Increase In Oxygen Flux Research Articles

Substrate use and temperature effects in flight muscle mitochondria from an endothermic insect, the hawkmoth Manduca sexta

Manduca sexta are endothermic insects, requiring adult thorax temperatures to be elevated above 35 °C for flight muscles to produce the wing beat frequencies necessary for flight. During flight, these animals rely on aerobic production of ATP by flight muscle mitochondria with several potential metabolic pathways providing the fuel. Along with typical carbohydrate substrates, mitochondria of other endothermic insects including bumblebees and wasps can use the amino acid proline or glycerol 3-phosphate (G3P) as metabolic fuel for prewarm up and flight. Here we examine flight muscle mitochondria physiology and the role of temperature and substrates in oxidative phosphorylation from 3-day old adult Manduca sexta. Mitochondria oxygen flux from flight muscle fibers were temperature sensitive with Q10 values ranging from 1.99 to 2.90, with a large increase in LEAK respiration with increased temperature. Mitochondria oxygen flux was stimulated by carbohydrate-based substrates, with flux through Complex I substrates providing the greatest oxygen flux. Neither proline nor G3P produced an increase in oxygen flux of the flight muscle mitochondria. Unlike other endothermic insects, Manduca are unable to supplement carbohydrate oxidation with either proline or G3P entering through Coenzyme Q and rely on substrates entering at complex I and II.

The role of ionic-electronic ratio in dual-phase catalytic layers for oxygen transport permeation membranes

Oxygen transport membrane (OTM) is an appealing technology for contributing to the decarbonization of the industry via oxy-combustion processes. Dual-phase composite materials are promising membrane candidates for this kind of processes due to their stability under CO2 atmospheres. Even so, the oxygen permeation through this kind of membranes is still limiting for practical application. A key well-studied membrane performance parameter is the ratio between composite crystalline phases since the percolative channels for each phase determine the final oxygen permeation flux. Here, we investigate the influence of the phase ratio on the surface-exchange reactions in catalytically-activated composite membranes composed of NiFe2O4 (NFO) and Ce0.8Tb0.2O2-δ (CTO). Electrical impedance spectroscopy (EIS) and oxygen permeation studies revealed a decrease in polarization resistance and an increase in oxygen flux as the ionic-phase proportion in the catalytic layers increases. At 850 °C, the 20NFO80CTO catalytic layer on a 650 μm-thick 50NFO50CTO membrane reaches an oxygen flux of 0.2 mL min−1·cm−2. That permeation was improved by a factor of 2.5 regarding the opposite phase ratio (80NFO20CTO) and 1.3 regarding a balanced phase ratio (50NFO50CTO) in the catalytic layer. The 20NFO80CTO electrodes showed the lowest resistances compared to the electrodes with higher NFO content, confirming that the O2 surface exchange is controlled by ionic-phase mechanisms rather than electronic phase ones.

Band offsets of ITO/amorphous GaO x heterojunction determined by x-ray photoemission spectra

The band offsets of heterojunctions formed between indium tin oxide (ITO) and amorphous gallium oxide (a-GaO x ) of different stoichiometric ratios were measured by x-ray photoelectron spectroscopy using the Kraut method. a-GaO x films with different stoichiometric ratios were deposited on commercial ITO/quartz substrates using radio frequency magnetron sputtering by varying the Ar/O2 flux ratio. With the increase of oxygen flux in the reaction gas, the oxygen vacancy (VO) concentration of a-GaO x decreases and its bandgap increases from 5.2 eV to 5.32 eV, while the valence band offset of ITO/a-GaO x heterojunction changes from 0.29 ± 0.07 eV to −0.74 ± 0.06 eV and conduction band offset changes from 0.95 ± 0.085 to 2.10 ± 0.075 eV. The results indicate that the band alignment of ITO/a-GaO x heterojunction can change from type I to type II with the variation of Ga/O stoichiometric ratio, which can provide guidance for the design of their corresponding high-performance heterostructured devices.

Modulation of oxidative neurometabolism in ischemia/reperfusion by nitrite.

