Final answer:
In the basolateral membrane of proximal tubular cells, bicarbonate is moved out of the cells by both K⁺/HCO₃- and HCO₃-/Cl⁻ countertransporters in an antiport mechanism.
Step-by-step explanation:
In the basolateral membrane of proximal tubular cells, bicarbonate is moved out of the cells by both K⁺/HCO₃- and HCO₃-/Cl⁻ countertransporters. Sodium ions are reabsorbed from the filtrate in exchange for hydrogen ions by an antiport mechanism in the apical membranes of cells lining the renal tubule. Inside the cell, carbonic acid is catalyzed into CO₂ and water, which diffuse across the apical membrane. Bicarbonate ions are cotransported with sodium across the basal membrane to the interstitial space.