CHARACTERISTICS OF CA-2+ TRANSPORT BY CORN MITOCHONDRIA

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CALCIUM-TRANSPORT BY CORN MITOCHONDRIA - EVALUATION OF THE ROLE OF PHOSPHATE

Mitochondria from some plant tissues possess the ability to take up Ca2+ by a phosphate-dependent mechanism associated with a decrease in membrane potential, H+ extrusion, and increase in the rate of respiration (AE Vercesi, L Pereira da Silva, IS Martins, CF Bernardes, EGS Carnieri, MM Fagian [1989] ln G Fiskum, ed, Cell Calcium Metabolism. Plenum Press, New York, pp 103-111). The present study reexamined the nature of the phosphate requirement in this process. The main observations are: (a) Respiration-coupled Ca2+ uptake by isolated corn (Zea mays var Maya Normal) mitochondria or carbonyl cyanide p-trifluoromethoxyphenylhydrazone-induced efflux of the cation from such mitochondria are sensitive to mersalyl and cannot be dissociated from the silmultaneous movement of phosphate in the same direction. (b) Ruthenium red-induced efflux is not affected by mersalyl and can occur in the absence of phosphate movement. (c) In Ca2+-loaded corn mitochondria, mersalyl causes net Ca2+ release unrelated to a decrease in membrane potential, probably due to an inhibition of Ca2+ cycling at the level of the influx pathway. It is concluded that corn mitochondria (and probably other plant mitochondria) do possess an electrophoretic influx pathway that appears to be a mersalyl-sensitive Ca2+/inorganic phosphate-symporter and a phosphate-independent efflux pathway possibly similar to the Na2+-independent Ca2+ efflux mechanism of vertebrate mitochondria, because it is not stimulated by Na+.98245245

Ca2+ induces a cyclosporin A-insensitive permeability transition pore in isolated potato tuber mitochondria mediated by reactive oxygen species

Oxidative damage of mammalian mitochondria induced by Ca2+ and prooxidants is mediated by the attack of mirochondria-generated reactive oxygen species on membrane protein thiols promoting oxidation and cross-linkage that leads to the opening of the mitochondrial permeability transition pore (Castilho et al., 1995). In this study, we present evidence that deenergized potato tuber (Solanum tuberosum) mitochondria, which do not possess a Ca2+ uniport, undergo inner membrane permeabilization when treated with Ca2+ (>0.2 mM), as indicated by mitochondrial swelling. Similar to rat liver mitochondria, this permeabilization is enhanced by diamide, a thiol oxidant that creates a condition of oxidative stress by oxidizing pyridine nucleotides. This is inhibited by the antioxidants catalase and dithiothreitol. Potato mitochondrial membrane permeabilization is not inhibited by ADP, cyclosporin A, and ruthenium red, acid is partially inhibited by Mg2+ and acidic pH, well known inhibitors of the mammalian mitochondrial permeability transition. The lack of inhibition of potato mitochondrial permeabilization by cyclosporin A is in contrast to the inhibition of the peptidylprolyl cis-trans isomerase activity, that is related to the cyclosporin A-binding protein cyclophilin. Interestingly, the monofunctional thiol reagent mersalyl induces an extensive cyclosporin A-insensitive potato mitochondrial swelling, even in the presence of lower Ca2+ concentrations (>0.01 mM). In conclusion, we have identified a cyclosporin A-insensitive permeability transition pore in isolated potato mitochondria that is induced by reactive oxygen species.331435

Functional characterization of mitochondria isolated from the ancient gymnosperm Araucaria angustifolia

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Mitochondria were isolated from embryogenic cell cultures of Araucaria angustifolia, an ancient gymnosperm. The mitochondria obtained oxidized NADH and succinate as respiratory substrates and were able to sustain a high transmembrane electrical potential. They were able to take up Ca2+ supported by substrate oxidation, sensitive to ruthenium red and dependent on membrane potential. The influx of the ion was Pi dependent and at least one efflux pathway was demonstrated by ruthenium red addition. The mitochondria also oxidized externally added NADH, and presented oxygen consumption insensitive to cyanide and sensitive to salicyl hydroxamic acid (SHAM) suggesting the presence of external NADH dehydrogenase and alternative oxidase (AOX), respectively. Besides, mitochondria were uncoupled, in the absence of BSA, by the addition of oleic acid suggesting the presence of the plant uncoupling mitochondrial protein. (C) 2008 Elsevier Ireland Ltd. All rights reserved.1755701705Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES