Omeprazole decreases H(+)-K(+)-ATPase protein and increases permeability of oxyntic secretory membranes in rabbits.
Amounts and fractional distributions of gastric H(+)-K(+)-adenosinetriphosphatase (ATPase) activity and H(+)-K(+)-ATPase protein as well as properties of H(+)-K(+)-ATPase-containing membranes were studied in rabbits injected with omeprazole (OM; 1 mg/kg sc twice daily for 5 days). Total H(+)-K(+)-ATPase activity decreased to 22 +/- 2% of control (n = 4). Densitometry of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blots showed H(+)-K(+)-ATPase protein was decreased to 60-70% of control. In vitro reduction of the enzyme-OM disulfide bond with 0.1 M 2-mercaptoethanol increased microsomal H(+)-K(+)-ATPase activity to 56 +/- 7% of control (n = 3), consistent with a substantial decrease in enzyme protein. Incorporation of 35S-labeled methionine for 30 min before death resulted in 2.2-fold more label per unit of microsomal alpha-subunit protein (5 days OM vs. control). Thus the decrease in enzyme protein resulted from increased breakdown rather than decreased synthesis. A striking shift in distribution of H(+)-K(+)-ATPase-containing microsomes (tubulovesicles) on sucrose gradients reflected slow equilibration of most control vesicles with the gradient medium and faster equilibration after 5 days OM, indicating increased permeability. After 5 days OM, microsomal vesicle acidification (by acridine orange uptake assay) was negligible, even with 2-mercaptoethanol treatment, and H+ leakage on sudden delta pH was faster than control. We conclude that extended OM treatment not only inhibits H(+)-K(+)-ATPase but accelerates its breakdown and renders H(+)-K(+)-ATPase-containing membranes more permeable. It is thus possible that increased backward H+ flux contributes to profound inhibition of acid secretion during extended omeprazole treatment. In parallel experiments, H(+)-K(+)-ATPase activity and density gradient sedimentation of tubulovesicles returned to near normal 3 days after OM withdrawal.
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
J M
JM
Crothers
D C
DC
Chow
J G
JG
Forte
D000165:Acridine Orange; D000818:Animals; D002463:Cell Membrane Permeability; D002499:Centrifugation, Density Gradient; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology; D009550:Nigericin / Q000494:pharmacology; D009853:Omeprazole / Q000494:pharmacology*; D009995:Osmosis; D010295:Parietal Cells, Gastric / Q000378:metabolism*; D011817:Rabbits; D013347:Subcellular Fractions / Q000378:metabolism; D013395:Sucrose / Q000494:pharmacology; D014018:Tissue Distribution
D013395:Sucrose; D017506:H(+)-K(+)-Exchanging ATPase; D000165:Acridine Orange; D009853:Omeprazole; D009550:Nigericin