Effect of trifluoperazine on skeletal muscle mitochondrial respiration

The effect of trifluoperazine on the respiration of porcine liver and skeletal muscle mitochondria was investigated by polarographic and spectroscopic techniques. Low concentrations of trifluoperazine (88 nmol/mg protein) inhibited both the ADP- and Ca²⁺-stimulated oxidation of succinate, and reduced the values of the respiratory control index and the $\text{ADP}\text{O}$ and $\text{Ca}{}^{\mathrm{2+}}\text{O}$ ratio. High concentrations inhibited both succinate and ascorbate plus tetramethyl-p-phenylenediame (TMPD) oxidations, and uncoupler (carbonyl cyanide p-trifluromethoxyphenylhydrazone) and Ca²⁺-stimulated respiration. Porcine liver mitochondria were more sensitive to trifluoperazine than skeletal muscle mitochondria. Trifluoperazine inhibited the electron transport of succinate oxidation of skeletal muscle mitochondria within the cytochrome b-c₁ and cytochrome c₁-aa₃ segments of the respiratory chain system. 233 nmol trifluoperazine/mg protein inhibited the aerobic steady-state reduction of cytochrome c₁ by 92% with succinate as substrate, and of cytochrome c and cytochrome aa₃ by 50–60% with ascorbate plus TMPD as electron donors. Trifluoperazine can thus inhibit calmodulin-independent reactions particularly when used at high concentrations.     

Effect of hydrostatic pressure on halothane-induced depression of mitochondrial respiration

Anesthetized animals are awakened when subjected to increased atmospheric pressure. Whether all phenomena associated with the anesthetic state are similarly reversed is not known. Since the anesthetic halothane produces a dose-related reversible depression of rat liver mitochondrial respiration, the effect of 51 atmospheres of pressure on the drug's action was evaluated. It is concluded that application of pressure does not antagonize the inhibition produced by this anesthetic.     

Effect of photosynthesis on dark mitochondrial respiration in green cells

Green plant cells can generate ATP in both chloroplasts and mitochondria. Hence the effect of photosynthesis on dark mitochondrial respiration can be considered at a variety of levels. Turnover of ceitric acid cycle dehydrogenases, which is essential for supply of carbon skeletons for amino acid synthesis, seems to be largely unaffected during photosynthesis. The source of carbon for the anaplerotic function of the citric acid cycle in light is however, not known with certainty. NADH generated in these reactions is probably not oxidised via the mitochondrial electron transfer chain coupled to ATP synthesis. However, it may be oxidised by the alternative cyanide-insensitive pathway, exported to the cytosol via the oxaloacetate-malate dicarboxylate shuttle or directly utilised for cytosolic nitrate reduction. Oxidation of succinate via cytochrome oxidase may also be similarly inhibited in light. Whether increase in the cytosolic ATP/ADP ratio in light is responsible for the inhibition of mitochondrial electron transfer to O₂ is not clearly established, because the ATP/ADP ratio is reported to be already quite high in the dark. Effective collaboration between photophosphorylation and oxidative phosphorylation in order to maintain the cytosolic energy charge at a present high level is discussed.     

Effect of the outer mitochondrial membrane fraction on mitoplast respiration

Additions of the fraction of outer mitochondrial membranes to the mitoplast suspension is shown to bring about an increase of the ADP-stimulated respiration rate, indices of respiration control and uncoupled respiration. This effect is not a result of the cytochrome c presence in the fraction of outer membranes. In the glycerol-containing medium which causes dissociation of intermembrane contacts the coupling effect of outer membranes on mitoplast respiration is not revealed. It is concluded that the outer membrane in contact with the inner one takes part in realization of the mitochondrial coupling.     

Effect of hyperglycemia and hyperthermia on liver mitochondrial respiration and blood glucose content of rats during postnatal ontogenesis]

Correlation between glucose level in blood and liver mitochondrial energetics of 1, 10, 20-days rats under hyperglycemia and high environmental temperature (38 degrees C) has been studied. Glucose feeding led to a significant increase of glucose content in blood, this increase being less at hyperthermia. Glucose feeding strengthened the oxidation of such intermediates as succinate (Krebs cycle), pyruvate and malate (hydrocarbonates) and caprylate (lipid). High environmental temperature with hyperglycemia suppresses the liver mitochondria breathing, hydrocarbon and lipid intermediates being used; the suppression is less in the presence of succinate. It is found that liver mitochondria of growing rats at different experimental conditions oxidize different intermediates with various rates. These data can be explained in the light of ontogenetic evolution of the energetic apparatus. It is supposed that exogenic glucose is the factor which activates growing processes of animals and to certain extent diminishes the negative influence of hyperthermia on the organism.     

Control of mitochondrial respiration

The control theory of Kacser and Burns [in: Rate Control of Biological Processes (Davies, D.D. ed) pp. 65-104, Cambridge University Press, London, 1973] and Heinrich and Rapoport [Eur. J. Biochem. (1974) 42, 97-105] has been used to quantify the amount of control exerted by different steps on mitochondrial oxidative phosphorylation in rat-liver mitochondria. Inhibitors were used to manipulate the amount of active enzyme. The control strength of the adenine nucleotide translocator was measured by carrying out titrations with carboxyatractyloside. In state 4, the control strength of the translocator was found to be zero. As the rate of respiration was increased by adding hexokinase, the control strength of the translocator increased to a maximum value of approximately 30% at approximately 80% of state 3 respiration. In state 3, control of respiration is distributed between a number of steps, including the adenine nucleotide translocator, the dicarboxylate carrier and cytochrome c oxidase. The measured values for the distribution of control agree very well with those calculated with the aid of a model for mitochondrial oxidative phosphorylation developed by Bohnensack et al. [Biochim. Biophys. Acta (1982) 680, 271-280].     

