1,720,958 research outputs found
Regulation of mitochondrial ATP synthesis by calcium: Evidence for a long-term metabolic priming
No full textIn recent years, mitochondria have emerged as important targets of agonist-dependent increases in cytosolic Ca(2+) concentration. Here, we analyzed the significance of Ca(2+) signals for the modulation of organelle function by directly measuring mitochondrial and cytosolic ATP levels ([ATP](m) and [ATP](c), respectively) with specifically targeted chimeras of the ATP-dependent photoprotein luciferase. In both HeLa cells and primary cultures of skeletal myotubes, stimulation with agonists evoking cytosolic and mitochondrial Ca(2+) signals caused increases in [ATP](m) and [ATP](c) that depended on two parameters: (i) the amplitude of the Ca(2+) rise in the mitochondrial matrix, and (ii) the availability of mitochondrial substrates. Moreover, the Ca(2+) elevation induced a long-lasting priming that persisted long after agonist washout and caused a major increase in [ATP](m) upon addition of oxidative substrates. These results demonstrate a direct role of mitochondrial Ca(2+) in driving ATP production and unravel a form of cellular memory that allows a prolonged metabolic activation in stimulated cells
Regulation of mitochondrial ATP syntesis by calcium: evidence for a long-term metabolic priming.
No full textIn recent years, mitochondria have emerged as important targets of agonist-dependent increases in cytosolic Ca(2+) concentration. Here, we analyzed the significance of Ca(2+) signals for the modulation of organelle function by directly measuring mitochondrial and cytosolic ATP levels ([ATP](m) and [ATP](c), respectively) with specifically targeted chimeras of the ATP-dependent photoprotein luciferase. In both HeLa cells and primary cultures of skeletal myotubes, stimulation with agonists evoking cytosolic and mitochondrial Ca(2+) signals caused increases in [ATP](m) and [ATP](c) that depended on two parameters: (i) the amplitude of the Ca(2+) rise in the mitochondrial matrix, and (ii) the availability of mitochondrial substrates. Moreover, the Ca(2+) elevation induced a long-lasting priming that persisted long after agonist washout and caused a major increase in [ATP](m) upon addition of oxidative substrates. These results demonstrate a direct role of mitochondrial Ca(2+) in driving ATP production and unravel a form of cellular memory that allows a prolonged metabolic activation in stimulated cells
Glucose generates sub-plasma membrane ATP microdomains in single islet beta-cells. Potential role for strategically located mitochondria.
No full textIncreases in the concentration of free ATP within the islet beta-cell may couple elevations in blood glucose to insulin release by closing ATP-sensitive K+ (KATP) channels and activating Ca2+ influx. Here, we use recombinant targeted luciferases and photon counting imaging to monitor changes in free [ATP] in subdomains of single living MIN6 and primary beta-cells. Resting [ATP] in the cytosol ([ATP]c), in the mitochondrial matrix ([ATP]m), and beneath the plasma membrane ([ATP]pm) were similar ( approximately 1 mM). Elevations in extracellular glucose concentration (3-30 mM) increased free [ATP] in each domain with distinct kinetics. Thus, sustained increases in [ATP]m and [ATP]pm were observed, but only a transient increase in [ATP]c. However, detectable increases in [ATP]c and [ATP]pm, but not [ATP]m, required extracellular Ca2+. Enhancement of glucose-induced Ca2+ influx with high [K+] had little effect on the apparent [ATP]c and [ATP]m increases but augmented the [ATP]pm increase. Underlying these changes, glucose increased the mitochondrial proton motive force, an effect mimicked by high [K+]. These data support a model in which glucose increases [ATP]m both through enhanced substrate supply and by progressive Ca2+-dependent activation of mitochondrial enzymes. This may then lead to a privileged elevation of [ATP]pm, which may be essential for the sustained closure of KATP channels. Luciferase imaging would appear to be a useful new tool for dynamic in vivo imaging of free ATP concentration
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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