From blood typing to a transport metabolon at a crossroad. Focus on “Ammonium-dependent sodium uptake in mitochondrion-rich cells of medaka (Oryzias latipes) larvae”

Abstract

The Rh blood group-related proteins have recently been recognized as ammonia transporters acting in erythrocyte and non-erythrocyte membranes. They play an important role in excretion of nitrogenous waste formed mainly from amino acid metabolism. Because of a restricted availability of water, most terrestrial animals detoxify ammonia into urea or uric acid before removal from the body. However, aquatic animals, living in an abundant supply of water, can directly excrete ammonia into the environment immediately as it is produced. This method of ammonia elimination is strategic in avoiding urea synthesis, an anabolic process requiring ATP. In this issue of Am J Physiol Cell Physiol, Wu et al. (28) added further twist to this adaptive strategy by providing evidence for a coupling of the ammonia excretion with a sodium uptake process, which is essential for living in freshwater conditions.