Influence of fixed electric charges on potential profile across the squid axon membrane

The potential profile for a model of squid axon membrane has been determined for two physiological states: resting and action states. The non-linear Poisson-Boltzmann equation has been solved by considering the volumetric charge densities due to charges dissolved in an electrolytic solution and fixed on both glycocalyx and cytoplasmatic proteins. Results showing the features of the potential profile along the outer electrolytic region are similar for both resting and action states. However, the potential fall along glycocalyx at action state is lower than at resting. A small variation in the Na+ concentration drastically affects the surface membrane potentials and vice versa. We conclude that effects on the potential profile due to surface lipidic bilayer charge and contiguous electric double layers are more relevant than those provoked by fixed charges distributed along the cell cytoplasm. (c) 2007 Elsevier B.V. All rights reserved.

Mitochondrial bioenergetics and redox state are unaltered in Trypanosoma cruzi isolates with compromised mitochondrial complex I subunit genes

In trypanosomatids the involvement of mitochondrial complex I in NADH oxidation has long been debated. Here, we took advantage of natural Trypanosoma cruzi mutants which present conspicuous deletions in ND4, ND5 and ND7 genes coding for complex I subunits to further investigate its functionality. Mitochondrial bioenergetics of wild type and complex I mutants showed no significant differences in oxygen consumption or respiratory control ratios in the presence of NADH-linked substrates or FADH(2)-generating succinate. No correlation could be established between mitochondrial membrane potentials and ND deletions. Since release of reactive oxygen species occurs at complex I, we measured mitochondrial H(2)O(2) formation induced by different substrates. Significant differences not associated to ND deletions were observed among the parasite isolates, demonstrating that these mutations are not important for the control of oxidant production. Our data support the notion that complex I has a limited function in T. cruzi.

Tissue-, substrate-, and site-specific characteristics of mitochondrial reactive oxygen species generation

Reactive oxygen species are a by-product of mitochondrial oxidative phosphorylation, derived from a small quantity of superoxide radicals generated during electron transport. We conducted a comprehensive and quantitative study of oxygen consumption, inner membrane potentials, and H(2)O(2) release in mitochondria isolated from rat brain, heart, kidney, liver, and skeletal muscle, using various respiratory substrates (alpha-ketoglutarate, glutamate, succinate, glycerol phosphate, and palmitoyl carnitine). The locations and properties of reactive oxygen species formation were determined using oxidative phosphorylation and the respiratory chain modulators oligomycin, rotenone, myxothiazol, and antimycin A and the Uncoupler CCCP. We found that in mitochondria isolated from most tissues incubated under physiologically relevant conditions, reactive oxygen release accounts for 0.1-0.2% of O(2) consumed. Our findings support an important participation of flavoenzymes and complex III and a substantial role for reverse electron transport to complex I as reactive oxygen species sources. Our results also indicate that succinate is an important substrate for isolated mitochondrial reactive oxygen production in brain, heart, kidney, and skeletal muscle, whereas fatty acids generate significant quantities of oxidants in kidney and liver. Finally, we found that increasing respiratory rates is an effective way to prevent mitochondrial oxidant release under many, but not all, conditions. Altogether, our data uncover and quantify many tissue-, substrate-, and site-specific characteristics of mitochondrial ROS release. (C) 2009 Elsevier Inc. All rights reserved.

trans, trans-2,4-decadienal induces mitochondrial dysfunction and oxidative stress

Lipid peroxidation produces a large number of reactive aldehydes as secondary products. We have previously shown that the reaction of cytochrome c with trans,trans-2, 4-decadienal (DDE), an aldehyde generated as a product of lipid peroxidation in cell membranes, results in the formation of adducts. Mass spectrometry analysis indicated that His-33, Lys-39, Lys-72 and Lys-100 in cytochrome c were modified by DDE. In the present work, we investigated the effect of DDE on isolated rat liver mitochondria. DDE (162 mu M) treatment increases the rate of mitochondrial oxygen consumption. Extensive mitochondrial swelling upon treatment with DDE (900 nM-162 mu M) was observed by light scattering and transmission electron microscopy experiments. DDE-induced loss of inner mitochondrial membrane potentials, monitored by safranin O fluorescence, was also observed. Furthermore, DDE-treated mitochondria showed an increase in lipid peroxidation, as monitored by MDA formation. These results suggest that reactive aldehydes promote mitochondrial dysfunction.

Effects of a high fat diet on liver mitochondria: increased ATP-sensitive K(+) channel activity and reactive oxygen species generation

High fat diets are extensively associated with health complications within the spectrum of the metabolic syndrome. Some of the most prevalent of these pathologies, often observed early in the development of high-fat dietary complications, are non-alcoholic fatty liver diseases. Mitochondrial bioenergetics and redox state changes are also widely associated with alterations within the metabolic syndrome. We investigated the mitochondrial effects of a high fat diet leading to non-alcoholic fatty liver disease in mice. We found that the diet does not substantially alter respiratory rates, ADP/O ratios or membrane potentials of isolated liver mitochondria. However, H(2)O(2) release using different substrates and ATP-sensitive K(+) transport activities are increased in mitochondria from animals on high fat diets. The increase in H(2)O(2) release rates was observed with different respiratory substrates and was not altered by modulators of mitochondrial ATP-sensitive K(+) channels, indicating it was not related to an observed increase in K(+) transport. Altogether, we demonstrate that mitochondria from animals with diet-induced steatosis do not present significant bioenergetic changes, but display altered ion transport and increased oxidant generation. This is the first evidence, to our knowledge, that ATP-sensitive K(+) transport in mitochondria can be modulated by diet.