Modulation of gastric H+,K+-transporting ATPase function by sodium.
Gastric H+,K+-ATPase activity is not affected by Na+ at pH 7.0 but is significantly stimulated by Na+ at pH 8.5. For the stimulation at the latter pH, the presence of both Na+ and K+ were essential. Contrary the H+,K+-ATPase, the associated K+-pNPPase was inhibited by Na+ at both pH values. Sodium competes with K+ for the K+-pNPPase reaction. Also, unlike the H+, K+-ATPase activity the ATPase-mediated transport of H+ within the gastric microsomal vesicles was inhibited by Na+. For the latter event only the extravesicular and not the intravesicular Na+ was effective. The data suggest that the K+-pNPPase activity does not represent the phosphatase step of the H+,K+-ATPase reaction. In addition, the observed inhibition of vesicular H+ uptake by Na+ appears to be due to the displacement by Na+ of a cytosolic (extravesicular) H+ site responsible for the vectorial translocation of H+.
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D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D017506:H(+)-K(+)-Exchanging ATPase; D006863:Hydrogen-Ion Concentration; D008861:Microsomes / Q000201:enzymology; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D011522:Protons; D012964:Sodium / Q000494:pharmacology*; D013270:Stomach / Q000201:enzymology*; D013552:Swine
D011522:Protons; D012964:Sodium; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase