Sepsis Induces Diaphragm Electron Transport Chain Dysfunction and Protein Depletion

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Abstract
Rationale: Sepsis significantly alters skeletal muscle mitochondrial function, but the mechanisms responsible for this abnormality are unknown. Objectives: We postulated that endotoxin elicits specific changes in electron transport chain proteins that produce derangements in mitochondrial function. To examine this issue, we compared the effects of endotoxin-induced sepsis on mitochondrial ATP (adenosine triphosphate) formation and electron transport chain protein composition. Methods and Measurements: Diaphragm mitochondrial oxygen consumption and mitochondrial nicotinamide adenine dinucleotide, reduced form, oxidase assays were measured in control rats (n = 13) and rats given endotoxin (8 mg/kg/d) for 12 (n = 14), 24 (n = 14), 36 (n = 14), and 48 h (n = 13). Electron transport chain subunits from Complexes I, III, IV, and V were isolated using Blue Native polyacrylamide gel electrophoresis techniques. Main Results: Endotoxin administration: 1) elicited large reductions in mitochondrial oxygen consumption (e.g., 201 ± 3.9 SE natoms O/min/mg for controls and 101 ± 4.5 SE natoms O/minutes/mg after 48 h endotoxin, p < 0.001), in nicotinamide adenine dinucleotide, reduced form, oxidase activity (p < 0.002), and in uncoupled respiration (p < 0.001) and 2) induced selective reductions in two subunits of Complex I, three subunits of Complex III, one subunit of Complex IV, and one subunit of Complex V. The time course of depletion of protein subunits mirrored alterations in oxygen consumption. Conclusions: Our data indicate that endotoxin selectively depletes critical components of the electron transport chain that diminishes electron flow, reduces proton pumping and decreases ATP formation.

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