Effect of ethanol intake on rat liver mitochondrial respiration and oxidative phosphorylation

The effect of ethanol intake on liver mitochondrial functions was investigated by feeding rats with a liquid isocaloric diet containing various concentrations of ethanol. We found that after feeding the liquid diet for 2 to 3 months, the body weight of rats did not show a significant difference between treated and control groups. However, the mitochondrial respiration rate decreased significantly with the increase of ethanol concentration in the diet. We found that when the rats were fed on 10.8% ethanol, the average succinate-supported State 3 respiration rate decreased from 54.5 to 44.8 nmol O2/min/mg and the glutamate-malate-supported State 3 respiration rate decreased from 38.8 to 23.6 nmol O2/min/mg as compared with the control. Interestingly, we noted that ethanol intake caused a more drastic effect on State 3 respiration than on State 4 respiration, irrespective of the substrate utilized by the mitochondria. In addition, the respiratory control and ADP/O ratios were found to decrease concomitantly with the increase of ethanol level in the diet. Moreover, we found that the effect of ethanol on both respiratory control and ADP/O ratios of liver mitochondria was more pronounced in glutamate-malate-supported respiration than succinate-supported respiration. These results clearly demonstrate that ethanol intake by the rat can cause impairment of liver mitochondrial respiration and oxidative phosphorylation, and that these effects are exerted through damage to mitochondrial membranes.     

Control of plant mitochondrial respiration

Plant mitochondria are characterised by the presence of both phosphorylating (cytochrome) and non-phosphorylating (alternative) respiratory pathways, the relative activities of which directly affect the efficiency of mitochondrial energy conservation. Different approaches to study the regulation of the partitioning of reducing equivalents between these routes are critically reviewed. Furthermore, an updated view is provided regarding the understanding of plant mitochondrial respiration in terms of metabolic control. We emphasise the extent to which kinetic modelling and 'top-down' metabolic control analysis improve the insight in phenomena related to plant mitochondrial respiration. This is illustrated with an example regarding the affinity of the plant alternative oxidase for oxygen.     

Age-related differences in the effect of osmotic pressure on liver mitochondrial respiration in rats]

The subject under investigation is the influence of osmotic pressure of incubation medium (25-500 mM of sucrose) upon the respiration and the respiration control (RC) of mitochondria of the liver of rats aged 1, 3, 12 and 24 months when oxidizing succinate. In a medium with 0.3 M of sucrose the respiration rate under condition 3 (V3) and RC increased from the age of 1 to 12 months and decreased by 24 months. In a medium with 0.15 M of sucrose the age differences have not been observed. In a uncoupling state the osmotic dependence of the respiration of mitochondria of 1- and 12-month-old rats did not vary. It is assumed that with age there is a change in the rate of structural coupling of the carrier of adenine nucleotides with H(+)-ATP synthetase complex and (or) the viscosity of the matrix.     

Inhibitory effects of Bcl-2 on mitochondrial respiration

In contrast to the well-established anti-apoptotic effect of Bcl-2 protein, we have recently demonstrated that Bcl-2 overexpression by vaccinia virus causes apoptosis in BSC-40 cells, while it prevents apoptosis in HeLa G cells. Given the key role of mitochondria in the process of apoptosis, we focused on effects of Bcl-2 expression on mitochondrial energetics of these two cell lines. In this study we present data indicating that BSC-40 cells derive their ATP mainly from oxidative phosphorylation whereas HeLa G cells from glycolysis. More importantly, we show that in both cell lines, Bcl-2 inhibits mitochondrial respiration and causes a decrease of the ATP/ADP ratio. However, it appears that BSC-40 cells cannot sustain this decrease and die, while HeLa G cells survive, being adapted to the low ratio of ATP/ADP maintained by glycolysis. Based on this observation, we propose that the outcome of Bcl-2 expression is determined by the type of cellular ATP synthesis, namely that Bcl-2 causes apoptosis in cells relying on oxidative phosphorylation.     

Effect of the aqueous extract of Hyptis pectinata on liver mitochondrial respiration

Some studies have indicated that mitochondria may be the target organelle of plants. We therefore decided to assess the effects of the aqueous extract of Hyptis pectinata leaves on liver mitochondrial respiratory function in vitro. Eight rat livers were subjected to isolation of mitochondria by differential centrifugation. In an adequate medium, the plant extract was added at different concentrations. The analyzed data were: state 3, state 4 and respiratory control ratio (RCR). H. pectinata extract caused a statistically significant decrease in state 3 (at 0.05, 0.1 and 0.2 mg/mg protein) and RCR (at 0.05, 0.1 and 0.2 mg/mg protein). Respiratory state 4 was not altered by the increasing concentrations. In conclusion, the aqueous extract of H. pectinata leaves may not injure the mitochondrial inner membrane but decreases significantly the oxidative phosphorylation.