF) production. However, the mechanism of water transport through the basolateral membrane of choroid plexus (CP) cells is yet to be determined. In this study, the expression and localization of AQP1, AQP4 and AQP5 in the rat lateral ventricle CP were investigated by immunocytochemistry, western analysis and flowcytometry. Choroidal epithelial cells of the lateral ventricle in Wistar rats were isolated and grown in Dulbecco's Modified Eagle's medium (DMEM) supplement, which was refreshed every two days. After five days, the expression patterns of AQP1, AQP4 and AQP5 were determined by immunoblotting, immuncytochemistry and flowcytometry. The immunocytochemistry data revealed the expression of AQP1 and AQP4 in the membrane and the cytoplasmof AP cells, respectively. Through western analysis, the AQP1 antibody detected two bands of approximately 27 and 32 kDa. A single peptide of 29 kDa was recognized by the AQP4 antibody. Quantitative flowcytometry revealed CP cells exhibiting a high level of AQP1 and AQP4 proteins (95.39% and 92.21%, respectively). According to immunocytochemistry, AQP5 is weakly expressed in the cytoplasm of CP cells. Anti-AQP5 antibody recognized a pale band of approximately28 kDa by western analysis. These observations suggested that AQP4 may have an important role in CSF secretion; however, expression of AQP4 or AQP5 was not detected in the cell membrane. Thus, how water crosses the basolateral membrane of CP cells remains to be determined.