Nitrite has been viewed essentially as an inert metabolic endpoint of nitric oxide (•NO). However, under certain conditions, nitrite can be a source of •NO. In the brain, this alternative source of •NO production independent of nitric oxide synthase activity may be particularly relevant in ischemia/reperfusion (I/R), where low oxygen availability limits enzymatic production of •NO. Notably, in vivo concentration of nitrite can be easily increased with diet, through the ingestion of nitrate-rich foods, opening the window for a therapeutic intervention based on diet. Considering the modulation of mitochondrial respiration by •NO, we have hypothesized that the protective action of nitrite in I/R may also result from modulation of mitochondrial function. We used high-resolution respirometry to evaluate the effects of nitrite in two in vitro models of I/R. In both cases, an increase in oxygen flux was observed following reoxygenation, a phenomenon that has been coined "oxidative burst". The amplitude of this "oxidative burst" was decreased by nitrite in a concentration-dependent manner. Additionally, a pilot in vivo study in which animals received a nitrate-rich diet as a strategy to increase circulating and tissue levels of nitrite also revealed that the "oxidative burst" was decreased in the nitrate-treated animals. These results may provide mechanistic support to the observation of a protective effect of nitrite in situations of brain ischemia.

Optimization of active antireflection ZnO films for p-GaAs-based heterojunction solar cells

We have optimized the photovoltaic properties of active ZnO/p-GaAs heterojunction solar cells by pulsed laser deposition method by varying the oxygen pressure from 0 to 50 mTorr during the fabrication process. We observed the crystallinity and grain size of ZnO enhanced with increasing oxygen pressure from 0 to 30 mTorr. In addition, with this increase of oxygen flux, the intensity of E1(LO) modes obtained by Raman measurements declines significantly and almost disappears under an oxygen pressure of 50 mTorr. The change of intensity is assumed to be the change of oxygen vacancy and zinc interstitial concentrations in ZnO films with oxygen pressures. Current-voltage measurements and extractions show that ZnO grown at 30 mTorr displays the best performance with the ISC of 24.3 mA/cm2, the efficiency of 8.746 %, and FF0 of 68.73 %. The high performance of the heterojunction solar cell grown at the oxygen partial pressure of 30 mTorr might be due to the reduction of oxygen vacancies by increasing oxygen during the deposition. The results reveal the importance of the oxygen processing gas in promoting devices performance.

Guanosine protects against behavioural and mitochondrial bioenergetic alterations after mild traumatic brain injury

Traumatic brain injury (TBI) constitutes a heterogeneous cerebral insult induced by traumatic biomechanical forces. Mitochondria play a critical role in brain bioenergetics, and TBI induces several consequences related with oxidative stress and excitotoxicity clearly demonstrated in different experimental model involving TBI. Mitochondrial bioenergetics alterations can present several targets for therapeutics which could help reduce secondary brain lesions such as neuropsychiatric problems, including memory loss and motor impairment. Guanosine (GUO), an endogenous neuroprotective nucleoside, affords the long-term benefits of controlling brain neurodegeneration, mainly due to its capacity to activate the antioxidant defense system and maintenance of the redox system. However, little is known about the exact protective mechanism exerted by GUO on mitochondrial bioenergetics disruption induced by TBI. Thus, the aim of this study was to investigate the effects of GUO in brain cortical and hippocampal mitochondrial bioenergetics in the mild TBI model. Additionally, we aimed to assess whether mitochondrial damage induced by TBI may be related to behavioral alterations in rats. Our findings showed that 24 h post-TBI, GUO treatment promotes an adaptive response of mitochondrial respiratory chain increasing oxygen flux which it was able to protect against the uncoupling of oxidative phosphorylation (OXPHOS) induced by TBI, restored the respiratory electron transfer system (ETS) established with an uncoupler. Guanosine treatment also increased respiratory control ratio (RCR), an indicator of the state of mitochondrial coupling, which is related to the mitochondrial functionality. In addition, mitochondrial bioenergetics failure was closely related with locomotor, exploratory and memory impairments. The present study suggests GUO treatment post mild TBI could increase GDP endogenous levels and consequently increasing ATP levels promotes an increase of RCR increasing OXPHOS and in substantial improve mitochondrial respiration in different brain regions, which, in turn, could promote an improvement in behavioral parameters associated to the mild TBI. These findings may contribute to the development of future therapies with a target on failure energetic metabolism induced by TBI.

