Protective action of tamoxifen on carboxyatractyloside-induced mitochondrial permeability transition

Mitochondrial permeability transition is established after massive Ca(2+) accumulation inside the matrix, in addition to an inducer. The closure of the pore can be accomplished by adenosine diphosphate and the immunosuppressant cyclosporin A. Recently, the estrogen antagonist, tamoxifen, has been introduced as an inhibitor of the opening of the permeability transition pore. However, the mechanism by which this drug inhibits pore opening is still under discussion. This work was performed with the purpose of establishing the membrane system involved in tamoxifen-induced pore closure. For this purpose, permeability transition was induced after the addition of carboxyatractyloside, which is a specific reagent that interacts with the adenine nucleotide translocase.

Permeability transition was assessed by analyzing matrix Ca(2+) release, transmembrane electric gradient, and mitochondrial swelling in aged, as well as in freshly prepared mitochondria. Also, cytochrome c content was analyzed in membrane mitochondria as well as in the supernatant.

In freshly prepared mitochondria, tamoxifen, at the concentration of 10 μM, totally inhibited nonspecific membrane permeability induced by 1 μM carboxyatractyloside. In addition, tamoxifen inhibited non-specific permeability in aged mitochondria and diminished membrane fluidity.

Plausibly, the inhibitory effect of tamoxifen on nonspecific membrane permeability, as induced by carboxyatractyloside, should be ascribed to a diminution, of membrane fluidity by this drug.