Figure 1.

Major players in gastric acid secretion. Apical secretion of hydrochloric acid by the parietal cell requires three ion transport processes: an H⁺/K⁺-ATPase-mediated exchange of intracellular hydrogen ion for an extracellular potassium ion, and chloride secretion and potassium recycling, which are necessary to maintain electroneutrality and avoid luminal potassium depletion. Secretion is mainly regulated by activation: (i) of receptors for the secretagogues acetylcholine, histamine, and gastrin that are mainly secreted by the enteric nervous system, enterochromaffin-like (ECL) cells, and G cells, respectively, and (ii) of receptors for inhibitory somatostatin released by D cells.