[EFFECT OF CURCUMIN ON MITOCHONDRIAL FUNCTION OF CARDIOMYOCYTES WITH DOXORUBICIN-INDUCED OXIDATIVE STRESS].

We studied the effect of curcumin on the cardiomyocytes viability, processes of oxidative phosphorylation in the mitochondria of cardiomyocytes, their pro- and antioxidant balance in doxorubicin-induced oxidative stress. It has been revealed that administration of doxorubicin to rats led to a significant increase in the secondary products of lipid peroxidation (TBARS) in mitochondria by 21 and H(2)0(2) by 76%, reduction of the enzymatic activity of mitochondrial Mn-SOD by 14% and intensified catalase activity by 80% compared with the control. After combined use of doxorubicin and curcumin the content of TBARS and H(2)0(2) increased by 14 and 26%, respectively, the enzymatic activity of catalase decreased by 28%, and mitochondrial Mn-SOD activity intensified by 9%. During the incubation with doxorubicin, the number of live cells decreased by 30.4% and the number of necrotic cells increased by 30.4% relative to control. Coadministration of doxorubicin and curcumin led to augmented cell viability by 8%, while the number of necrotic cells reduced by 8% compared with the use of doxorubicin only. In assessing the parameters of mitochondrial respiration in rats that received injections of doxorubicin active breathing index (V(3)) fell by 43.8%, the oxidation rate of the contingency of phosphorylation (V(3)/V(4)(ATp)) decreased by 47% and phosphorylation efficiency index (ADP/O) also declined by 31.7% respectively compared with the control. The combined use of doxorubicin and curcumin improved the indicators of mitochondrial respiration compared to using only doxorubicin: V(3) raised by 25%, V(3)/V(4)(ATP)by 18% and ADP/O by 12% respectively.

siRNA-induced silencing of hypoxia-inducible factor 3α (HIF3α) increases endurance capacity in rats.

Molecular mechanisms of adaptation to exercise despite a large number of studies remain unclear. One of the crucial factors in this process is hypoxia inducible factor (HIF) that regulates transcription of many target genes encoding proteins that are implicated in molecular adaptation to hypoxia. Experiments were conducted on 24 adult male Fisher rats. Real-time PCR analysis was performed for quantitative evaluation of Hif3α, Igf1, Glut-4 and Pdk-1 in m. gastrocnemius, m. soleus, in lung and heart tissues. Mitochondrial respiratory function and electron microscopy were performed. Knockdown of Hif3α using siRNA increases time of swimming to exhaustion by 1.5 times. Level of mitochondrial NAD- and FAD-dependent oxidative pathways is decreased, however efficiency of phosphorylation is increased after Hif3α siRNA treatment. Expression of HIF target genes in muscles was not changed significantly, except for increasing of Pdk-1 expression in m. soleus by 2.1 times. More prominent changes were estimated in lung and heart: Igf1 gene expression was increased by 32.5 and 37.5 times correspondingly. Glut4 gene expression in lungs was increased from undetected level till 0.3 rel. units and by 84.2 times in heart. Level of Pdk1 gene expression was increased by 249.2 in lungs and by 35.1 times in hearts, correspondingly. Some destructive changes in muscle tissue were detected in animals with siRNA-inducing silencing of Hif3α.

[ENERGETIC AND ANTIOXIDANT STATUS OF RAT LIVER MITOCHONDRIA DURING HYPOXIA-REOXYGENATION OF DIFFERENT DURATION].

