1,721,493 research outputs found
Characterization of Ca2+ transients induced by intracellular photorelease of InsP3 in mouse ovarian oocytes.
No full textCa2+ transients (measured with Fluo-3) were induced in single mouse ovarian oocytes by photolytic liberation of InsP3. The time course of cytosolic Ca2+ changes induced in this way is composed of distinct phases: upstroke, fast decline, slow declining plateau and fast decline to rest level. All the phases reflect mainly intracellular redistributions of the ion and not influx, since they are not strongly dependent on external Ca2+ or on changes in transmembrane potential. Often sustained Ca2+ oscillations followed the first InsP3-induced Ca2+ transient. These persisted for several minutes in the absence of external Ca2+. The initial rate of Ca2+ rise and the delay between the InsP3 stimulus and Ca2+ upstroke are correlated with the amount of liberated InsP3. A second InsP3 stimulation, applied during the plateau, causes only small Ca2+ elevations, lacking the upstroke phase. A second, full sized, transient could be elicited only after a complete return to the basal level. Vanadate, applied intracellularly, appeared to inhibit the re-uptake phase into the stores, stabilizing the plateau level. The present observations suggest that in mouse oocytes the InsP3-sensitive stores provide only a small and graded Ca2+ release which may then act as a trigger for a more substantial Ca(2+)-induced Ca2+ release (CICR) process
Routing with Deceptive Information
Full text linkRouting protocols based on the link-state paradigm notoriously suffer from the problem of stale information in highly dynamic traffic scenarios, leading to an overall loss in routing efficiency. Solutions are not easy to come by, since an increase in the frequency of link state advertisements is equally dangerous: route flapping (i.e., periodic route changes that force traffic to be routed through an alternately underloaded set of paths) is one of the main drawbacks. In this paper we propose a novel, yet simple link state mechanism that may deliberately advertise false link state information with the purpose of stabilizing the routing, while keeping a high network utilizatio
P2y purinoceptors in normal NIH 3T3 and in NIH 3T3 overexpressing c-ras
No full textThe ability of purinergic agonists to induce Ca2+ responses has been tested in two lines of murine fibroblasts: normal NIH 3T3 fibroblasts and NIH 115.14, a clone expressing high levels [1] of the c-ras protooncogene. Both kinds of cells are responsive to ATP in the range 1 microM-1 mM; ADP and ATP gamma S are almost as potent as ATP, while AMP is unable to elicit a response. Ca2+ measurements performed in single cells by image analysis show great variability among cells but in each individual responding cell the Ca2+ rise occurs in an all-or-none fashion. The transient Ca2+ response does not depend on influx from the extracellular medium. Electrophysiological experiments reveal the activation of an outward current (at -50 mV) by ATP, probably due to Ca(2+)-activated K+ channels, confirming the absence of a substantial Ca2+ influx. Finally, stimulation by ATP produces a small but significant increase in the production of inositol phosphates. These results indicate that these cell lines possess purinergic receptors which are not integral membrane channels and which are coupled to InsP3 formation and may be therefore classified as P2Y
Cytosolic calcium responses induced by photolytic release of 1,4,5-inositol trisphosphate in single human fibroblasts.
No full textWe have used the whole cell technique to microinject human fibroblasts with either 1,4,5-inositol trisphosphate (InsP3) or 'caged' InsP3, in order to study the mechanisms of transmembrane signalling related to mitogenic stimulations. Cytosolic Ca2+ elevations in response to 1,4,5 InsP3 diffusing from the patch pipette were difficult to detect, while 1,4,5 InsP3, photoreleased after loading the cell with its inactive precursor, was capable of generating not only a single cytosolic Ca2+ rise but sometimes triggered an oscillatory calcium response, similar to that often observed under mitogenic stimulation. We estimated that less than 100 nM InsP3 was sufficient to generate Ca2+ responses. The Ca2+ rise produced by the photoreleased InsP3 could fully activate the K+ channels present in the plasma membrane of human fibroblasts
Cytosolic calcium and membrane conductance in response to platelet-derived growth factor and bradykinin stimulation in single human fibroblasts.
No full textBradykinin (BK) and platelet-derived growth factor (PDGF) act as mitogens and stimulate phosphatidylinositol (PI) turnover in human fibroblasts. By coupling whole-cell electrophysiological measurements with cytosolic Ca2+ determinations using fura-2 microfluorimetry, we have studied the changes in cytosolic calcium and in membrane conductance in single cells following stimulation with BK or PDGF. Both agonists produce variable patterns of response which include: single transient, sustained pulsations, damped oscillations, no response. In all cases, there is a very good temporal correlation between increases in intracellular Ca2+ and membrane current. The cytosolic calcium elevation appears to be insensitive to membrane potential changes, indicating that Ca2+ is released from an intracellular source. The Ca2(+)-activated current is not blocked by 1 microM apamin or by 0.5 mM (+)-tubocurarine; it is instead strongly reduced by 5 mM tetraethylammonium (TEA). We can conclude that BK and PDGF induce very similar early responses in human fibroblasts, and that the variable pattern of response does not depend on the particular mitogen used. The membrane currents are due to a kind of Ca2(+)-activated K+ channels which, according to their voltage-dependence and specific blockers, belong to the "maxi K+" class
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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