Valinomycin induced energy-dependent mitochondrial swelling,cytochrome <Emphasis Type="Italic">c</Emphasis> release,cytosolic NADH/cytochrome <Emphasis Type="Italic">c</Emphasis> oxidation and apoptosis |
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Authors: | Dario Domenico Lofrumento Gianluigi La Piana Daniela Isabel Abbrescia Valeria Palmitessa Velia La Pesa Domenico Marzulli Nicola Elio Lofrumento |
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Institution: | (1) Department of Biochemistry and Molecular Biology, University of Bari, Via Orabona 4, 70126 Bari, Italy;(2) Department of Biological and Environmental Sciences and Technologies, Section of Human Anatomy, University of Salento, Lecce, Italy;(3) Institute of Biomembranes and Bioenergetics (IBBE) (CNR), University of Bari, Bari, Italy; |
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Abstract: | In valinomycin induced stimulation of mitochondrial energy dependent reversible swelling, supported by succinate oxidation,
cytochrome c (cyto-c) and sulfite oxidase (Sox) both present in the mitochondrial intermembrane space (MIS)] are released outside. This effect
can be observed at a valinomycin concentration as low as 1 nM. The rate of cytosolic NADH/cyto-c electron transport pathway is also greatly stimulated. The test on the permeability of mitochondrial outer membrane to exogenous
cyto-c rules out the possibility that the increased rate of exogenous NADH oxidation could be ascribed either to extensively damaged
or broken mitochondria. Accumulation of potassium inside the mitochondria, mediated by the highly specific ionophore valinomycin,
promotes an increase in the volume of matrix (evidenced by swelling) and the interaction points between the two mitochondrial
membranes are expected to increase. The data reported and those previously published are consistent with the view that “respiratory
contact sites” are involved in the transfer of reducing equivalents from cytosol to inside the mitochondria both in the absence
and the presence of valinomycin. Magnesium ions prevent at least in part the valinomycin effects. Rather than to the dissipation
of membrane potential, the pro-apoptotic property of valinomycin can be ascribed to both the release of cyto-c from mitochondria to cytosol and the increased rate of cytosolic NADH coupled with an increased availability of energy in
the form of glycolytic ATP, useful for the correct execution of apoptotic program. |
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