Dynamics of changes in activity and protein expression of antiradical (MnSOD), glutathione-dependent (glutathione peroxidase, glutathione reductase) and NADP⁺-generated (isocitrate dehydrogenase) enzymes as well as in the energy metabolism indeces in rat liver mitochondria under hypoxia- reoxygenation of different duration (1, 3, 7 14 days) were studied. Prolonged hypoxia-reoxygenation was characterized by phase changes of the corticosterone concentration in rat blood, which corresponded to the changes in energy metabolism as well as in pro- and antioxidant balance in rat liver mitochondria. It has been shown that short-term (1 day) hypoxia-reoxygenation (5% O2 in the gas mixture) led to an increase in the blood corticosterone concentration and a significant activation of oxidative processes and energy metabolism in rat liver mitochondria, the intensity of which was reduced to 3rd day. Long- term hypoxia--reoxygenation (7-14th days) led to the gradual depletion of the organism adaptive capabilities, as evidenced by a significant decline in the blood corticosterone concentration, an increase in the content of secondary products of lipid peroxidation, an imbalance in pro- and antioxidant reactions and reduction of energy capacity in liver cells mitochondria. It has been shown that the glutathione peroxidase protein expression and enzymatic activity increased constantly during the whole experimental period and correlated positively with the level of H2O2. The amount of Mn-SOD protein as well as it's enzymatic activity was lower in the first seven days of experiment, and it was increased in consequent days up to the control level on 14thday. Increased activity of glutathione peroxidase, glutathione reductase and NADP+⁺dependent isocitrate dehydrogenase during prolonged hypoxia - eoxygenation indicates that glutathione- and NADPH-generating enzymes, were actively involved in the antioxidant protect.

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

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.

[The effect of ATP-dependent K(+)-channel opener on transmembrane potassium exchange and reactive oxygen species production upon the opening of mitochondrial pore].

The effect of mitochondrial ATP-dependent K(+)-channel (K(+)ATP-channel) opener diazoxide (DZ) on transmembrane potassium exchange and reactive oxygen species (ROS) formation under the opening of mitochondrial permeability transition pore (MPTP) was studied in rat liver mitochondria. The activation of K(+)-cycling (K(+)-uptake and K(+)/H(+)-exchange) by DZ was established with peak effect at < or = 500 nM. It was shown that MPTP opening as well resulted in the activation of K(+)-cycling together with simultaneous activation of Ca(2+)-cycle in mitochondria. In the absence of depolarization Ca(2+)-cycle is supported by MPTP and Ca(2+)-uniporter. The stimulation of K(+)/H(+)-exchange by MPTP opening led to the activation of K(+)-cycle, but further activation of K(+)/H(+)-exchange resulted in MPTP inhibition. Under the same conditions the decrease in mitochondrial ROS production was observed. It was proposed that the decrease in ROS formation together with K(+)/H(+)-exchange activation could be the constituents of the complex effect of MPTP inhibition induced by K(+)ATP-channel opener.

Effect of potential-dependent potassium uptake on production of reactive oxygen species in rat brain mitochondria.

The effect of potential-dependent potassium uptake on reactive oxygen species (ROS) generation in mitochondria of rat brain was studied. It was found that the effect of K+ uptake on ROS production in the brain mitochondria under steady-state conditions (state 4) was determined by potassium-dependent changes in the membrane potential of the mitochondria (ΔΨm). At K+ concentrations within the range of 0-120 mM, an increase in the initial rate of K(+)-uptake into the matrix resulted in a decrease in the steady-state rate of ROS generation due to the K(+)-induced depolarization of the mitochondrial membrane. The selective blockage of the ATP-dependent potassium channel (K(ATP)(+)-channel) by glibenclamide and 5-hydroxydecanoate resulted in an increase in ROS production due to the membrane repolarization caused by partial inhibition of the potential-dependent K+ uptake. The ATP-dependent transport of K+ was shown to be ~40% of the potential-dependent K+ uptake in the brain mitochondria. Based on the findings of the experiments, the potential-dependent transport of K+ was concluded to be a physiologically important regulator of ROS generation in the brain mitochondria and that the functional activity of the native K(ATP)(+)-channel in these organelles under physiological conditions can be an effective tool for preventing ROS overproduction in brain neurons.

[The effect of uridine on the endurance of animals with different resistance to physical stress: the role of mitochondrial ATP-dependent potassium channel].

