1,720,984 research outputs found
Progesterone inhibits capacitative Ca2+ entry in Jurkat T lymphocytes by a membrane delimited mechanism, independently of plasma membrane depolarization
No full textThe non-genomic inhibitory effect of progesterone on capacitative calcium entry was studied in Jurkat T lymphocytes. Capacitative calcium entry was induced by depleting intracellular calcium stores with thapsigargin and evaluated by a calcium free/calcium readmission protocol, in Fura-2 loaded cells. Progesterone (10-40 microg/ml) inhibited calcium entry and concomitantly depolarized cells, as revealed by measuring the plasma membrane potential with the fluorescent probe bis-oxonol. However, experiments run under depolarizing conditions (i.e. by substituting for Na+ with K+ ions in the medium) revealed that progesterone (10-40 microg/ml) could inhibit capacitative calcium entry independently of plasma membrane depolarization. The direct inhibition of calcium entry by progesterone was: (i) reverted by a treatment suitable to remove progesterone bound to cell surface, (ii) apparently related to the extent of membrane bound progesterone (measured radioisotopically), and (iii) specific, in that other related steroid compounds did not inhibit calcium entry
Permeability of liver microsomal membranes to glucose
No full textThe permeability of rat liver microsomes to glucose has been studied by using 14C-labelled D-glucose and a light-scattering technique. 1) The microsomal intravesicular apparent isotope space for D-glucose (1 mM; after 5 min incubation at 22°C) was 2.34 μl/mg protein, i.e., approximately 72% of the apparent water space. 2) Efflux of [14C]D-glucose from microsomal vesicles pre-loaded as in 1) and measured by rapid Millipore filtration after dilution (100 fold) in a glucose-free medium revealed that 15 sec after dilution only 15% of intravesicular glucose was still retained by microsomes. 3) Osmotic behaviour of microsomes upon addition of D-glucose measured by a light-scattering technique revealed a glucose influx, saturable at [D-glucose] ≥ 100 mM, and (partially) inhibited by pentamidine and cytochalasin B. Ascorbic acid, L-glucose and other monosaccharides and related compounds also permeated liver microsomes in a fashion similar to D-glucose. These data indicate the existence of a facilitative transport system(s) for glucose in the membrane of liver endoplasmic reticulum vesicles
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
Both translocon and a cation channel are involved in the passive Ca2+ leak from the endoplasmic reticulum: a mechanistic study on rat liver microsomes
No full textSteady-state levels of calcium ions in endoplasmic reticulum reflect a balance between active inward transport, mediated by MgATP-dependent Ca2+ pumps, and passive backflux of the ions, through putative "leak channels". We have investigated the efflux of Ca2+ from rat liver microsomal vesicles, passively pre-equilibrated in the presence radiolabelled Ca. Similarly, we have also evaluated the efflux of a low-Mwt uncharged compound, i.e., sucrose. The results show that two major passive Ca2+ efflux pathways exist. One appeared to involve the translocon pore, since it was stimulated by the translocon opener puromycin, and also allowed the passage of sucrose. Putative channels likely mediated the other one, since it required counter ion influx and was inhibited by Gd3+ and La3+. The latter pathway did not appear to involve inactive Ca2+ pumps, Bcl2 proteins, or known channels, such as the InsP3 and ryanodine receptors. While sucrose efflux was highly represented in a rough microsomal subfraction-enriched in the translocon component Sec61 alpha--the efflux of Ca2+ was represented both in smooth and in rough microsomes. We conclude that the passive efflux of Ca2+ from the (liver) ER could be mediated by both the translocon pore and putative Ca2+ leak channels. However, the relative role of these Ca2+ efflux pathways in the intact cell as well as the molecular nature of the Ca2+ leak channel(s) remain to be clarified
CoA and fatty acyl-CoA derivatives mobilize calcium from a liver reticular pool
Full text linkThe effect of CoA and fatty acyl-CoA esters on Ca2+ fluxes has been studied in isolated liver microsomes and in digitonin-permeabilized hepatocytes. When microsomes were loaded with increasing concentrations of Ca2+ (6-29 nmol/mg of protein), the extent to which CoA and palmitoyl-CoA released Ca2+ increased. At 23 nmol of Ca2+/mg of protein, half-maximal [CoA] and [palmitoyl-CoA] were 35 and 50 μM respectively. Under conditions of minimal Ca2+ loading, net release of Ca2+ was absent, but Ca2+ translocation from a CoA-sensitive to a CoA-insensitive pool took place. The effect of CoA required the presence of fatty acids, probably to form fatty acyl esters. In permeabilized hepatocytes, the pool(s) mobilized by CoA (or by palmitoyl-CoA) appeared to be different from that mobilized by Ins(1,4,S)P3
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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