1,721,182 research outputs found
Una nuova stazione di Cephalaria mediterranea (Viv.) Szabò nella Sardegna Sud-occidentale
No full textCon questa segnalazione gli autori precisano la
distribuzione in Sardegna di Cephalaria mediterranea (Viv.)
Szabò con il ritrovamento di una nuova stazione nel
Fluminese (Sardegna Sud-occidentale). Si apportano ulteriori
precisazioni di carattere ecologico di questo endemismo
sardo-corso
Ligand induced internalization of CD38 results in intracellular Ca2+ mobilization. role of NAD+ transport across cell membranes
No full textCD38, a transmembrane glycoprotein
widely expressed in vertebrate cells, is a bifunctional
ectoenzyme catalyzing the synthesis and hydrolysis of
cyclic ADP-ribose (cADPR). cADPR is a universal
second messenger that releases calcium from intracellular
stores. Since cADPR is generated by CD38 at
the outer surface of many cells, where it acts intracellularly,
increasing attention is paid to addressing
this topological paradox. Recently, we demonstrated
that CD38 is a catalytically active, unidirectional
transmembrane transporter of cADPR, which then
reaches its receptor-operated intracellular calcium
stores. Moreover, CD38 was reported to undergo a
selective and extensive internalization through non
clathrin-coated endocytotic vesicles upon incubating
CD381 cells with either NAD1 or thiol compounds:
these endocytotic vesicles can convert cytosolic NAD
into cADPR despite an asymmetric unfavorable orientation
that makes the active site of CD38 intravesicular.
Here we demonstrate that the cADPR-generating
activity of the endocytotic vesicles results in
remarkable and sustained increases of intracellular
free calcium concentration in different cells exposed
to either NAD1, or GSH, or N-acetylcysteine. This
effect of CD38-internalizing ligands on intracellular
calcium levels was found to involve a two-step mechanism:
1) influx of cytosolic NAD1 into the endocytotic
vesicles, mediated by a hitherto unrecognized
dinucleotide transport system that is saturable, bidirectional,
inhibitable by 8-N3-NAD1, and characterized
by poor dinucleotide specificity, low affinity,
and high efficiency; 2) intravesicular CD38-catalyzed
conversion of NAD1 to cADPR, followed by outpumping
of the cyclic nucleotide into the cytosol and
subsequent release of calcium from thapsigarginsensitive
stores. This unknown intracellular trafficking
of NAD1 and cADPR based on two distinctive
and specific transmembrane carriers for either nucleotide
can affect the intracellular calcium homeostasis
in CD381 cells.—Zocchi, E., Usai, C.,
Guida, L., Franco, L., Bruzzone, S., Passalacqua, M.,
De Flora, A. Ligand-induced internalization of CD38
results in intracellular Ca21 mobilization: role of
NAD1 transport across cell membranes. FASEB J. 13,
273–283 (1999
Diadenosine homodinucleotide products of ADP-ribosyl cyclase behave as modulators of the purinergic receptor P2X7
No full textADP-ribosyl cyclases from both vertebrates and invertebrates were previously shown to produce two isomers of P1,P2 diadenosine 5',5'"-P1, P2-diphosphate, P18 and P24, from cyclic ADP-ribose (cADPR) and adenine. P18 and P24 are characterized by an unusual N-glycosidic linkage in one of the adenylic mononucleotides (Basile, G., Taglialatela-Scafati, O., Damonte, G., Armirotti, A., Bruzzone, S., Guida, L., Franco, L., Usai, C., Fattorusso, E., De Flora, A., and Zocchi, E. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 14509-14514). P24, but not P18, proved to increase the intracellular Ca(2+) concentration ([Ca(2+)](i)) in HeLa cells and to negatively affect mitochondrial function. Here we show that micromolar P24, but not P18, triggers a slow and sustained influx of extracellular Ca(2+) through the opening of the purinergic receptor/channel P2X7. On the other hand, P18 inhibits the Ca(2+) influx induced by 0.6 mm ATP in HEK293 cells stably transfected with P2X7, with an IC(50) of approximately 1 mum. Thus, P18 is devoid of intrinsic P2X7 stimulatory activity and behaves as an ATP antagonist. A P2X7-mediated increase of the basal [Ca(2+)](i) has been demonstrated to negatively affect Schwann cell (SC) function in rats with the inherited, peripheral neuropathy Charcot-Marie-Tooth 1A (CMT1A) (Nobbio, L., Sturla, L., Fiorese, F., Usai, C., Basile, G., Moreschi, I., Benvenuto, F., Zocchi, E., De Flora, A., Schenone, A., and Bruzzone S. (2009) J. Biol. Chem. 284, 23146-23158). Preincubation of CMT1A SC with 200 nm P18 restored the basal [Ca(2+)](i) to values similar to those recorded in wild-type SC. These results identify P18 as a new P2X7 antagonist, potentially useful in the treatment of CMT1A
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
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