The effect of a metabolic precursor of natural activator of mitochondrial ATP-dependent potassium channel (mitochondrial K+(ATP))--uridine on animal's endurance to physical stress was studied. The endurance was determined by recording the time period during which the rat loaded with a plummet of 20% of body weight can swim until physical exhaustion at 32 degrees C. It was found that highly resistant animals swam until exhaustion for 7.40 ± 0.35 min, whereas low resistant rats hold out 2.07 ± 0.10 min only. The injection of uridine influenced the swimming time of the animals, increasing it twofold in low-resistant rats. The effect of uridine was decreased by injection of inhibitors of mitochondrial K+(ATP) channel. It was found that the injection of uridine into low resistant rats increased the rate of potassium transport in mitochondria isolated from liver of these rats, and inhibitors of the channel prevent the channel activating effect of uridine. The role of mitochondrial K+(ATP) cannel in the formation of animal's resistance to physical stress and protection of tissues from hypoxia is discussed.

[Phase changes of energy metabolism during adaptation to immobilization stress].

In stress, it was showed the organ and tissue changes associated with damage by lipid peroxides, and the disrupted barrier function. As a consequence, it was to lead to a syndrome of "stress-induced lung" and violation of oxygen delivery to the tissues and hypoxia. Purpose of the study was to investigate the dynamics of changes in gas exchange, blood glucose, body temperature, oxidant and antioxidant system activity, as well as mitochondrial respiration by Chance under the influence of chronic stress (6-hour immobilization daily for 3 weeks). It was identified 4 phase changes of energy metabolism in the dynamics of chronic stress. In the first phase, hypomethabolic, instability oxidative metabolism, decreased oxidation of NAD-dependent substrates, significant elevation of FAD-dependent substrates oxidation and low MRU were found. The activity of superoxide dismutase (MnSOD) was increased; it was occurred on a background low activity of glutathione peroxidase, and of misbalanced antioxidant system. After seven immobilizations, second phase-shift in energy metabolism, was observed, and then the third phase (hypermetabolic) started. It was characterized by gradual increase in oxidative metabolism, the restoration of oxidation of NAD-dependent substrates, MRU, as well as optimizing balance of oxidant and antioxidant systems. The fourth phase was started after 15 immobilizations, and characterized by the development of adaptive reactions expressed in increased tolerance of energy metabolism to the impact of immobilization. The results are correlated with changes in the dynamics of blood corticosterone. Thus, it was found the phase character of the energy metabolism rebuilding during the chronic stress.

[Pharmacological correction of experimental mitochondrial dysfunction of brain stem neurons by rhytmocor and mildronate].

The results of pharmacological correction of experimental mitochondrial dysfunction in brain stem neurons after single injection of specific respiratory complex I inhibitor rotenone by complex agents mildronate and rhytmocor have been presented. It was shown that 14-days rhytmocor injection promoted the rise of mitochondrial reserve capacity under glutamate and malate oxidation as well as under succinate oxidation. The mildronate injection was accompanied by enhancement of the velocity of phosphorilated mitochondrial respiration in the presence and absence of ADP when both substrates of oxidation were used. Under the brain stem experimental mitochondrial dysfunction, mildronate improved a decreased velocity of phosphorilated mitochondrial respiration and the respiratory control in a more significant degree under glutamate malate as the substrates of oxidation. Simultaneous increase in the respiratory control and in the coefficient of efficacy ofphosphorilation during the correction of experimental mitochondrial dysfunction by rhytmocor could suggest about essential economization of processes in mitochondrial respiratory chain. It was concluded that the main mechanisms of influence on mitochondrial disturbances of both agents were connected to the powerful rise of NAD-related oxidation which allowed to enhance a resistance of mitochondrial respiratory chain and to optimize the mitochondrial function.

[The effect of ATP-dependent K(+)-channel opener on the functional state and the opening of cyclosporine-sensitive pore in rat liver mitochondria].

