Molecular Mechanisms of Renal Ammonia Transport

Acid-base homeostasis to a great extent relies on renal ammonia metabolism. In the past several years, seminal studies have generated important new insights into the mechanisms of renal ammonia transport. In particular, the theory that ammonia transport occurs almost exclusively through nonionic NH3 diffusion and NH4⁺ trapping has given way to a model postulating that a variety of proteins specifically transport NH3 and NH4⁺ and that this transport is critical for normal ammonia metabolism. Many of these proteins transport primarily H⁺ or K⁺ but also transport NH4⁺. Nonerythroid Rh glycoproteins transport ammonia and may represent critical facilitators of ammonia transport in the kidney. This review discusses the underlying aspects of renal ammonia transport as well as specific proteins with important roles in renal ammonia transport.