The gastric H+,K+-ATPase: the site of action of omeprazole.

The mammalian parietal cell is dedicated to the secretion of HCl in response to various stimuli and second messengers. Oxidative metabolism in the cell increases about 10-fold in order to supply ATP to the gastric proton pump, the H+,K+-ATPase. This pump appears to be present only in the parietal cell. This membrane-embedded enzyme uses the scalar energy of ATP hydrolysis to carry out the vectorial transport of H+ in one direction in exchange for K+ in the other direction. In the cytoplasmic vesicle, K+ does not permeate the membrane, whereas in the secretory canaliculus, there is a Cl- channel and a KCl cotransport pathway which allow K+ and Cl- to exit from the cell. The K+ is then recycled back into the cell by the ATPase, and H+ secretion occurs into the canalicular space. Although there are other proton pumps, only the gastric H+,K+-ATPase has this exchange mechanism and only the gastric H+,K+-ATPase is able to generate a pH of less than 4. Thus the gastric proton pump has a unique structure and mechanism, and produces a unique luminal pH. This enzyme is therefore an appropriate target for rational drug design.