The effect of mitochondrial ATP-dependent K(+)-channel (K+(ATP)-channel) opener diazoxide (DZ) on the oxygen consumption, functional state and the opening of cyclosporine-sensitive pore in the rat liver mitochondria has been studied. It has been established that K+(ATP)-channel activation results in the increase of the oxygen consumption rate (V4(s)) and the uncoupling due to the acceleration of K(+)-cycling, the decrease in state 3 respiration rate (V3) and the respiratory control ratio (RCR). Under K+(ATP)-channel activation an inhibition of oxidative phosphorylation takes place which reduces the rate of ATP synthesis and hydrolysis as well as ATP production and consequently results in the seeming increase of P/O ratio. It has been shown that the increase in ATP-dependent K(+)-uptake accompanied by the opening of mitochondrial permeability transition pore (MPTP) leads to dramatic uncoupling of the respiratory chain due to simultaneous activation of K(+)- and Ca(2+)-cycling supported by MPTP and Ca(2+)-uniporter as well as K(+)-channels and K+/H(+)-exchange. K+(ATP)-channel activation leads to the partial inhibition of MPTP, but insufficient for the restoration of mitochondrial functions. Elimination of Ca(2+)-cycling after MPTP opening is necessary to return mitochondrial functions back to the control level which shows that MPTP could serve as the mechanism of reversible modulation of bioenergetic effects of K+(ATP)-channel activation.

[Disturbances of oxygen-dependent processes in periodontal tissues under prolonged immobilization stress and ways of their pharmacological correction].

Influence of prolonged immobilization (6 h strict horizontal position of rats in the tight containers daily for 2 weeks) on oxygen tension, oxygen consumption, pro-/antioxidant balance, and energetic metabolism of soft and hard periodontal tissues has been investigated. It was established that prolonged immobilization stress resulted in marked decrease in the gum tissue PO2 (36%) and in the bone tissue oxygen consumption rate (46%) compared to control. It was also determined that prolonged stress led to a reduction in the gum mitochondrial respiration rate. The latter was more expressed in case of the NAD-dependent substrate oxidation than of the FAD- dependent one. It was determined that the prolonged stress results in intensification of peroxide processes and depletion of antioxidant protection of soft tissues of periodontum. It was found that Thiotriazolin and Actovegin have modified and diminished stress-induced disorders in the soft and hard periodontal tissues oxygen homeostasis under prolonged immobilization stress.

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

The effect of potential-dependent potassium uptake on the transmembrane potential difference (DeltaPsi(m)) 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 approximately 35% of potential-dependent potassium uptake in the brain mitochondria. It was shown that K+(ATP)-channel blockage results in membrane repolarization by approximately 20% of control, which is consistent with experimental dependence of DeltaPsi(m) 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.

Effect of potential-dependent potassium uptake on calcium accumulation in rat brain mitochondria.

The effect of potential-dependent potassium uptake at 0-120 mM K+ on matrix Ca2+ accumulation in rat brain mitochondria was studied. An increase in oxygen consumption and proton extrusion rates as well as increase in matrix pH with increase in K+ content in the medium was observed due to K+ uptake into the mitochondria. The accumulation of Ca2+ was shown to depend on K+ concentration in the medium. At K+ concentration ≤30 mM, Ca2+ uptake is decreased due to K+-induced membrane depolarization, whereas at higher K+ concentrations, up to 120 mM K+, Ca2+ uptake is increased in spite of membrane depolarization caused by matrix alkalization due to K+ uptake. Mitochondrial K+(ATP)-channel blockers (glibenclamide and 5-hydroxydecanoic acid) diminish K+ uptake as well as K+-induced depolarization and matrix alkalization, which results in attenuation of the potassium-induced effects on matrix Ca2+ uptake, i.e. increase in Ca2+ uptake at low K+ content in the medium due to the smaller membrane depolarization and decrease in Ca2+ uptake at high potassium concentrations because of restricted rise in matrix pH. The results show the importance of potential-dependent potassium uptake, and especially the K+(ATP) channel, in the regulation of calcium accumulation in rat brain mitochondria.

[The effect of Ca(2+)-induced opening of cyclosporine-sensitive pore on the oxygen consumption and functional state of rat liver mitochondria].

