Expression and immunolocalization of AQP6 in intercalated cells of the ratkidney collecting duct

The expression and localization of AQP6 were examined in rat kidneys. In th e kidney compartments, the expression was more intense in the outer medulla than in the cortex or inner medulla, and was negative in the glomerulus. D uring development, the AQP6 mRNA expression in the kidney was not detected in the fetus, but was recognized at birth, increase gradually by 4 weeks of age, and was unchanged thereafter. In situ hybridization demonstrated sign ificant signals for AQP6 mRNA along the outer and inner medullary collectin g ducts. Since the localization of the AQP6 mRNA-expressing cells was compa rable to that of immunoreactive H+ ATPase-bearing cells in the collecting d uct, they were identified as intercalated cells. No AQP6 mRNA signals were recognizable in other cells in the kidneys, including glomerular cells. No glomerular expression of AQP6 mRNA was confirmed by RT-PCR using total RNA extracted from the glomeruli. Immunohistochemistry using an antibody raised against recombinant rat AQP6 protein could localize the immunoreactivity i n a population of collecting duct cells. Serial section observations indica ted that the AQP6-immunoreactive cells corresponded to H-ATPase bearing int ercalated cells.