Expression of Aquaporin-6 in Intercalated Cell subtypes in Rat and Mouse Kidney

Hwang, Jin Sun; Kim, Young Hee; Park, Eun Young; Kim, Wan Young; Kim, Jin

Abstract

Aquaporin-6 (AQP6) is a water channel protein located in intracellular vesicles of the proximal tubules and in intercalated cells (ICs) in the collecting duct (CD) of the rat kidney. The function of AQP6 is unknown. However, it colocalizes with vacuolar H+-ATPase in type-A ICs, indicating that it may be important for the function of proton pumps in these cells. The aims of this study were to compare the expression of AQP6 between rat and mouse kidneys, and to establish which types of IC express AQP6. Kidneys of adult male rats and mice were processed for immunohistochemistry using antibodies against AQP6, H+-ATPase, and anion exchanger 1 (AE1). AQP6 was expressed in the S1, S2, and S3 segments of the proximal tubule and in ICs of the CD and connecting tubule (CNT) in both rats and mice. In the rat proximal tubule, AQP6 immunoreactivity was present in intracellular vesicles, whereas in the mouse proximal tubule it was present in the brush border as well as in intracellular vesicles. Triple immunostaining for AQP6, AE1, and H+-ATPase revealed that AQP6 was expressed only in type-A ICs in the CDs and CNTs of both rats and mice, and that the staining was diffuse throughout. There was no AQP6 labeling of type-B ICs, non-A-non-B ICs, or principal cells. The functional significance of the expression of AQP6 in proximal tubule cells and type-A ICs remains to be established. We propose that AQP6 is involved in the retrieval and maintenance of H+-ATPasecontaining vesicles in acid-secreting epithelial cells in the kidney.