The effect of Ca(2+)-induced opening of cyclosporine-sensitive pore (mitochondrial permeability transition pore, MPTP) on the oxygen consumption and mitochondrial functional state was studied in the rat liver mitochondria. It was shown that, with the use of glutamate as oxidation substrate, in the absence of depolarization MPTP opening results in the increase of steady state respiration rate because of the activation of cyclosporine-sensitive Ca2+/H(+)-exchange and Ca2+ cycling, which was supported by the simultaneous work of MPTP and Ca(2+)-uniporter. With the aid of selective blockers, cyclosporine A and ruthenium red, it was shown that MPTP and Ca(2+)-uniporter contribute equally to the Ca(2+)-cycling and mitochondrial respiration. It was shown that bioenergetic effects of MPTP opening under steady state conditions (increase in the oxygen consumption rate under substrate oxidation without ADP, decrease in respiratory control ratio as well as the effectiveness of ATP synthesis, P/O) are close to the functional alterations, which result from the increase of endogenous proton conductance of mitochondrial membrane. Uncoupling effect of MPTP opening, by itself, had no effect on phosphorylation rate, which remains relatively stable because the fall of P/O is compensated by the activation of respiratory chain and the increase in the rate of state 3 respiration. It was concluded that under physiologically normal conditions MPTP might function as the endogenous mechanism of mild uncoupling of respiratory chain.

[Continuous adaptation of rats to hypobaric hypoxia prevents stressor hyperglycemia and optimizes mitochondrial respiration under acute hypoxia].

Oxygen consumption, glucose blood level and liver mitochondrial respiration were investigated in male Wistar rats permanently living in middle altitude (2100 m, Elbrus region). The animals were characterized by reduced body oxygen consumption and blood glucose level, as well as by intensified utilization of NAD-dependent substrates in mitochondrial respiratory chain with increasing indices of ADP-stimulated respiration in comparison with plains rats. As a result of adaptive rebuilding of oxidative metabolism in rats--inhabitants of midlands, the nature and severity of metabolic responses to acute hypoxia were also changed. After lifting in barochamber to a "height" of 5600 m during 3 hours, plains rats transiently demonstrated hypometabolic and hyperglycemic reactions. A rapid adaptation of mitochondrial function occurred due to increase in the rate of FAD-dependent substrate oxidation accompanied by a decrease in the effectiveness of phosphorylation. In midland rats, by contrast, hypoglycemic reaction was developed, and further reduction of aerobic metabolism was limited. Rapid adaptation of mitochondrial function to acute hypoxia in those rats was more intense than in the plains animals. This was achieved by a significant increase in the rate of NAD-dependent substrate oxidation, especially lipids, and an improved efficiency of mitochondrial respiration and an increased economy of oxygen utilization.

[Phase changes in energy metabolism during periodic hypoxia].

Male Wistar rats were exposed to periodic hypobaric hypoxia (PHH), by "lifting" in barochamber at "altitude" 5600 m for 1 h every 3 days (6 séances). The dynamics of changes in oxygen consumption (VO2), and body temperature (Tm), as well as in HIF-1alpha and HIF-3alpha gene expression, and mitochondrial respiration in the ventricles of the heart was studied. On the basis of the data we identified four phases of the physiological changes. The first phase, hypometabolic (1-3 séances), is characterized by decrease in VO2 and Tm, induction of HIF-1alpha and HIF-3alpha with delayed transient stimulation of metabolism in response to each séance of hypoxia. In heart mitochondria, V3 and V4 are increased, but V3/V4 and ADP/O are reduced. During the second phase, transitional (3-4 séances), there is reorganization of metabolism and decrease its hypoxic reactivity. The third phase, hypermetabolic (4-5 séances), is characterized by intensification of metabolism and compensation of hypoxic disorders. The fourth phase (after 5 séance) - is a state of metabolic adaptation with normalization of VO2 and Tm, expression of HIF-1alpha and HIF-3alpha, mitochondrial respiration, increased NAD-dependent oxidation of carbohydrate and lipid substrates. Thus, during PHH consequent rebuilding of processes of oxygen transport, tissue respiration and thermogenesis occurs, mediated by induction of the HIF subunits.

