O. V. Akopova
Ca2+-uptake accompanied with mitochondrial permeability transition pore (MPTP) opening is studied in rat liver mitochondria. In conditions of MPTP opening, as well as in conditions of MPTP blockage by cyclosporine A (CsA), Ca2+-uptake in mitochondria is counterbalanced by proton efflux into incubation medium. Independent of MPTP opening, observed stoichiometry of this exchange is 1Ca2+ : 1H+. MPTP opening dramatically decreases Ca2+-uptake in mitochondria: from ~400 nmol/mg protein in the presence of CsA to ~80?100 nmol/mg protein due to the increased mitochondrial membrane permeability. In the absence of CsA Ca2+-uptake is accompanied by the insensitive to Ca2+-uniporter blocker, ruthenium red (RR), release of Ca2+ from mitochondria which corresponds to as well RR-insensitive, but sensitive to CsA uptake of H+ into mitochondrial matrix. This calcium-proton exchange resulting from MPTP opening is observed only when Ca2+ uptake into matrix exceeds some basal level. The data are consistent with an assumption that, contrary to Ca2+-uniporter, MPTP has its own proton conductance. MPTP opening provides exchange of Ca2+ between mitochondria and medium which is coupled to the counterflow of protons into matrix space. Obtained data elucidate the physiological role of MPTP as regulatory mechanism for control of Ca2+-uptake level and intramitochondrial pH.
Key words: mitochondrial pore, Ca2+-uniporter, Ca2+, H+, transport, Ca2+-uptake.
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