Tag Archives: brain mitochondria

The effect of permeability transition pore opening on reactive oxygen species production in rat brain mitochondria

O. V. Akopova, L. I. Kolchinskaya, V. I. Nosar, A. N. Smirnov, M. K. Malysheva, I. N. Mankovska, V. F. Sagach

Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv;
e-mail: luko@biph.kiev.ua

The influence of mitochondrial permeability transition pore (MPTP) opening on reactive oxygen species (ROS) production in the rat brain mitochondria was studied. It was shown that ROS production is regulated differently by the rate of oxygen consumption and membrane potential, dependent on steady-state or non-equilibrium conditions. Under steady-state conditions, at constant rate of Ca2+-cycling and oxygen consumption, ROS production is potential-dependent and decreases with the inhibition of respiration and mitochondrial depolarization. The constant rate of ROS release is in accord with proportional dependence of the rate of ROS formation on that of oxygen consumption. On the contrary, transition to non-equilibrium state, due to the release of cytochrome c from mitochondria and progressive respiration inhibition, results in the loss of proportionality in the rate of ROS production on the rate of respiration and an exponential rise of ROS production with time, independent of membrane potential. Independent of steady-state or non-equilibrium conditions, the rate of ROS formation is controlled by the rate of potential-dependent uptake of Ca2+ which is the rate-limiting step in ROS production. It was shown that MPTP opening differently regulates ROS production, dependent on Ca2+ concentration. At low calcium MPTP opening results in the decrease in ROS production because of partial mitochondrial depolarization, in spite of sustained increase in oxygen consumption rate by a cyclosporine A-sensitive component due to simultaneous work of Ca2+-uniporter and MPTP as Ca2+-influx and efflux pathways. The effect of MPTP opening at low Ca2+ concentrations is similar to that of Ca2+-ionophore, A-23187. At high calcium MPTP opening results in the increase of ROS release due to the rapid transition to non-equilibrium state because of cytochrome c loss and progressive gating of electron flow in respiratory chain. Thus, under physiological conditions MPTP opening at low intracellular calcium could attenuate oxidative damage and the impairment of neuronal functions by diminishing ROS formation in mitochondria.

The effect of potential-dependent potassium uptake on membrane potential in rat brain mitochondria

O. V. Akopova, V. I. Nosar, L. I. Kolchinskaya,
I. N. Mankovska, M. K. Malysheva, V. F. Sagach

Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv;
e-mail: luko@biph.kiev.ua

The effect of potential-dependent potassium uptake on the transmembrane potential difference (ΔΨm) in rat brain mitochondria has been studied­. It was shown that in potassium concentration range of 0-120 mM the potential-dependent K+-uptake into matrix leads to the increase in respiration rate and mitochondrial depolarization. ATP-dependent potassium channel (K+ATP-channel) blockers, gliben­clamide and 5-hydroxydecanoate, block ~35% of potential-dependent potassium uptake in the brain mitochondria. It was shown that K+ATP-channel blockage results in membrane repolarization by ~20% of control, which is consistent with experimental dependence of ΔΨm on the rate of potential-dependent potassium uptake. Obtained experimental data give the evidence that functional activity of K+ATP-channel is physiologically important in the regulation of membrane potential and energy-dependent processes in brain mitochondria.

Estimation of ATP-dependent K(+)-channel contribution to potential-dependent potassium uptake in the rat brain mitochondria

O. V. Akopova, V. I. Nosar, L. I. Kolchinskaya, I. N. Mankovska, V. F. Sagach

Bogomoletz Institute of  Physiology, National Academy of Sciences of Ukraine, Kyiv;
e-mail: a-dubensky@mail.ru

The effect of potassium on state 4 respiration (substrate oxidation in the absence of ADP) was investigated. It was shown that potential-dependent potassium uptake in the brain mitochondria results in mitochondrial depolarization. Taking into account depolarization effect of potassium, the contribution of the endo­genous proton leak as well as K+-uptake to the re­spiration rate was calculated. It was shown that such estimation allows the share of ATP-dependent potassium channel contribution to potential-dependent potassium uptake to be determined by polarographic method.