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PubMed2001

Restoration of Ca2+-inhibited oxidative phosphorylation in cardiac mitochondria by mitochondrial Ca2+ unloading.

Mitochondria, the major source of cellular ATP, display high vulnerability to metabolic stress, in particular to excessive Ca2+ loading. Here, we show that Ca2+-inhibited mitochondrial ATP generation could be restored through stimulated Ca2+ discharge from mitochondrial matrix. This was demonstrated using a Ca2+ ionophore or through Na+/Ca2+ exchange-mediated decrease of mitochondrial Ca2+ load. Furthermore, diazoxide, a mitochondrial potassium channel opener, which maintained mitochondrial Ca2+ homeostasis, also restored Ca2+-inhibited ATP synthesis and preserved the structural integrity of Ca2+-challenged mitochondria. Thus, under conditions of excessive mitochondrial Ca2+ overload targeting mitochondrial Ca2+ transport pathways restores oxidative phosphorylation required for vital cellular processes. This study, therefore, identifies an effective strategy capable to rescue Ca2+-disrupted mitochondrial energetics.

Adenosine Triphosphate↗
PubMedDate not supplied

[The effect of the new nonsteroidal anti-inflammatory agent glucamine on oxidative phosphorylation processes].

A study was made of the action of the nonsteroidal antiinflammatory agent glucamin on the processes of oxidation and phosphorylation (OP) in isolated mitochondria of the liver. It has been established that glucamin does not exhibit the properties of a separator in the explored concentrations (10(-2)-10(-7) M). Unlike the standard drug voltaren that separates OP processes, it slightly enhances interaction of liver mitochondria which oxidize NAD-dependent substrates. The effect of voltaren is dose-dependent, being pronounced to a greater measure when succinate is applied as a substrate of mitochondria oxidation.

Animals↗
PubMed1981

Oxidative Phosphorylation in Germinating Lettuce Seeds (Lactuca sativa) during the First Hours of Imbibition.

Experiments with lettuce seeds during the first hours of imbibition showed that oxygen is necessary to sustain high adenine nucleotide ratios and consequently, energy charge values are higher than 0.8 as is usually the case in normally metabolizing tissues.The energy charge value (0.2) of dry seeds soaked in aerated water increased to normal values (0.8) within 30 minutes. The energy charge value of seeds imbibed under cyanide or nitrogen stayed at low values, about 0.3 for 30 minutes. Nitrogen and cyanide treatment of seeds imbibed in aerated water produced a decrease of energy charge to low values within 3 minutes. During the first minutes of imbibition, the oxygen uptake is cyanide-sensitive. The effect of the uncoupler carbonyl cyanide p-trifluoromethoxyphenyl hydrazone was not as clear-cut. However, results were obtained which agree with the occurrence of oxidative phosphorylation during the first hours of imbibition. These results indicate that a normal cytochromic pathway synthesizes ATP during the first minutes and hours following the imbibition of lettuce seeds.

Journal Article↗
PubMed1983

The analysis of drug action on mitochondrial oxidative phosphorylation. The choice of organic solvent for water-insoluble drugs.

Four organic solvents were tested for their ability to interfere with ADP- and 2,4-dinitrophenol-stimulated respiration in tightly-coupled guinea-pig liver mitochondria. All four compounds inhibited mitochondrial respiration, but dimethylformamide and ethanol were more potent than dimethylsulphoxide and propyleneglycol. The latter compound was the only one that failed to produce a significant inhibition of the reactions. Using dimethylformamide, it was shown that inhibition of the reactions was independent of the substrates employed. A detailed analysis was made of the effect of a range of concentrations of dimethylformamide on the uncoupling activity of a range of concentrations of 2,4-dinitrophenol. It was clearly demonstrated that the inclusion of dimethylformamide in the reaction medium would result in an underestimate of the activity of dinitrophenol. Recommendations are made concerning the precautions that should be taken when analysing the effects of water-insoluble drugs on oxidative phosphorylation.

2,4-Dinitrophenol↗
PubMed1994

Characteristics of mitochondrial proton leak and control of oxidative phosphorylation in the major oxygen-consuming tissues of the rat.

