Abstract
Characteristics of the (H++K+)-ATPase from hog gastric mucosa were examined in relation to ATPase activity and proton uptake as functions of the osmotic states of the gastric vesicles. When osmotically expanded by the presence ofan internal, hyper concentration of NaCl, choline Cl, or sucrose, ATPase activity increased as the internal osmolality was increased with 15 mM of external KCl;but, no proton uptake was found. When the gastric vesicles had expanded because of the internal KCl, ATPase activity increased and was accompanied by proton uptake. This indicates that an idle, uncoupling mechanism of the ATPase worked in the absence of internal, transportable K+. Shrinkage of vesicles, caused by external sucrose, induced a decrease in ATPase activity in the presence of 15 mM of external KCl (the internal medium was sucrose only) that was not accompanied by proton uptake. Shrinkage due to NaCl induced greater inhibition than did sucrose, evidences that competitive binding of Na+ to the ATP site as well as through itsshrinking effect. The results of this study are important because the osmotic expansion of vesicles is thought to produce morphological changes in the apical membrane of parietal cells and the onset of acid secretion.
