tacrolimus and antimycin

Changes in mitochondrial integrity, reactive oxygen species release and Ca2+ handling are proposed to be involved in the pathogenesis of many neurological disorders including methylmalonic acidaemia and Huntington's disease, which exhibit partial mitochondrial respiratory inhibition. In this report, we studied the mechanisms by which the respiratory chain complex II inhibitors malonate, methylmalonate and 3-nitropropionate affect rat brain mitochondrial function and neuronal survival. All three compounds, at concentrations which inhibit respiration by 50%, induced mitochondrial inner membrane permeabilization when in the presence of micromolar Ca2+ concentrations. ADP, cyclosporin A and catalase prevented or delayed this effect, indicating it is mediated by reactive oxygen species and mitochondrial permeability transition (PT). PT induced by malonate was also present in mitochondria isolated from liver and kidney, but required more significant respiratory inhibition. In brain, PT promoted by complex II inhibition was stimulated by increasing Ca2+ cycling and absent when mitochondria were pre-loaded with Ca2+ or when Ca2+ uptake was prevented. In addition to isolated mitochondria, we determined the effect of methylmalonate on cultured PC12 cells and freshly prepared rat brain slices. Methylmalonate promoted cell death in striatal slices and PC12 cells, in a manner attenuated by cyclosporin A and bongkrekate, and unrelated to impairment of energy metabolism. We propose that under conditions in which mitochondrial complex II is partially inhibited in the CNS, neuronal cell death involves the induction of PT.

Topics: Animals; Antimycin A; Bongkrekic Acid; Brain; Calcimycin; Calcium; Catalase; Cell Survival; Cyclosporins; Dose-Response Relationship, Drug; Drug Interactions; Electron Transport Complex II; Enzyme Inhibitors; Female; In Vitro Techniques; Ionophores; Malonates; Membrane Potentials; Methylmalonic Acid; Mitochondria; NADP; Neurons; Nitro Compounds; Oxygen Consumption; PC12 Cells; Permeability; Propionates; Rats; Rotenone; Tacrolimus; Tetrazolium Salts; Thiazoles; Uncoupling Agents

The nuclear gene encoding the Sit4 protein phosphatase was identified in the budding yeast Kluyveromyces lactis. K. lactis cells carrying a disrupted sit4 allele are resistant to oligomycin, antimycin, ketoconazole, and econazole but hypersensitive to paromomycin, sorbic acid, and 4-nitroquinoline-N-oxide (4-NQO). Overexpression of SIT4 leads to an elevation in resistance to paromomycin and to lesser extent tolerance to sorbic acid, but it has no detectable effect on resistance to 4-NQO. These observations suggest that the Sit4 protein phosphatase has a broad role in modulating multidrug resistance in K. lactis. Expression or activity of a membrane transporter specific for paromomycin and the ABC pumps responsible for 4-NQO and sorbic acid would be positively regulated by Sit4p. In contrast, the function of a Pdr5-type transporter responsible for ketoconazole and econazole extrusion, and probably also for efflux of oligomycin and antimycin, is likely to be negatively regulated by the phosphatase. Drug resistance of sit4 mutants was shown to be mediated by ABC transporters as efflux of the anionic fluorescent dye rhodamine 6G, a substrate for the Pdr5-type pump, is markedly increased in sit4 mutants in an energy-dependent and FK506-sensitive manner.

Topics: 4-Nitroquinoline-1-oxide; Antifungal Agents; Antimycin A; Drug Resistance, Multiple; Econazole; Genetic Complementation Test; Genotype; Ketoconazole; Kluyveromyces; Molecular Sequence Data; Oligomycins; Paromomycin; Phosphoprotein Phosphatases; Protein Phosphatase 2; Restriction Mapping; Saccharomyces cerevisiae Proteins; Sorbic Acid; Tacrolimus