1,721,013 research outputs found
The role of Gi-proteins and β-adrenoceptors in the age-related decline of contraction in guinea-pig ventricular myocytes
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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
Endothelin-1 and isoprenaline co-stimulation causes contractile failure which is partially reversed by MEK inhibition
No full textObjective: The mitogen-activated kinase kinases (MEK)-extracellular signal-regulated kinases (ERK) signaling pathway is activated by agonists like catecholamines or endothelin-1 (ET-1) and has been implicated in cardiac pathology, such as the progression from cardiac hypertrophy to failure. The purpose of the present study, performed in an in vitro model of contractile failure, was to evaluate whether MEK inhibition prevents functional deterioration. Methods and results: Contractile dysfunction was induced in reconstituted rat heart tissue by concomitant treatment with ET-1 (10 nmol/l) and isoprenaline (ISO, 10 nmol/l) for 5 days. While basal force of contraction was unchanged, contractile responsiveness to beta-adrenoceptor agonists was markedly impaired (active force declined to 51% of controls) and was associated with decreased lusitropy. Moreover, in ET-1 + ISO-treated heart tissues, reprogramming of gene expression was observed with an increased ratio of beta-myosin heavy chain (MHC) to alpha-MHC mRNA and increased transcript levels of ANF and skeletal/smooth Muscle alpha-actin isoforms. The MEK inhibitor U0126 (10 mu mol/l) almost completely prevented the reduction in p-adrenergic responsiveness and the negative lusitropic effect of ET-1+ISO co-stimulation. In addition, U0126 completely normalized ANF gene expression, but did not affect or only marginally affected expression of MHC and a-actin isoforms. Conclusions: These results suggest that interruption of the MEK-ERK signaling pathway with a specific MEK inhibitor prevents, in part, the occurrence of a pathologic phenotype secondary to excessive stimulation with neurotulmoral factors. The MEK-ERK pathway seems to be all important but not exclusive regulatory pathway responsible for the development of contractile dysfunction. (c) 2005 European Society of Cardiology. Published by Elsevier B.V All rights reserved
Alterations of the preproenkephalin system in cardiac hypertrophy and its role in atrioventricular conduction
No full textObjective: The goal of this study was to investigate alterations of the endogenous opioid system in cardiac hypertrophy, to elucidate mechanisms of preproenkephalin (ppENK) gene expression, and to assess effects of endogenous opioids on myocardial contractility and atrioventricular conduction. Methods: Hypertrophy was induced by ligation of a renal artery (2K1C) or chronic isoprenaline infusion (ISO). ppENK and opioid receptor (mu-, delta-, kappa-OR) mRNA expression was quantified by Northern blot and quantitative RT-PCR, respectively. Isolated cardiac myocytes and non-myocytes from neonatal rat heart were used for cell culture experiments. Results: Overall expression of OR in the heart was markedly lower than in brain tissue, with kappa-OR being the most abundant isoform in the heart. We did not observe differences in kappa-OR expression in ventricular and atrial myocardium. In contrast, delta-OR expression was markedly higher in atria than in ventricles. mu-OR expression in the heart was below the detection limit of the developed qRT-PCR assay. In left ventricular myocardium, ppENK mRNA levels were significantly increased in 2K1C rats but decreased in ISO rats. Cell culture experiments from neonatal rat hearts revealed that myocytes and non-myocytes express ppENK mRNA. In these cells, receptor-dependent and independent stimulation of the beta-adrenergic signalling pathway caused an increase in ppENK mRNA. Furthermore, inactivation of inhibitory G-proteins by pertussis toxin increased basal and noradrenaline-stimulated ppENK mRNA expression. The physiological significance of myocardial opioids was investigated in isolated perfused rat hearts. Opioid receptor antagonists (nor-BNI, naltrindol) and the enkephalinase inhibitor CPL had no effect on contractility but significantly altered atrioventricular conduction. Conclusion: These observations suggest that the cardiac opioid system is activated in cardiac hypertrophy. Pressure overload and stimulation of the beta-adrenergic signalling pathway have been identified as a possible mechanism leading to increased ppENK expression, which may contribute to opioid system activation. Finally, endogenous opioids modulate the dromotropic response to catecholamine stimulation. The latter finding raises the possibility that endogenous opioids may contribute to the pathogenesis of arrhythmias. (C) 2005 European Society of Cardiology. Published by Elsevier B.V, All rights reserved
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
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