HIF-3α mRNA expression changes in different tissues and their role in adaptation to intermittent hypoxia and physical exercise.

The role of HIF-3α in response to intermittent hypoxia and physical exercise was investigated in Fisher rats using reverse transcription, real-time PCR and RNA interference. Under acute hypoxia (12% O(2), 2h), the level of HIF-1α, HIF-2α, and HIF-1ß mRNA did not significantly change in the heart, lung, kidney and muscle tissues, but HIF-3α mRNA expression was strongly elevated in all tissues investigated. Five weeks of intermittent hypoxic training (IHT) led to an increase of HIF-3α mRNA in all studied tissues, but under the influence of acute hypoxia after IHT, the expression of HIF-3α mRNA did not increase in all tissues excluding skeletal muscle. Thus, IHT reduced the effect of acute hypoxia on HIF-3α mRNA expression in the heart, lung, and kidney. The expression of HIF-3α in skeletal muscle at endurance (swimming) training (ET) in combination with IHT was 6.2 times lower compared to the group with ET but without IHT and 3.3 times lower (P<0.05) compared to untrained control. After swimming training with IHT, rats demonstrated the highest level of physical endurance. RNA interference of HIF-3α significantly decreased the level of HIF-3α mRNA in both muscles investigated: by 2.6 times in m. soleus (P<0.03) and by 2.1 times in m. gastrocnemius (P<0.05) and elevated the physical endurance of rats by 50% (P<0.05) compared to control. Thus, the HIF-3α subunit is an essential member of hypoxic response. It plays a negative role in the adaptation to hypoxia, because the inhibition of HIF-3α expression leads to an increase in physical endurance.

Cytochrome C as an amplifier of ROS release in mitochondria.

The influence of exogenous cytochrome c on reactive oxygen species (ROS) formation and its dependence on mitochondrial permeability transition pore (MPTP) opening is studied in rat liver mitochondria. Fluorescent probe dichlorofluorescein (DCF) was used. It was shown that MPTP activation by increasing concentrations of Ca2+ in the medium results in the increase in mitochondrial ROS production and oxygen consumption, but the decrease in matrix calcium retention, dependent on the amount of added Ca2+. Cytochrome c in the incubation medium does not much influence ROS formation when MPTP opening is blocked by cyclosporine A. However, in the presence of cytochrome c MPTP opening is accompanied by dramatic increase in ROS production. Steep rise in DCF fluorescence because of matrix ROS formation is sensitive to MPTP opening and is not resulted from the direct interaction between the probe and cytochrome c outside the mitochondria. To explain obtained data the hypothesis is put forward that MPTP could serve for ROS exchange between the matrix and the medium where heme iron of cytochrome c would act as a catalytic center to enhance ROS production. We suppose that apart of its conventional function, cytochrome c which is not involved in electron transport, could serve in such way as the amplifier of ROS production which in turn would provide a background for the development of apoptosis due to MPTP opening.

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

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.

Influence of ATP-dependent K(+)-channel opener on K(+)-cycle and oxygen consumption in rat liver mitochondria.

The influence of the K+(ATP)-channel opener diazoxide on the K+ cycle and oxygen consumption has been studied in rat liver mitochondria. It was found that diazoxide activates the K+(ATP)-channel in the range of nanomolar concentrations (50-300 nM, K(1/2) ~ 140 nM), which results in activation of K+/H+ exchange in mitochondria. The latter, in turn, accelerates mitochondrial respiration in respiratory state 2. The contribution of K+(ATP)-channel to the mitochondrial potassium cycle was estimated using the selective K+(ATP)-channel blocker glibenclamide. The data show that the relative contribution of K+(ATP)-channel in the potassium cycle of mitochondria is variable and increases only with the decrease in the ATP-independent component of K+ uptake. Possible mechanisms underlying the observed phenomena are discussed. The experimental results more fully elucidate the role of K+(ATP)-channel in the regulation of mitochondrial functions, especially under pathological conditions accompanied by impairment of the mitochondrial energy state.