Journal archive > 2008 > N 2 March-April
REVERSIBILITY OF ENERGY-DEPENDENT Са2+ ACCUMULATION IN MITOCHONDRIA
O. V. Akopova
Са2+ accumulation in energized rat liver mitochondria has been studied after the blockage of mitochondrial permeability transition pore (MPTP) by cyclosporin A. It is shown that Са2+ transport is coupled to the countertransport of protons: from the matrix of mitochondria in the medium in the course of Са2+ accumulation, and, on the contrary, from the medium to mitochondrial matrix after membrane depolarization. In standard incubation medium containing K+, Cl-, oxidation substrate (glutamate) and inorganic phosphate (H2PO4-) the observed stoichiometry of the exchange is 1Са2+?:?1H+. In accordance with this exchange ratio, proton, as well as cation, transport follows the same first-order kinetics, which is characterized in both cases by very close values of reaction half-times and rate constants. It is shown that reversion of Са2+-uniporter, sensitive to ruthenium red, is necessary for Са2+-efflux from the matrix of deenergized mitochondria when MPTP is blocked by cyclosporin A. It is also shown that Са2+-uniporter reversion takes place only after membrane depolarization and permeabilization by protonophore CCCP. Саlcium release from mitochondria in the presence of CCCP is accompanied by proton flow into the matrix. Both calcium and proton fluxes are sensitive to Са2+-uniporter blocker, ruthenium red, which gives the evidence of the identity of Са2+-efflux and influx pathways. The data obtained lead to the conclusion that calcium-proton exchange is necessary for Са2+-uniporter reversion and the reversibility of energy-dependent Са2+-uptake in mitochondria.
Key words: mitochondria, calcium, Ca2+-uniporter, proton, transport, protonophore.
The original article in Russian is available for download in PDF format.
© The Ukrainian Biochemical Journal