Ammonia excretion in the renal collecting duct is critical in the regulation of the acid-base homeostasis. A novel family of ammonium transporter protein, Rh B Glycoprotein (RhBG) was recently identified in the mouse and rat kidney collecting duct. The purpose of this was to examine the ultrastructural localization of RhBG in the collecting duct. Rat kidneys were processed for light and electron microscope immunocytochemistry using anti-RhBG rabbit polyclonal antibody. Strong RhBG immunolabeling was observed in the basolateral plasma membrane of type A intercalated cells in the collecting duct. In contrast, RhBG labeling was very weak or negative in type B intercalated cells and principal cells. Transmission electron microscopy confirmed that RhBG immunostaining was located mainly in the basolateral plasma membrane and infoldings of type A intercalated cells, but very weak in type B cells. RhBG labeling was not observed in the apical plasma membrane both in type A and B cells. These results demonstrate that RhBG is a basolateral transporter in acid-secreting type A cells and may mediate ammonia excretion in the collecting duct.
Ammonia ; Ammonium Compounds* ; Animals ; B-Lymphocytes ; Cell Membrane ; Glycoproteins ; Homeostasis ; Humans ; Immunohistochemistry ; Kidney Tubules, Collecting* ; Kidney* ; Mice ; Microscopy, Electron, Transmission ; Rats*

Osteopontin (OPN) is a secretory protein that plays an important role in urinary stone formation. Hydration status is associated with the development of urolithiasis. This study was conducted to examine the effects of dehydration and hydration on OPN expression in the rat kidney. Animals were divided into three groups, control, dehydrated, and hydrated. Kidney tissues were processed for light and electron microscope immunocytochemistry, in situ hybridization, and immunoblot analysis. Dehydration induced a significant increase in OPN protein expression, whereas increased fluid intake induced a decrease in protein expression. Under control conditions, OPN protein and mRNA expression were only detected in the descending thin limb (DTL). Dehydration induced increased expression in the DTL and the development of detectable expression in the thick ascending limb (TAL). In contrast, OPN expression levels declined to less than the controls in the DTL after hydration, while no expression of either protein or mRNA was detectable in the TAL. Immunoelectron microscopy demonstrated that hydration status altered tubular ultrastructure and intracellular OPN expression in the Golgi apparatus and secretory cytoplasmic vesicles. These data confirm that changes in oral fluid intake can regulate renal tubular epithelial cell OPN expression.
Animals ; Control Groups ; Cytoplasmic Vesicles ; Dehydration ; Epithelial Cells ; Extremities ; Golgi Apparatus ; Immunohistochemistry ; In Situ Hybridization ; Kidney* ; Microscopy, Immunoelectron ; Osteopontin* ; Rats* ; RNA, Messenger ; Urinary Calculi ; Urolithiasis