RhBG and RhCG, the Putative Ammonia Transporters, Are Expressed in the Same Cells in the Distal Nephron

Abstract

Abstract. Two nonerythroid homologs of the blood group Rh proteins, RhCG and RhBG, which share homologies with specific ammonia transporters in primitive organisms and plants, could represent members of a new family of proteins involved in ammonia transport in the mammalian kidney. Consistent with this hypothesis, the expression of RhCG was recently reported at the apical pole of all connecting tubule (CNT) cells as well as in intercalated cells of collecting duct (CD). To assess the localization along the nephron of RhBG, polyclonal antibodies against the Rh type B glycoprotein were generated. In immunoblot experiments, a specific polypeptide of Mr approximately 50 kD was detected in rat kidney cortex and in outer and inner medulla membrane fractions. Immunocytochemical studies revealed RhBG expression in distal nephron segments within the cortical labyrinth, medullary rays, and outer and inner medulla. RhBG expression was restricted to the basolateral membrane of epithelial cells. The same localization was observed in rat and mouse kidney. RT-PCR analysis on microdissected rat nephron segments confirmed that RhBG mRNAs were chiefly expressed in CNT and cortical and outer medullary CD. Double immunostaining with RhCG demonstrated that RhBG and RhCG were coexpressed in the same cells, but with a basolateral and apical localization, respectively. In conclusion, RhBG and RhCG are present in a major site of ammonia secretion in the kidney, i.e., the CNT and CD, in agreement with their putative role in ammonium transport.

Rhesus glycoprotein gene expression in the mangrove killifishKryptolebias marmoratusexposed to elevated environmental ammonia levels and air

“…The amino acid sequences of these three Rh genes share high homology to known Rh sequences in the GenBank. Since all three Rh proteins contain potential N-glycosylation sites, they are probably expressed as glycoproteins, similar to their mammalian counterparts (Quentin et al, 2003). K. marmoratus RhBG shares higher sequence homology to three-spined stickleback (Gasterosteus aculeatus) (data not shown), which C. Y. C. Hung and others and RhCG2 in control (0·mmol·l -1 ammonia) and ammonia-exposed (2·mmol·l -1 ammonia) K. marmaratus.…”

“…In the mammalian kidney, polarized localization of the Rh proteins is observed in epithelial cells of specific regions, including the renal collecting segment and the collecting duct, with RhBG expression in the basolateral membrane and RhCG in the apical membrane (Quentin et al, 2003;Verlander et al, 2003). Such polarized localization is also present in the pufferfish.…”

“…FGMFVTLVFASVGGSLGGLLLRLPFLDSPPDSQCFEDQVYWEVPGEQETET-QRPLRGGESDTRA--- THE JOURNAL OF EXPERIMENTAL BIOLOGY been shown to be glycoproteins (Quentin et al, 2003) and therefore, potential N-glycosylation sites on killifish Rh protein sequences were predicted via NetNGlyc 1.0 Server at http://www.cbs.dtu.dk/services/NetNGlyc.…”

Kidney Protein Dynamics and Ammoniagenesis in Humans with Chronic Metabolic Acidosis

“…NH 4 ϩ could pass freely across lipid bilayers through concentration gradients or could be transported by specific carriers (29). The distribution of NH 4 ϩ into the urine augments the effects of the increase in ammoniagenesis on acid-base balance in as much as only ammonia excreted in the urine corresponds to a bicarbonate gain.…”

Evidence of a Structural and Functional Ammonium Transporter RhBG·Anion Exchanger 1·Ankyrin-G Complex in Kidney Epithelial Cells

“…Rabbit polyclonal antiserum against the cytoplasmic N terminus of AE1 was a gift from Dr. Carsten Wagner (University of Zürich, Zürich, Switzerland). Rabbit and A-08 mouse polyclonal antibodies raised against, respectively, the cytoplasmic C terminus and extracellular loops of human RhBG have been described previously (1,2,18). Mouse anti-human ankyrin-G and anti-ZO-1 (Alexa Fluor 488-conjugated) monoclonal antibodies were purchased from Invitrogen and Molecular Probes (SaintAubin, France), respectively.…”