Maintenance of an electrochemical proton gradient across the mitochondrial inner membrane against the significant proton permeability of the membrane accounts for 25-30% of resting oxygen consumption in hepatocytes. It has been proposed that proton leak could be a significant contributor to resting metabolic rate in mammals if it were present in other tissues. Mitochondria were isolated from the major oxygen-consuming tissues (liver, kidney, brain and skeletal muscle) of the rat. In each tissue, the mitochondria showed significant proton leak with the same characteristic non-linear dependence on membrane potential. Liver and kidney mitochondria showed similar membrane proton permeability per mg of mitochondrial protein; brain and muscle permeabilities were greater when expressed in this way. Differences in the kinetic response of the substrate oxidation and phosphorylating systems to membrane potential were observed. The substrate oxidation system was more active in kidney, brain and skeletal muscle mitochondria than in liver mitochondria per mg of mitochondrial protein. Liver and kidney phosphorylating systems were less active than brain and skeletal muscle per mg of mitochondrial protein. The control of oxidative phosphorylation was also assessed. The distribution of control in mitochondria isolated from the four tissue types was found to be similar.

Animals↗
PubMed2004

Senescence-associated changes in respiration and oxidative phosphorylation in primary human fibroblasts.

Limitation of lifespan in replicative senescence is related to oxidative stress, which is probably both the cause and consequence of impaired mitochondrial respiratory function. The respiration of senescent human diploid fibroblasts was analysed by high-resolution respirometry. To rule out cell-cycle effects, proliferating and growth-arrested young fibroblasts were used as controls. Uncoupled respiration, as normalized to citrate synthase activity, remained unchanged, reflecting a constant capacity of the respiratory chain. Oligomycin-inhibited respiration, however, was significantly increased in mitochondria of senescent cells, indicating a lower coupling of electron transport with phosphorylation. In contrast, growth-arrested young fibroblasts exhibited a higher coupling state compared with proliferating controls. In intact cells, partial uncoupling may lead to either decreased oxidative ATP production or a compensatory increase in routine respiration. To distinguish between these alternatives, we subtracted oligomycin-inhibited respiration from routine respiration, which allowed us to determine the part of respiratory activity coupled with ATP production. Despite substantial differences in the respiratory control ratio, ranging from 4 to 11 in the different experimental groups, a fixed proportion of respiratory capacity was maintained for coupled oxidative phosphorylation in all the experimental groups. This finding indicates that the senescent cells fully compensate for increased proton leakage by enhanced electron-transport activity in the routine state. These results provide a new insight into age-associated defects in mitochondrial function and compensatory mechanisms in intact cells.

Aging↗
PubMed1967

Tissue Respiration and Mitochondrial Oxidative Phosphorylation of NaCl-Treated Pea Seedlings.

The effect of sodium chloride added to root medium of pea seedlings on respiratory activity of tissue segments and on isolated mitochondria was studied. Salinization enhances the respiration of leaves about one-third on a fresh weight, dry weight or protein basis. Roots and stems show only 10 to 15% respiratory stimulation. The onset of respiratory increase in leaves roughly parallels the increase in NaCl content and the decrease in growth rate. At a later stage the elevated respiration is apparent in treated plants even though the concentration of NaCl reaches a plateau and osmotic adjustment is being reached. Stimulation of respiration was found in both etiolated and green plants. Experiments with DNP show that simple uncoupling by salt is not involved; the respiratory increase in control and treated tissue is proportionally the same.In accordance with increased respiration rates observed in vivo, mitochondria from salt-treated plants show higher rates of oxygen uptake on several substrates. The effect of NaCl added during growth is long term and is distinct from the effect of NaCl added to mitochondria isolated from control plants. Since P/O ratios are not affected by NaCl, the potential for oxidative phosphorylation in salt-affected tissue appears to increase. It is postulated that this increase may lead to changes in ADP and ATP content, and in turn, affect regulation of metabolic pathways.

Journal Article↗
PubMed1979

Uncouplers of oxidative phosphorylation promote derepression of the hexose transport system in cultures of hamster cells.

