Localization of the ammonium transporter proteins RhBG and RhCG in mouse kidney

Ammonia is both produced and transported by renal epithelial cells, and it regulates renal ion transport. Recent studies have identified a family of putative ammonium transporters; mRNA for two members of this family, Rh B-glycoprotein (RhBG) and Rh C-glycoprotein (RhCG), is expressed in the kidney. The purpose of this study was to determine the cellular location of RhBG and RhCG protein in the mouse kidney. We generated RhBG- and RhCG-specific anti-peptide antibodies. Immunoblot analysis confirmed that both proteins were expressed in the mouse kidney. RhBG localization with immunohistochemistry revealed discrete basolateral labeling in the connecting segment (CNT) and in the majority of initial collecting tubule (ICT) and cortical collecting duct (CCD) cells. In the outer medullary collecting duct (OMCD) and inner medullary collecting duct (IMCD) only a subpopulation of cells exhibited basolateral immunoreactivity. Colocalization of RhBG with carbonic anhydrase II, the thiazide-sensitive transporter, and the anion exchangers AE1 and pendrin demonstrated RhBG immunoreactivity in all CNT cells and all CCD and ICT principal cells. In the ICT and CCD, basolateral RhBG immunoreactivity is also present in A-type intercalated cells but not in pendrin-positive CCD intercalated cells. In the OMCD and IMCD, only intercalated cells exhibit RhBG immunoreactivity. Immunoreactivity for a second putative ammonium transporter, RhCG, was present in the apical region of cells with almost the same distribution as RhBG. However, RhCG immunoreactivity was present in all CCD cells, and it was present in outer stripe OMCD principal cells, in addition to OMCD and IMCD intercalated cells. Thus the majority of RhBG and RhCG protein expression is present in the same epithelial cell types in the CNT and collecting duct but with opposite polarity. These findings suggest that RhBG and RhCG may play important and cell-specific roles in ammonium transport and signaling in these regions of the kidney.