[Irreversible changes in energy processes in the mitochondria after chronic exposure to detergents].
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Chronic inhalational exposure of white rats to a synthetic detergent 'LOTOS' in concentrations 25 and 100 mg/m3 caused liver mitochondria bioenergetics changes from a reversible low energetic shift up to an irreversible mitochondria damage of an organ-structural character. The degree of the damaging effect depended on the duration of exposure and the concentration of the detergent.Keywords:
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The bioenergetic status of cells is tightly regulated by the activity of cytosolic enzymes and mitochondrial ATP production. To adapt their metabolism to cellular energy needs, mitochondria have been shown to exhibit changes in their ionic composition as the result of changes in cytosolic ion concentrations. Individual mitochondria also exhibit spontaneous changes in their electrical potential without altering those of neighboring mitochondria. We recently reported that individual mitochondria of intact astrocytes exhibit spontaneous transient increases in their Na+ concentration. Here, we investigated whether the concentration of other ionic species were involved during mitochondrial transients. By combining fluorescence imaging methods, we performed a multiparameter study of spontaneous mitochondrial transients in intact resting astrocytes. We show that mitochondria exhibit coincident changes in their Na+ concentration, electrical potential, matrix pH and mitochondrial reactive oxygen species production during a mitochondrial transient without involving detectable changes in their Ca2+ concentration. Using widefield and total internal reflection fluorescence imaging, we found evidence for localized transient decreases in the free Mg2+ concentration accompanying mitochondrial Na+ spikes that could indicate an associated local and transient enrichment in the ATP concentration. Therefore, we propose a sequential model for mitochondrial transients involving a localized ATP microdomain that triggers a Na+-mediated mitochondrial depolarization, transiently enhancing the activity of the mitochondrial respiratory chain. Our work provides a model describing ionic changes that could support a bidirectional cytosol-to-mitochondria ionic communication.
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Abstract Mitochondria are the main suppliers of neuronal adenosine triphosphate and play a critical role in brain energy metabolism. Mitochondria also serve as Ca 2+ sinks and anabolic factories and are therefore essential for neuronal function and survival. Dysregulation of neuronal bioenergetics is increasingly implicated in neurodegenerative disorders, particularly Parkinson's disease. This review describes the role of mitochondria in energy metabolism under resting conditions and during synaptic transmission, and presents evidence for the contribution of neuronal mitochondrial dysfunction to Parkinson's disease.
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The data obtained by the author during more than 30 years of studies of yeast energy metabolism at cellular and mitochondrial levels are summarized. The data suggest that tightly coupled yeast mitochondria represent not only a fully functional, but often a preferable model system for studying many problems of bioenergetics.
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[Irreversible changes in energy processes in the mitochondria after chronic exposure to detergents].
Chronic inhalational exposure of white rats to a synthetic detergent 'LOTOS' in concentrations 25 and 100 mg/m3 caused liver mitochondria bioenergetics changes from a reversible low energetic shift up to an irreversible mitochondria damage of an organ-structural character. The degree of the damaging effect depended on the duration of exposure and the concentration of the detergent.
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Bioenergetics
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Mitochondrial bioenergetics converges at the mitochondrial inner membrane and encompasses the proton gradient, mitochondrial membrane potential and respiration. Measuring these parameters can assess the mitochondrial functional state and consequently, the effectiveness of pharmacological manipulation of diseases involving mitochondrial dysfunctions. However, available technologies to assay mitochondrial functions are primarily limited to ensemble measurements, which mask the functional dynamics and variability of single mitochondria. These dynamics could provide a better understanding of mitochondrial bioenergetics and diseases related to mitochondrial dysfunctions. This thesis describes three developments to improve mitochondrial functional assays, with an ultimate goal of achieving single mitochondrial resolution.The first development is single mitochondrial respirometers that require only 1.5 pL of assay buffer and can measure respiration from one mitochondrion. The micro-respirometers consist of micron sized chambers etched out of glass substrates and coated with an oxygen sensitive phosphorescent dye Pt(II) meso-tetra(pentafluoropheny)porphine (PtTFPP). Sealing the chamberswith a polydimethylsiloxane layer coated with oxygen impermeable Viton rubber enables detection of single mitochondrial respiration.The second development is the fabrication of nanochannels capable of trapping single mitochondria for fluorescence analysis of their membrane potential. The use of these channels significantly reduces background noise and allows the ease of experimental buffer exchange. Experimental results show fluctuations of membrane potential at the single mitochondrial level.Finally, an integrated platform to detect extra-mitochondrial pH of isolated mitochondria is described. This platform was based on tethering mitochondria to one-atom thin graphene. The mitochondria are tethered via graphene bound antibodies, which recognize the mitochondrial outer membrane protein TOM20. Graphene is an excellent conductor and changes in the pH surrounding the mitochondria can change the graphene conductance and can be detected electrically. Being transparent, the graphene layer also permits optical interrogation of the mitochondria concurrent with the analysis of pH. Hence, this system permits the simultaneous monitoring of changes in extra-mitochondrial pH through graphene conductance and inner membrane potential using fluorescence. In addition, the integrated graphene system offers a unique scalability down to one mitochondrion without loss of electrical sensitivity.
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