Mitochondrial permeability transition (MPT) induced by the thiol cross-linker phenylarsine oxide (PhAsO) in Ca 2+ -depleted mitochondria incubated in the presence of ruthenium red, an inhibitor of the Ca 2+ uniporter, is stimulated by the addition of extramitochondrial Ca 2+ . The presence of extramitochondrial Ca 2+ stimulates the reaction of mitochondrial membrane protein thiol groups with PhAsO. Both Ca 2+ -induced increase in mitochondrial membrane permeabilization and protein thiol group reaction with PhAsO are dependent on time (5–10 min to be complete) and the concentration of Ca 2+ (1–25 μM). Mitochondrial permeabilization induced by PhAsO (15 μM) and extramitochondrial Ca 2+ is inhibited by ADP, cyclosporin A, dibucaine and Mg 2+ , while mitochondrial permeabilization induced by high concentrations of PhAsO (60 μM) in the absence of Ca 2+ is inhibited only by ADP and cyclosporin A. These results suggest that dibucaine and Mg 2+ can inhibit mitochondrial permeabilization by antagonizing the effect of Ca 2+ on the mitochondrial membrane. Once mitochondrial permeabilization induced by 15 μM PhAsO and extramitochondrial Ca 2+ has already occurred, the addition of the Ca 2+ chelator EGTA restores mitochondrial membrane potential (MPT pore closure), suggesting that the presence of Ca 2+ is essential for the maintenance of the permeability of the mitochondrial membrane to protons (MPT pore opening). In conclusion, the results presented indicate that low Ca 2+ concentrations acting at the external side of the inner mitochondrial membrane can stimulate mitochondrial permeability transition induced by PhAsO, due to increased accessibility of protein thiol groups to the reaction with PhAsO and increased probability of MPT pore opening.
Biochimica et Biophysica Acta (BBA) - Bioenergetics – Elsevier
Published: Dec 15, 1997
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