title: Effects of ionophores on the phospholipid flippase activity of gastric vesicles.
abstract: Recently, a gastric Mg(2+)-ATP-dependent phospholipid flippase was found. Here, the effects of ionophores and monovalent cations on the gastric flippase were examined. We found that translocation of the fluorescent analogue of phosphatidylcholine was inhibited by valinomycin in the presence of K(+). The inhibition depended on both the concentrations of valinomycin and K(+). Valinomycin did not inhibit translocation in the absence of K(+). Protonophores, carbonylcyanide-m-chlorophenylhydrazone (CCCP) and carbonylcyanide-p-(trifluoromethoxy)phenylhydrazone (FCCP), accelerated translocation by 190-270%. These increases were completely abolished by 2-methyl-8-(phenylmethoxy)imidazo-[1, 2-a]pyridine-3-acetonitrile (SCH 28080), a gastric flippase inhibitor. Since these protonophores did not affect the Mg(2+)-dependent ATPase activity that is responsible for phospholipid translocation by the flippase, the coupling ratio of the amount of transported phospholipids/the amount of hydrolyzed ATP was variable and seemed to depend on the state of the membrane bilayer, for example fluidity. Inhibition by the valinomycin-K(+) complex was abolished in the presence of CCCP or FCCP, indicating the valinomycin-K(+)-CCCP(FCCF) ternary complex did not inhibit the flippase.
authors.affiliation: Department of Pharmaceutical Physiology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, 930-0194, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
authors.forename: M
authors.initials: M
authors.lastname: Morii
authors.forename: N
authors.initials: N
authors.lastname: Takeguchi
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005753:Gastric Mucosa / Q000201:enzymology*; D006096:Gramicidin / Q000494:pharmacology; D007425:Intracellular Membranes / Q000201:enzymology; D007476:Ionophores / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000493:pharmacokinetics / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D013552:Swine; D014634:Valinomycin / Q000494:pharmacology
chemical_list: C078632:1-acyl-2-(12-((7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl)phosphatidylcholine; D000900:Anti-Bacterial Agents; D007476:Ionophores; D018942:Macrolides; D010713:Phosphatidylcholines; D006096:Gramicidin; D014634:Valinomycin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D012965:Sodium Chloride; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D011189:Potassium Chloride; D017301:Ca(2+) Mg(2+)-ATPase; D009327:4-Chloro-7-nitrobenzofurazan; C050476:nonactin