Figure 8.

Ammonia transport in the thick ascending limb (TAL). The primary mechanism of ammonia reabsorption in the TAL is via substitution of NH₄⁺ for K⁺ and transport by Na⁺-K⁺-2Cl⁻ cotransporter 2 (NKCC-2). Electroneutral K⁺/NH₄⁺ exchange and conductive K⁺transport are also present, but quantitatively less significant components of apical K⁺ transport. Diffusive NH₃ transport across the apical plasma membrane is present, but not quantitatively significant. Cytosolic NH₄⁺ can exit via basolateral NHE-4. A second mechanism of basolateral NH₄⁺ exit may involve dissociation to NH₃ and H⁺, with NH₃ exit via an uncharacterized, presumably diffusive, mechanism, and buffering of intracellular H⁺ released via NBCn1-mediated HCO³⁻ entry. Figure modified from reference (180) with permission.