Disulfide cross-linking of H,K-ATPase opens Cl- conductance, triggering proton uptake in gastric vesicles. Studies with specific inhibitors.
An S-S cross-linking reagent, Cu2+-o-phenanthroline, increased the 36Cl-/Cl- exchange rate across the hog gastric vesicle membrane, which contains H,K-ATPase, but did not affect the 86Rb+/Rb+ exchange rate. The results show that closed Cl- conductance can be opened by S-S cross-linking. Gastric vesicles with opened Cl- conductance could take up H+ upon addition of MgATP without prolonged preincubation in a solution containing K+. Preincubation of gastric vesicles with picoprazole, which is a specific inhibitor of H,K-ATPase and binds to 100-kDa polypeptides of the enzyme, dose dependently inhibited opening of the Cl- conductance by Cu2+-o-phenanthroline, indicating that the Cl- conductance is part of the function of the H,K-ATPase. The effect of picoprazole was greater at alkaline pH than at acidic pH. Another H,K-ATPase inhibitor, 2-[2-(3,5-dimethyl-4-methoxy)-pyridylmethylsulfinyl] (5-methoxycarbonyl-6-methyl)-benzimidazole (H compound), had a similar but stronger effect on the Cl- conductance than that of picoprazole. A pungent ingredient of curry, allylisothiocyanate, caused similar pH-dependent inhibition to that of picoprazole. However, another substituted benzimidazole, omeprazole, did not inhibit Cl- conductance. Substituted benzimidazoles, such as picoprazole, H compound, and omeprazole, inhibited the H,K-ATPase activity progressively with a decrease in pH of the medium. This pH dependence was the reverse of that in inhibition of Cl- conductance, suggesting that the inhibitory site of Cl- conductance is different from that of the H,K-ATPase activity and that the conformational states of the two sites change in different ways with change in pH of the medium.
D053799:2-Pyridinylmethylsulfinylbenzimidazoles; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D004220:Disulfides / Q000378:metabolism*; D004553:Electric Conductivity; D017506:H(+)-K(+)-Exchanging ATPase; D017879:Isothiocyanates; D008433:Mathematics; D009853:Omeprazole; D010618:Phenanthrolines / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D011522:Protons; D012413:Rubidium / Q000378:metabolism; D013270:Stomach / Q000201:enzymology*; D013552:Swine; D013861:Thiocyanates / Q000494:pharmacology
D053799:2-Pyridinylmethylsulfinylbenzimidazoles; D001562:Benzimidazoles; D002712:Chlorides; D004220:Disulfides; D017879:Isothiocyanates; D010618:Phenanthrolines; D011522:Protons; D013861:Thiocyanates; C037152:isothiocyanic acid; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D009853:Omeprazole; D012413:Rubidium; D011188:Potassium; C028887:picoprazole; C025205:1,10-phenanthroline