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Role of NH 3 and NH 4 + transporters in renal acid-base transport

2010; American Physical Society; Volume: 300; Issue: 1 Linguagem: Inglês

10.1152/ajprenal.00554.2010

1931-857X

I. David Weiner, Jill W. Verlander,

Nitric Oxide and Endothelin Effects

Renal ammonia excretion is the predominant component of renal net acid excretion. The majority of ammonia excretion is produced in the kidney and then undergoes regulated transport in a number of renal epithelial segments. Recent findings have substantially altered our understanding of renal ammonia transport. In particular, the classic model of passive, diffusive NH 3 movement coupled with NH 4 + “trapping” is being replaced by a model in which specific proteins mediate regulated transport of NH 3 and NH 4 + across plasma membranes. In the proximal tubule, the apical Na + /H + exchanger, NHE-3, is a major mechanism of preferential NH 4 + secretion. In the thick ascending limb of Henle's loop, the apical Na + -K + -2Cl − cotransporter, NKCC2, is a major contributor to ammonia reabsorption and the basolateral Na + /H + exchanger, NHE-4, appears to be important for basolateral NH 4 + exit. The collecting duct is a major site for renal ammonia secretion, involving parallel H + secretion and NH 3 secretion. The Rhesus glycoproteins, Rh B Glycoprotein (Rhbg) and Rh C Glycoprotein (Rhcg), are recently recognized ammonia transporters in the distal tubule and collecting duct. Rhcg is present in both the apical and basolateral plasma membrane, is expressed in parallel with renal ammonia excretion, and mediates a critical role in renal ammonia excretion and collecting duct ammonia transport. Rhbg is expressed specifically in the basolateral plasma membrane, and its role in renal acid-base homeostasis is controversial. In the inner medullary collecting duct (IMCD), basolateral Na + -K + -ATPase enables active basolateral NH 4 + uptake. In addition to these proteins, several other proteins also contribute to renal NH 3 /NH 4 + transport. The role and mechanisms of these proteins are discussed in depth in this review.