title: Phosphatidylinositol is essential determinant for K+ permeability involved in gastric proton pumping.
abstract: Gastric vesicles purified from acid-secreting rabbit stomach display K(+) permeability manifested by the valinomycin-independent proton pumping of H(+)-K(+)-ATPase as monitored by acridine orange quenching. This apparent K(+) permeability is attenuated by the treatment of the membrane with 5 mM Mg(2+), and this phenomenon has been attributed to membrane-bound phosphoprotein phosphatase. However, with the exception of the nonspecific inhibitor pyrophosphate, protein phosphatase inhibitors failed to inhibit the loss of K(+) permeability. Preincubation of the membrane with neomycin, a phospholipase C inhibitor, surrogated the effect of Mg(2+), whereas another inhibitor, U-73122, did not. Phosphatidylinositol 4,5-bisphosphate (PIP(2)) restored the attenuated K(+) permeability by treatment with either Mg(2+) or neomycin. Furthermore, either phosphatidylinositol bound to phosphatidylinositol transfer protein or phosphatidylinositol 4,5,6-trisphosphate (PIP(3)) surrogated the effect of PIP(2). Mg(2+) and neomycin reduced K(+) permeability in the membrane as determined by Rb(+) influx and K(+)-dependent H(+) diffusion. Treatment with Mg(2+) reduced the contents of PIP(2) and PIP(3) in the membrane. These results suggest that PIP(2) and/or PIP(3) maintain K(+) permeability, which is essential for proton pumping in the apical membrane of the secreting parietal cell.
authors.affiliation: Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Omi
authors.forename: T
authors.initials: T
authors.lastname: Nagao
authors.forename: T
authors.initials: T
authors.lastname: Urushidani
mesh_terms: D000165:Acridine Orange; D000617:Aminoglycosides; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002413:Cations, Divalent / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005753:Gastric Mucosa / Q000737:chemistry / Q000378:metabolism*; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism*; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008565:Membrane Proteins; D010539:Permeability / Q000187:drug effects; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000032:analysis / Q000494:pharmacology; D018129:Phosphatidylinositol Phosphates / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012413:Rubidium / Q000493:pharmacokinetics; D022142:Secretory Vesicles / Q000737:chemistry / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D002352:Carrier Proteins; D002413:Cations, Divalent; D004791:Enzyme Inhibitors; D046911:Macromolecular Substances; D008565:Membrane Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D049294:Phospholipid Transfer Proteins; D010749:Phosphoprotein Phosphatases; D010738:Type C Phospholipases; D017506:H(+)-K(+)-Exchanging ATPase; D000165:Acridine Orange; D008274:Magnesium; D012413:Rubidium; D011188:Potassium