Figure 7.

Reabsorption of HCO₃ in the distal nephron is mediated by apical H⁺ secretion by the α-intercalated cell. Two transporters secrete H⁺, a vacuolar H⁺-ATPase and an H⁺-K⁺-ATPase. The H⁺-K⁺-ATPase uses the energy derived from ATP hydrolysis to secrete H⁺ into the lumen and reabsorb K⁺ in an electroneutral fashion. The activity of the H⁺-K⁺-ATPase increases in K⁺ depletion and, thus, provides a mechanism by which K⁺ depletion enhances both collecting duct H⁺ secretion and K⁺ absorption.