Figure 1.

A simplified model for the secretion of gastric acid by the parietal cell. The H⁺,K⁺-ATPase located on the apical membrane of the parietal cell exchanges H⁺ for K⁺. K⁺ is recycled from the canaliculus into the cytoplasm by K⁺ channels in the apical membrane. The combined actions of K⁺ channels and enzymes on the basolateral membrane regulate cytoplasmic K⁺ levels. Cl^- enters the cell cytoplasm via a Cl^-/HCO₃^- exchanger and moves from the cytoplasm into the canaliculus via a Cl^- channel (most likely ClC-2).