Biomedical subjects

Ernst-Bernhard Kayser

Publications and source records attributed to Ernst-Bernhard Kayser.

5 recordsLinked to original sources

PubMed2006

Mitochondrial complex I function modulates volatile anesthetic sensitivity in C. elegans.

Despite the widespread clinical use of volatile anesthetics, their mechanisms of action remain unknown [1-6]. An unbiased genetic screen in the nematode C. elegans for animals with altered volatile anesthetic sensitivity identified a mutant in a nuclear-encoded subunit of mitochondrial complex I [7,8]. This raised the question of whether mitochondrial dysfunction might be the primary mechanism by which volatile anesthetics act, rather than an untoward secondary effect [9,10]. We report here analysis of additional C. elegans mutations in orthologs of human genes that contribute to the formation of complex I, complex II, complex III, and coenzyme Q [11-14]. To further characterize the specific contribution of complex I, we generated four hypomorphic C. elegans mutants encoding different complex I subunits [15]. Our main finding is the identification of a clear correlation between complex I-dependent oxidative phosphorylation capacity and volatile anesthetic sensitivity. These extended data link a physiologic determinant of anesthetic action in a tractable animal model to similar clinical observations in children with mitochondrial myopathies [16]. This work is the first to specifically implicate complex I-dependent oxidative phosphorylation function as a primary mediator of volatile anesthetic effect.

Anesthetics↗

PubMed2004

Mitochondrial oxidative phosphorylation is defective in the long-lived mutant clk-1.

The long-lived mutant of Caenorhabditis elegans, clk-1, is unable to synthesize ubiquinone, CoQ(9). Instead, the mutant accumulates demethoxyubiquinone(9) and small amounts of rhodoquinone(9) as well as dietary CoQ(8). We found a profound defect in oxidative phosphorylation, a test of integrated mitochondrial function, in clk-1 mitochondria fueled by NADH-linked electron donors, i.e. complex I-dependent substrates. Electron transfer from complex I to complex III, which requires quinones, is severely depressed, whereas the individual complexes are fully active. In contrast, oxidative phosphorylation initiated through complex II, which also requires quinones, is completely normal. Here we show that complexes I and II differ in their ability to use the quinone pool in clk-1. This is the first direct demonstration of a differential interaction of complex I and complex II with the endogenous quinone pool. This study uses the combined power of molecular genetics and biochemistry to highlight the role of quinones in mitochondrial function and aging.

Animals↗

PubMed2004

The effects of complex I function and oxidative damage on lifespan and anesthetic sensitivity in Caenorhabditis elegans.

A mutation in a subunit of complex I of the mitochondrial electron transport chain (gas-1) causes Caenorhabditis elegans to be hypersensitive to volatile anesthetics and oxygen as well as shortening lifespan. We hypothesized that changes in mitochondrial respiration or reactive oxygen species production cause these changes. Therefore, we compared gas-1 to other mitochondrial mutants to identify the relative importance of these two aspects of mitochondrial function in determining longevity. Lifespans of gas-1 and mev-1 were decreased compared with N2, while that of clk-1 was increased. Rates of oxidative phosphorylation were decreased in all three mutants, but the ROS damage was decreased only in clk-1. Suppressors of gas-1 increased rates of oxidative phosphorylation, decreased oxidative damage to mitochondrial proteins and increased lifespan. Two strains containing combinations of mutations predicted to have very decreased complex I function, had unexpectedly long lifespans. We conclude that mitochondrial changes in lifespan appear to be mediated primarily by changes in oxidative damage rather than by changes in rates of oxidative phosphorylation. In contrast, the effects of mitochondrial changes on anesthetic sensitivity appear to be mediated by both altered respiration and oxidative damage.

Anesthetics, Inhalation↗

PubMed2004

Mitochondrial complex I function affects halothane sensitivity in Caenorhabditis elegans.

BACKGROUND: : The gene gas-1 encodes a subunit of complex I of the mitochondrial electron transport chain in Caenorhabditis elegans. A mutation in gas-1 profoundly increases sensitivity of C. elegans to volatile anesthetics. It is unclear which aspects of mitochondrial function account for the hypersensitivity of the mutant. METHODS: : Oxidative phosphorylation was determined by measuring mitochondrial oxygen consumption using electron donors specific for either complex I or complex II. Adenosine triphosphate concentrations were determined by measuring luciferase activity. Oxidative damage to mitochondrial proteins was identified using specific antibodies. RESULTS: : Halothane inhibited oxidative phosphorylation in isolated wild-type mitochondria within a concentration range that immobilizes intact worms. At equal halothane concentrations, complex I activity but not complex II activity was lower in mitochondria from mutant (gas-1) animals than from wild-type (N2) animals. The halothane concentrations needed to immobilize 50% of N2 or gas-1 animals, respectively, did not reduce oxidative phosphorylation to identical rates in the two strains. In air, adenosine triphosphate concentrations were similar for N2 and gas-1 but were decreased in the presence of halothane only in gas-1 animals. Oxygen tension changed the sensitivity of both strains to halothane. When nematodes were raised in room air, oxidative damage to mitochondrial proteins was increased in the mutant animal compared with the wild type. CONCLUSIONS: : Rates of oxidative phosphorylation and changes in adenosine triphosphate concentrations by themselves do not control anesthetic-induced immobility of wild-type C. elegans. However, they may contribute to the increased sensitivity to volatile anesthetics of the gas-1 mutant. Oxidative damage to proteins may be an important contributor to sensitivity to volatile anesthetics in C. elegans.

Adenosine Diphosphate↗

PubMed2003

A mutation in mitochondrial complex I increases ethanol sensitivity in Caenorhabditis elegans.

BACKGROUND: The gene gas-1 encodes the 49-kDa subunit of complex I of the mitochondrial electron transport chain in Caenorhabditis elegans. A mutation in gas-1 profoundly increases sensitivity to ethanol and decreases complex I-dependent metabolism in mitochondria. METHODS: Mitochondria were isolated from wild-type and gas-1 strains of C. elegans. The effects of ethanol on complex I-, II-, and III-dependent oxidative phosphorylation were measured for mitochondria from each strain. Reversibility of the effects of ethanol was determined by measuring oxidative phosphorylation after removal of mitochondria from 1.5 M ethanol. The effects of ethanol on mitochondrial structure were visualized with electron microscopy. RESULTS: We found that ethanol inhibited complex I-, II-, and III-dependent oxidative phosphorylation in isolated wild-type mitochondria at concentrations that immobilize intact worms. It is important to note that the inhibitory effects of ethanol on mitochondria from either C. elegans or rat skeletal muscle were reversible even at molar concentrations. Complex I activity was lower in mitochondria from gas-1 animals than in mitochondria from wild-type animals at equal ethanol concentrations. Complex II activity was higher in gas-1 than in wild-type mitochondria at all concentrations of ethanol. No difference was seen between the strains in the sensitivity of complex III to ethanol. CONCLUSIONS: The difference in ethanol sensitivities between gas-1 and wild-type nematodes results solely from altered complex I function. At the respective concentrations of ethanol that immobilize whole animals, mitochondria from each strain of worms displayed identical rates of complex I-dependent state 3 respiration. We conclude that a threshold value of complex I activity controls the transition from mobility to immobility of C. elegans.

Animals↗