Fluoxetine interacts with the lipid bilayer of the inner membrane in isolated rat brain mitochondria, inhibiting electron transport and F1F0-ATPase activity

The effects of fluoxetine on the oxidative phosphorylation of mitochondria isolated from rat brain and on the kinetic properties of submitochondrial p article F1F0-ATPase were evaluated. The state 3 respiration rate supported by pyruvate + malate, succinate, or ascorbate + tetramethyl-p-phenylenediam ine (TMPD) was substantially decreased by fluoxetine. The IC50 for pyruvate + malate oxidation was similar to 0.15 mM and the pattern of inhibition wa s the typical one of the electron-transport inhibitors, in that the drug in hibited both ADP- and carbonyl cyanide m-chlorophenylhydrazone (CCCP)-stimu lated respirations and the former inhibition was not released by the uncoup ler. Fluoxetine also decreased the activity of submitochondrial particle F1 F0-ATPase (IC50 similar to 0.08 mM) even though K-0.5 and activity of Trito n X-100 solubilized enzyme were not changed substantially. As a consequence of these effects, fluoxetine decreased the rate of ATP synthesis and depre ssed the phosphorylation potential of mitochondria. Incubation of mitochond ria or submitochondrial particles with fluoxetine under the conditions of r espiration or F1F0-ATPase assays, respectively, caused a dose-dependent enh ancement of 1-anilino-8-naphthalene sulfonate (ANS) fluorescence. These res ults show that fluoxetine indirectly and nonspecifically affects electron t ransport and F1F0)-ATPase activity inhibiting oxidative phosphorylation in isolated rat brain mitochondria. They suggest, in addition, that these effe cts are mediated by the drug interference with the physical state of lipid bilayer of inner mitochondrial membrane.