Figure 1.

Proximal tubular Na ⁺ reabsorption. Active Na⁺ transport mediated by basolateral NKA provides the driving force for proximal tubular Na⁺ transport. Transporters in the apical membrane include NHE3, SGLT, and NaPi2. NHE3 is considered to be responsible for most of the Na⁺ reabsorption from the glomerular filtrate. NBCe1 at the basolateral membrane plays an important role not only in Na⁺ homeostasis but also in the systemic acid/base balance. NKA, Na⁺/K⁺ ATPase; NHE3, Na⁺/H⁺ exchanger isoform 3; NBCe1, Na⁺/HCO₃⁻ cotransporter; Glu, glucose; SGLT, Na⁺/glucose cotransporter; NaPi2, Na⁺/phosphate cotransporter type 2.