1,721,018 research outputs found
The P2 receptors in platelet function
No full textAfter vessel wall injury, platelets adhere to the exposed subendothelium, are activated, and release mediators such as thromboxane A2 (TXA 2) and nucleotides stored at very high concentration in the so-called dense granules. Among other soluble agents, released nucleotides act in a positive feedback mechanism to cause further platelet activation and amplify platelet responses induced by agents such as thrombin or collagen. Adenine nucleotides act on platelets through three distinct P2 receptors: two are G protein-coupled adenosine diphosphate (ADP) receptors, namely the P2Y 1 and P2Y12 receptor subtypes; the P2X1 receptor ligand-gated cation channel is activated by adenosine triphosphate (ATP). The P2Y1 receptor initiates platelet aggregation but is not sufficient for a full platelet aggregation in response to ADP, whereas the P2Y12 receptor is responsible for completion of the aggregation to ADP. This receptor, the molecular target of the antithrombotic drug clopidogrel, is responsible for most of the potentiating effects of ADP when platelets are stimulated by agents such as thrombin, collagen, or immune complexes. The P2X1 receptor is involved in platelet shape change and in activation by collagen under shear conditions. Each of these receptors is coupled to specific signal transduction pathways in response to ADP or ATP and is differentially involved in all of the sequential events involved in platelet function and hemostasis. As such, they represent potential targets for antithrombotic drugs. Copyrigh
ADP receptors and clinical bleeding disorders
No full textADP plays a key role in hemostasis and thrombosis. Despite its early identification in 1961 as the first known aggregating agent, the molecular basis of ADP-induced platelet activation is only beginning to be understood. The present review proposes a model of 3 purinergic receptors contributing separately to the complex process of ADP-induced platelet aggregation: the P2X1 ionotropic receptor, responsible for rapid influx of ionized calcium into the cytosol; the P2Y1 metabotropic receptor, responsible for mobilization of ionized calcium from internal stores, which initiates aggregation; and an as-yet-unidentified P2Y receptor coupled to G(αi2), which is essential for the full aggregation response to ADP. It is probable that this as-yet-unidentified receptor is the molecular target of the ADP- selective antiaggregating drugs ticlopidine and clopidogrel. In addition, it is probably defective in patients with a bleeding diathesis that is characterized by selective impairment of platelet responses to ADP
Platelets from a patient heterozygous for the defect of P2(CYC) receptors for ADP have a secretion defect despite normal thromboxane A(2) production and normal granule stores - Further evidence that some cases of platelet 'primary secretion defect' are heterozygous for a defect of P2(CYC) receptors
No full textTo the editor: Adenosine diphosphate (ADP) does not induce thromboxane A(2) generation in human platelets
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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
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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