Yerba mate increases mitochondrial uncoupling in adipose tissue

Yerba mate is commonly consumed in cultures throughout Central and South America with decades of research revealing numerous effects, including improvements in cardiometabolic outcomes. Among these benefits is an increased resistance to weight gain, as well as altered energy expenditure. However, additional research is needed to elucidate the effects of yerba mate on mitochondrial parameters. Through cell culture and rodent models, we tested mitochondrial respiration and ATP production in adipose to determine the direct effects of yerba mate on mitochondrial coupling status. We found that adipocytes experienced a substantial increase in oxygen flux, without a comparable increase in ATP generation, indicating increased mitochondrial uncoupling. Similar findings were observed in subcutaneous adipose tissue in rodents fed yerba mate chronically. These observations in subcutaneous adipose, which is unique in its capacity to “beige” or undergo mitochondrial biogenesis and uncoupling. Altogether, these results suggest that a portion of the metabolic benefit of regular consumption of yerba mate may be a result of increased adipose mitochondrial uncoupling.Support or Funding InformationNone.

Formation mechanisms of etched feature profiles during Si etching in Cl2/O2 plasmas

Feature profiles of poly-Si etched in Cl2/O2 plasmas have been analyzed through a mechanistic comparison between experiments and simulations. The emphasis was placed on a comprehensive understanding of the formation mechanisms for profile anomalies of tapering, microtrenching, and footing (or corner rounding near the feature bottom). Experiments were conducted in a commercial etching reactor with ultra-high-frequency plasmas by varying O2 percentage, wafer stage temperature, rf bias power, and feed gas pressure. Simulations of the feature profile evolution were done by using a semiempirical, atomic-scale cellular model based on the Monte Carlo method that we have developed. The experiments indicated that sidewall profiles become more tapered with increasing O2 addition to Cl2 plasmas, while microtrenching and footing are pronounced in pure Cl2 plasma, being suppressed with increasing O2. A comparison with the simulations indicated that the tapered profiles are caused by the deposition of etch products/by-products on feature sidewalls from the plasma, being enhanced with increasing oxygen flux (due to synergistic effects between deposition of products/by-products and surface oxidation) and being reduced with increasing ion energy and neutral reactant flux. On the other hand, the footing is attributed to the redeposition of etch products on sidewalls from the feature bottom being etched, being reduced with increasing oxygen flux, ion energy, and neutral reactant flux. Microtrenching is caused by the ion reflection from feature sidewalls on incidence, being reduced with increasing oxygen flux (partly due to surface oxidation of the feature bottom) and being enhanced and then reduced with increasing ion energy and neutral reactant flux. The tapering, footing, and microtrenching were found to be closely related to each other: the footing near the feature bottom fades away under conditions of increased tapering of sidewalls, and the microtrenching is affected significantly by the degree of footing as well as the taper angle of the sidewalls.

6-Hydroxydopamine induces different mitochondrial bioenergetics response in brain regions of rat

Mitochondrial dysfunction has been demonstrated to have a central role in Parkinson Disease (PD) pathophysiology. Some studies have indicated that PD causes an impairment in mitochondrial bioenergetics; however, the effects of PD on brain-region specific bioenergetics was never investigated before. This study aimed to evaluate mitochondrial bioenergetics in different rat brain structures in an in vitro model of PD using 6-OHDA. Rat brain slices of hippocampus, striatum, and cortex were exposed to 6-OHDA (100 μM) for 1 h and mitochondrial bioenergetic parameters, peroxide production, lactate dehydrogenase (LDH) and citrate synthase (CS) activities were analyzed. Hippocampus slices exposed to 6-OHDA presented increased peroxide production but, no mitochondrial adaptive response against 6-OHDA damage. Cortex slices exposed to 6-OHDA presented increased oxygen flux related to oxidative phosphorylation and energetic pathways exchange demonstrated by the increase in LDH activity, suggesting a mitochondrial compensatory response. Striatum slices exposed to 6-OHDA presented a decrease of oxidative phosphorylation and decrease of oxygen flux related to ATP-synthase indicating an impairment in the respiratory chain. The co-incubation of 6-OHDA with n-acetylcysteine (NAC) abolished the effects of 6-OHDA on mitochondrial function in all brain regions tested, indicating that the increased reactive oxygen species (ROS) production is responsible for the alterations observed in mitochondrial bioenergetics. The present results indicate a brain-region specific response against 6-OHDA, providing new insights into brain mitochondrial bioenergetic function in PD. These findings may contribute to the development of future therapies with a target on energy metabolism.

