Journal
KIDNEY INTERNATIONAL
Volume 79, Issue 2, Pages 154-161Publisher
ELSEVIER SCIENCE INC
DOI: 10.1038/ki.2010.386
Keywords
ammonium excretion; collecting duct; distal renal tubular acidosis; kidney ontogeny; rhesus proteins
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Funding
- EU [201590]
- Swiss National Science Foundation
- Zurich Center for Integrative Human Physiology
- Belgian agency FNRS
- Belgian agency FRSM
- Fondation Alphonse Jean Forton
- Inter-university Attraction Pole [IUAP P6/05]
- Communaute Francaise de Belgique
- Institut National de la Sante et de la Recherche Medicale
- Facility for Renal Phenotyping at the Centre de Recherche des Cordeliers
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Urinary acidification is a complex process requiring the coordinated action of enzymes and transport proteins and resulting in the removal of acid and the regeneration of bicarbonate. Proton secretion is mediated by luminal H+-ATPases and requires the parallel movement of NH3, and its protonation to NH4+, to provide sufficient buffering. It has been long assumed that ammonia secretion is a passive process occurring by means of simple diffusion driven by the urinary trapping of ammonium. However, new data indicate that mammalian cells possess specific membrane proteins from the family of rhesus proteins involved in ammonia/mu m permeability. Rhesus proteins were first identified in yeast and later also in plants, algae, and mammals. In rodents, RhBG and RhCG are expressed in the collecting duct, whereas in humans only RhCG was detected. Their expression increases with maturation of the kidney and accelerates after birth in parallel with other acid-base transport proteins. Deletion of RhBG in mice had no effect on renal ammonium excretion, whereas RhCG deficiency reduces renal ammonium secretion strongly, causes metabolic acidosis in acid-challenged mice, and impairs restoration of normal acid-base status. Microperfusion experiments or functional reconstitution in liposomes demonstrates that ammonia is the most likely substrate of RhCG. Similarly, crystal structures of human RhCG and the homologous bacterial AmtB protein suggest that these proteins may form gas channels. Kidney International (2011) 79, 154-161; doi:10.1038/ki.2010.386; published online 6 October 2010
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