title: Anacardic acid-mediated changes in membrane potential and pH gradient across liposomal membranes.
abstract: We have previously shown that anacardic acid has an uncoupling effect on oxidative phosphorylation in rat liver mitochondria using succinate as a substrate (Life Sci. 66 (2000) 229-234). In the present study, for clarification of the physicochemical characteristics of anacardic acid, we used a cyanine dye (DiS-C3(5)) and 9-aminoacridine (9-AA) to determine changes of membrane potential (DeltaPsi) and pH difference (DeltapH), respectively, in a liposome suspension in response to the addition of anacardic acid to the suspension. The anacardic acid quenched DiS-C3(5) fluorescence at concentrations higher than 300 nM, with the degree of quenching being dependent on the log concentration of the acid. Furthermore, the K(+) diffusion potential generated by the addition of valinomycin to the suspension decreased for each increase in anacardic acid concentration used over 300 nM, but the sum of the anacardic acid- and valinomycin-mediated quenching was additively increasing. This indicates that the anacardic acid-mediated quenching was not due simply to increments in the K(+) permeability of the membrane. Addition of anacardic acid in the micromolar range to the liposomes with DeltaPsi formed by valinomycin-K(+) did not significantly alter 9-AA fluorescence, but unexpectedly dissipated DeltaPsi. The DeltaPsi preformed by valinomycin-K(+) decreased gradually following the addition of increasing concentrations of anacardic acid. The DeltaPsi dissipation rate was dependent on the pre-existing magnitude of DeltaPsi, and was correlated with the logarithmic concentration of anacardic acid. Furthermore, the initial rate of DeltapH dissipation increased with logarithmic increases in anacardic acid concentration. These results provide the evidence for a unique function of anacardic acid, dissimilar to carbonylcyanide p-trifluoromethoxyphenylhydrazone or valinomycin, in that anacardic acid behaves as both an electrogenic (negative) charge carrier driven by DeltaPsi, and a 'proton carrier' that dissipates the transmembrane proton gradient formed.
authors.affiliation: Science of Biological Function, Life Science, Graduate School of Agriculture, Tohoku University, Sendai, Japan. toyomizu@bios.tohoku.ac.jp
authors.forename: Masaaki
authors.initials: M
authors.lastname: Toyomizu
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Okamoto
authors.forename: Yukio
authors.initials: Y
authors.lastname: Akiba
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Nakatsu
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Konishi
mesh_terms: D000585:Aminacrine; D048729:Anacardic Acids; D052160:Benzothiazoles; D002232:Carbocyanines; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes; D006096:Gramicidin / Q000737:chemistry; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D008081:Liposomes / Q000737:chemistry*; D008564:Membrane Potentials / Q000187:drug effects; D008956:Models, Chemical; D015394:Molecular Structure; D012459:Salicylates / Q000737:chemistry / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence / Q000379:methods; D014634:Valinomycin / Q000737:chemistry
chemical_list: D048729:Anacardic Acids; D052160:Benzothiazoles; D002232:Carbocyanines; D005456:Fluorescent Dyes; D008081:Liposomes; D012459:Salicylates; D006096:Gramicidin; C088115:anacardic acid; D014634:Valinomycin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; C012944:3,3'-dipropyl-2,2'-thiadicarbocyanine; D000585:Aminacrine