1. Ammonia secretion by the collecting duct.
Ammonia secretion by the collecting duct. Ammonia uptake across the basolateral membrane primarily involves either transporter-mediated uptake across the basolateral membrane by Rhbg or Rhcg, with a component of diffusive NH3 absorption. Cytosolic NH3 is transported across the apical membrane by a combination of Rhcg and diffusive transport. In the IMCD, but not the CCD, basolateral Na+-K+-ATPase also contributes to NH4+ uptake across the basolateral membrane. Cytosolic H+ is generated by a carbonic anhydrase II–mediated mechanism, and is secreted across the apical membrane via H+-ATPase and H+-K+-ATPase. Luminal H+ titrates luminal NH3, forming NH4+ and maintaining a low luminal NH3 concentration necessary for NH3 secretion. CAII, carbonic anhydrase isoform II; Rhbg, Rhesus B glycoprotein; Rhcg, Rhesus C glycoprotein.
I. David Weiner et al. CJASN 2015;10:
©2015 by American Society of Nephrology