Experimental investigation of the impact of oxygen flux on the burning dynamics of forest fuel beds

To characterize the burning dynamics of porous wildland fuels it is fundamental to understand the heat and mass transfer mechanisms. These are significantly different compared to solid fuels and less well documented. Radiation feedback from flames and convective heat transfer from forced airflow have been found to influence the pyrolysis and combustion processes. Smoldering combustion and resulting heat feedback is also shown to have significant impact. The link between burning dynamics and the oxygen availability is also explored. Combustion experiments are carried out using the FM Global Fire Propagation Apparatus in order to investigate changes in the burning behavior of porous fuel beds as a function of the oxygen availability. The oxygen flux into the combustion zone was varied by three mechanisms, (1) varying natural entrainment, (2) changing forced flow magnitude and (3) oxygen concentration. Results investigated from the combustion tests were the duration of flaming (from which the average burning rate was deduced), CO and CO2 generation rates, combustion efficiency and heat release rate. For both test series, the duration of flaming decreased and peak heat release rate increased with increasing oxygen flux. For tests with varying flow magnitude the combustion efficiency stayed constant with a CO/CO2 ratio below 1.5%. For tests with varying flow oxygen concentration the ratio was much higher, between 12% and 26%, indicating high levels of incomplete combustion. At a given oxygen flux, changes in heat flux feedback from the flames, convection cooling, and combustion efficiency were found to be the reason for differences on the order of 30–50% in burning rate and thus heat release rate. The intensity of smoldering increased with increasing oxygen flux equally for both tests series. The study explored herein provides insight into importance of several heat and mass transfer mechanisms that govern the burning dynamics of porous wildland fuel beds. Furthermore, it also highlights the necessity of understanding incomplete combustion (flaming) in the wildfire context.

Annealing-free copper source-drain electrodes based on copper–calcium diffusion barrier for amorphous silicon thin film transistor

The copper (Cu) source-drain electrodes based on copper–calcium (CuCa) diffusion barrier were fabricated without annealing process and in one wet etching step in order to develop the applications of Cu in hydrogenated amorphous silicon thin film transistor (α-Si:H TFT). The results show that oxygen flux and substrate temperature in depositing CuCa buffer layer affect greatly the adhesion of source-drain electrodes, and a perfect adhesion was obtained by an increasing oxygen flux to 4sccm or an increasing substrate temperature to 150°C, despite no annealing process. The specific resistance of source-drain electrodes has a slight increase with the increasing oxygen flux or substrate temperature or CuCa thickness. Auger electron spectroscopy (AES) show that the CuCa alloy barrier layer has perfect anti-diffusion between Cu film and α-Si:H. A much-desired taper angle of 43.4° and a little critical dimension (CD) bias of 0.91μm for the Cu/CuCa electrodes were obtained in one wet etching step. The α-Si:H TFT with the Cu/CuCa source-drain electrodes demonstrated the field-effect mobility of 0.73cm2/Vs, the subthreshold slope of 0.73V/dec, the threshold voltage of 0.45V, and the Ion/Ioff ratio of 106 due to the superior performances of the source-drain electrodes with the desired adhesion, specific resistance and taper angle despite no annealing process.

Blood Flow and Oxygen Transport in Descending Branch of Lateral Femoral Circumflex Arteries After Transfemoral Amputation: A Numerical Study

This study investigates atherosclerotic development in the descending branch of the lateral femoral circumflex artery (DLFCA) after transfemoral amputation and assesses the effects of blood velocity during exercise on the oxygen transport of the residuum DLFCA. Computational fluid dynamics models of DLFCAs coupled with oxygen transport in both the residuum and the sound contralateral limb were established. The profiles for three blood velocity profiles were applied at the inlet of the residuum DLFCA model. The results show that in comparison with the sound limb, blood velocity in the residuum DLFCA was higher, the number of low-wall-shear-stress (WSS) regions was smaller, the Sherwood number for the arterial wall was smaller, and there were more hypoxia zones. An increase in blood velocity in the residuum DLFCA resulted in increases in WSS and the Sherwood number and reductions in the numbers of low-WSS regions and hypoxia zones. The rate of atherosclerosis in the residuum is lower than that of the sound limb in terms of WSS, whereas the rate of atherosclerosis in the sound limb is lower than that of the residuum in terms of hypoxia. Overall, both WSS and oxygen transport need to be considered in order to precisely predict atherosclerosis development in the lower-limb arteries after amputation. In addition, exercise is beneficial for oxygen transport, with an increase in oxygen flux to the arterial wall, and is helpful for the prevention and control of atherosclerosis in the arteries of the residuum.