Long-term (18-24 hr) preincubation of NIL hamster cell cultures with D-glucose or D-glucosamine (both of which repress the hexose transport system) gave rise to a striking loss of the hexose transport system ("super-repression") when cycloheximide was also present in the culture medium. However, if 0.2 mM 2,4-dinitrophenol (DNP) was also present, the cycloheximide-mediated super-repression was prevented. Moreover, the presence of DNP at this low concentration contributed to an increase in hexose uptake such that it was substantially higher than that permitted by either of the two repressive sugars alone. When the cultures were maintained in medium containing D-fructose in place of glucose, a marked increase in uptake occurred, and this increase (derepression) was not affected by DNP. The derepression due to glucose deprivation and the increases caused by DNP treatment were also observed when 3-O-methylglucose was used to measure hexose transport. Although cultures maintained in the presence of glucosamine exhibited a repressed hexose transport rate, they did not generate significant amounts of lactic acid. DNP, and other uncouplers of oxidative phosphorylation, promoted a derepressed state of hexose transport but did not stimulate the generation of lactate from glucosamine. These data suggest that the metabolic repression phenomena of hexose transport do not depend on glycolysis but rather on the "energized" state of the cell. The energized state of the cell may also be required for the super-repression of hexose transport that is especially apparent when protein synthesis is blocked by cycloheximide.

Animals↗
PubMed1998

A non-invasive selective assessment of type I fibre mitochondrial function using 31P NMR spectroscopy. Evidence for impaired oxidative phosphorylation rate in skeletal muscle in patients with chronic heart failure.

BACKGROUND: Skeletal muscle abnormalities contribute considerably to the clinical expression of heart failure. Deconditioning, underperfusion and an increased number of type IIb glycolytical fibres lead to early lactate production and muscle fatigue at low exercise levels. Aerobic muscle metabolism may also be impaired, as suggested by biopsy studies. Thus far, no data are available from non-invasive studies to indicate the extent of aerobic muscle dysfunction during low-grade exercise which does not induce acidosis. METHODS AND RESULTS: Mitochondrial function of skeletal muscle during fibre type I activation was studied in 22 patients with chronic heart failure [NYHA class III, left ventricular ejection fraction 28 +/- 2%, (patients)] on ACE inhibitors, diuretics and digoxin, and in 20 normal subjects, using 31P NMR spectroscopy of a single right forearm flexor muscle during three mild intermittent exercise levels (0-40% of maximum voluntary contraction) and recovery time. At rest, the inorganic phosphate/phosphocreatine ratio was different [0.13 +/- 0.005 (patients) vs 0.09 +/- 0.002 (normal subjects), P = 0.0001]. However, intracellular pH was comparable. Local acidosis (tissue pH < 6.9) was avoided to prevent fibre type IIb activation. Calculated resting phosphate potential levels were comparable, but the slope and intercept of the linear relationship of phosphate potential and workload were significantly lower in patients than in normal subjects (11.7 +/- 0.7 vs 15.8 +/- 0.6 and 139 +/- 7 vs 196 +/- 7, patients vs normal subjects, indicating early exhaustion of intracellular energy at lower exercise levels. Also, maximum calculated workload at which tissue ADP stabilized was lower in patients than in normal subjects (88 +/- 7% vs 120 +/- 4% of maximum voluntary workload, patients vs normal subjects, P < 0.05). Time to recovery to pre-test phosphocreatine levels was prolonged by 46% in patients compared to normal subjects (P < 0.05). CONCLUSIONS: In heart failure, oxidative fibre mitochondrial function in skeletal muscle is impaired, as reflected by the reduced phosphate potential and oxidative phosphorylation rate, early exhaustion and slowed recovery of intracellular energy reserve at workloads, which do not affect intracellular pH.

Adenosine Triphosphate↗
PubMed1994

"Radical theory" of oxidative phosphorylation and photophosphorylation.

Ketyl radicals of acetone, dihydroxy acetone, and cardiolipin ketone react in 1,2-dimethoxyethane with inorganic phosphate (model: diethyl phosphate) to form phosphate esters of isopropanol, glycerol, or cardiolipin, respectively. After administration of diethyl phosphate to phosphate-impoverished rats, cardiolipin diethyl phosphate (probably as enol phosphate) has been isolated from liver mitochondria. Hence it is assumed that the enol phosphates of cardiolipin or of an analogous compound (mitochondria and chloroplasts) can be considered as high-energy intermediates of both oxidative and photochemical phosphorylation. Moreover, owing to earlier investigations which show that the formation of the phosphoric-acid-anhydride bond occurs proton-catalytically by acidolysis of enol phosphates, it is attempted here to combine the classic theories--"Chemical Coupling", "Chemiosmosis", and "Cooperativity", including the "Collision Hypothesis"--into the "Radical Theory of Oxidative Phosphorylation and Photophosphorylation".

Animals↗