Overlapping Role of Respiratory Supercomplex Factor Rcf2 and Its N-terminal Homolog Rcf3 in Saccharomyces cerevisiae

The mitochondrial electron transport chain consists of individual protein complexes arranged into large macromolecular structures, termed respiratory chain supercomplexes or respirasomes. In the yeast Saccharomyces cerevisiae, respiratory chain supercomplexes form by association of the bc1 complex with the cytochrome c oxidase. Formation and maintenance of these assemblies are promoted by specific respiratory supercomplex factors, the Rcf proteins. For these proteins a regulatory function in bridging the electron transfer within supercomplexes has been proposed. Here we report on the maturation of Rcf2 into an N- and C-terminal peptide. We show that the previously uncharacterized Rcf3 (YBR255c-A) is a homolog of the N-terminal Rcf2 peptide, whereas Rcf1 is homologous to the C-terminal portion. Both Rcf3 and the C-terminal fragment of Rcf2 associate with monomeric cytochrome c oxidase and respiratory chain supercomplexes. A lack of Rcf2 and Rcf3 increases oxygen flux through the respiratory chain by up-regulation of the cytochrome c oxidase activity. A double gene deletion of RCF2 and RCF3 affects cellular survival under non-fermentable growth conditions, suggesting an overlapping role for both proteins in the regulation of the OXPHOS activity. Furthermore, our data suggest an association of all three Rcf proteins with the bc1 complex in the absence of a functional cytochrome c oxidase and identify a supercomplex independent interaction network of the Rcf proteins.

(Invited) MIEC Materials for Membrane Applications: Enhancing the Oxygen Transport

Mixed ionic-electronic conducting (MIEC) materials are of great interest for a variety of high-temperature applications, such as dense ceramic oxygen transport membranes (OTMs) for gas separation. Several MIEC perovskite oxides, e.g., Ba0.5Sr0.5Co0.8Fe0.2O3-δ, La0.58Sr0.4Co0.2Fe0.8O3-δ, or La0.6Sr0.4CoO3-δ exhibit excellent oxygen-ionic and electronic transport properties and are, hence, promising candidates for high-permeation OTMs. It is essential, though, to determine their chemical stability and electrochemical transport properties (D δ and k δ) over a broad range of oxygen partial pressure pO2 first. This can both be achieved in a custom-made zirconia “oxygen pump” setup. Surface oxygen exchange (k δ) becomes rate-determining for oxygen permeation of high-performing thin OTMs. Further increase of oxygen flux requires an enhancement of surface exchange. This can be achieved by modifying the OTM surfaces with a porous functional layer. With the help of a 3D FEM OTM model the interplay of transport parameters and functional-layer microstructure (thickness, porosity, particle sizes) can be readily assessed.

Improvement of oxygen permeation through microchanneled ceramic membranes

Microchanneled membranes have demonstrated high oxygen permeation fluxes owing to the shortened oxygen permeation distance and the enlarged membrane surface area. In this study, further improvement of the oxygen permeation flux has been attempted through using dual-phase membranes and applying catalysts on the membrane surfaces. Compared with pure La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) membranes, LSCF–Ce0.8Gd0.2O2−δ (GDC) dual-phase membranes increased oxygen flux by 57% due to the balanced oxygen ionic and electronic conductivities. The open microchannel structure facilitated the coating of catalysts on both sides of the membranes because catalyst can readily be delivered to the membrane surface on the microchannel side through the numerous microchannels. The catalyst increased the oxygen fluxes of both pure LSCF membranes and dual-phase membranes, while it had a larger effect on the dual-phase membranes because its surface reactions play a more significant role in controlling the overall oxygen permeation. Finally, the improvements increased oxygen flux through the microchanneled membranes from 1.4 to 3.8mlcm−2min−1 at 950°C, i.e. by a factor of 2.7.

Influence of sputtering parameters on the electrical property of indium tin oxide film used for microwave absorbing

The indium tin oxide films used for microwave absorbing were prepared on unheated glass substrate by DC magnetron sputtering system. In order to control the square resistance of ITO films effectively, the influence of sputtering power, time and oxygen flux on the property of ITO films was investigated. The results showed that changing the sputtering power and time can regulate the square resistance of films on a small scale and the square resistance will increase continuously to a large value with the increasing oxygen flux. The sputtering parameters provide ITO thin films with good transmittance (70–90% in 350–800nm spectra) and wide-ranged square resistance (from 20Ω/□ to 4800Ω/□).

Modeling Low-Platinum-Loading Effects in Fuel-Cell Catalyst Layers

The cathode catalyst layer within a proton-exchange-membrane fuel cell is the most complex and critical, yet least understood, layer within the cell. The exact method and equations for modeling this layer are still being revised and will be discussed in this paper, including a 0.8 reaction order, existence of Pt oxide, possible non-isopotential agglomerates, and the impact of a film resistance towards oxygen transport. While the former assumptions are relatively straightforward to understand and implement, the latter film resistance is shown to cause increased mass-transport limitations with low Pt-loading catalyst layers. Model results demonstrate that the increased oxygen flux and/or diffusion pathway through the film can substantially decrease performance. Also, some scale-up concepts from the agglomerate scale to the more macroscopic porous-electrode scale are discussed and the resulting optimization scenarios investigated.

Bi-doping effects on the structure and oxygen permeation properties of BaSc 0.1Co 0.9O 3− δ perovskite membranes

In this work, we investigate the effect of partial substitution of bismuth oxide on BaSc 0.1Co 0.9O 3− δ perovskite membranes. Doping was carried out in the A-site (Ba 1− x Bi x Sc 0.1Co 0.9O 3− δ ) and B-site (BaBi x Sc 0.1Co 0.9− x O 3− δ ). Bi doping at or below 10% ( x ≤ 0.10) in both sites resulted in significant increase of oxygen flux, up to two orders of magnitude at the low to medium temperature range (650–850 °C) as compared to non-doped disk membranes. Among all compositions, B-site doped x = 0.05 showed the highest oxygen fluxes, reaching 2.17 ml min −1 cm −2 at 950 °C. These results suggest that Bi doping at or below 10% conferred superior ionic oxygen diffusion transport, owing to the formation of cubic structures. Further increases in the Bi-doping amount formed non-cubic structure delivering very low oxygen fluxes. The structure transition phenomena from non-cubic to cubic crystal lattices occurred for non-doped and A-site doped membrane with 20 and 30% mole bismuth oxide in excess of 800 °C, concomitantly with increases in oxygen fluxes and sharp rise of electrical conductivity. A-site and B-site doped x = 0.05 compounds exposed to nitrogen atmosphere at 850 °C for 7 days showed reasonable stable structure.

Microstructure of epitaxial rutile TiO 2 films grown by molecular beam epitaxy on r-plane Al 2O 3

The paper reports on the microstructure of rutile TiO 2 films grown on r-plane sapphire surfaces by molecular beam epitaxy as a function of oxygen flux during growth. Single-phase, epitaxial rutile films were obtained for all growth conditions. X-ray diffraction and transmission electron microscopy showed that the films contained a high density of twins, likely as a result of different variants nucleating on the substrate simultaneously. At low oxygen fluxes, surface features were dominated by twin variants. With increasing oxygen flux, the surface morphology changed due to the reduced mobility of ad-atoms. The relationship between the arrangements of oxygen octahedra in the sapphire and rutile structures, the epitaxial orientation and twin formation is discussed.

Melatonin protects the mitochondria from oxidative damage reducing oxygen consumption, membrane potential, and superoxide anion production

The role of melatonin in improving mitochondrial respiratory chain activity and increasing ATP production in different experimental conditions has been widely reported. To date, however, the mechanism(s) involved are largely unknown. Using high-resolution respirometry, fluorometry and spectrophotometry we studied the effects of melatonin on normal mitochondrial functions. Mitochondria were recovered from mouse liver cells and incubated in vitro with melatonin at concentrations ranging from 1 nm to 1 mm. Melatonin decreased oxygen consumption concomitantly with its concentration, inhibited any increase in oxygen flux in the presence of an excess of ADP, reduced the membrane potential, and consequently inhibited the production of superoxide anion and hydrogen peroxide. At the same time it maintained the efficiency of oxidative phosphorylation and ATP synthesis while increasing the activity of the respiratory complexes (mainly complexes I, III, and IV). The effects of melatonin appeared to be due to its presence within the mitochondria, since kinetic experiments clearly showed its incorporation into these organelles. Our results support the hypothesis that melatonin, together with hormones such as triiodothyronine, participates in the physiological regulation of mitochondrial homeostasis.