1,720,963 research outputs found
STRUCTURAL AND FUNCTIONAL-ASPECTS OF CALCIUM HOMEOSTASIS IN EUKARYOTIC CELLS
No full textThe maintenance of a low cytosolic free-Ca2+ concentration, ([Ca2+]i) is a common feature of all eukaryotic cells. For this purpose a variety of mechanisms have developed during evolution to ensure the buffering of Ca2+ in the cytoplasm, its extrusion from the cell and/or its accumulation within organelles. Opening of plasma membrane channels or release of Ca2+ from intracellular pools leads to elevation of [Ca2+]i; as a result, Ca2+ binds to cytosolic proteins which translate the changes in [Ca2+]i into activation of a number of key cellular functions. The purpose of this review is to provide a comprehensive description of the structural and functional characteristics of the various components of [Ca2+]i homeostasis in eukaryotes
Role of the purinergic P2Z receptor in spontaneous cell death in J774 macrophage cultures
No full textJ774 mouse macrophages express an ionotropic receptor gated by extracellular ATP. Activation of this receptor, currently named purinergic P2Z, causes transmembrane ion fluxes, plasma membrane depolarization, cell swelling and eventual cell death. The physiological role of this receptor is as yet unknown. In the present report we show that macrophage cell clones that hypo-express the P2Z receptor showed a very low degree of spontaneous cell death in culture, while hyper-expressing clones were exceedingly susceptible to cell death. To further support a role for ATP receptors in spontaneous cell death, addition to the macrophage cell cultures of oxidized ATP, a selective inhibitor of ionotropic purinergic receptors, or the ATP-hydrolysing enzyme apyrase, also reduced spontaneous death
Responses of mouse lymphocytes to extracellular ATP. II Extracellular ATP causes cell type-dependent lysis and DNA fragmentation
Full text linkExtracellular ATP (ATPo) caused dose-dependent lysis of YAC-1 and P-815 mouse tumor cells. This event, assessed by 51Cr release, was accompanied by sustained depolarization of the plasma membrane potential and Ca2+ influx. Plasma membrane depolarization and Ca2+ influx occurred within a few seconds of ATPo addition to both cell types, whereas 51Cr was released without apparent lag in YAC-1 cells and after 2 h in P-815 cells. Furthermore, a rise in [Ca2+]i was required for ATPo-dependent lysis of YAC-1 but not P-815 cells. In P-815 cells, ATPo caused an early and [Ca2+]i-independent DNA fragmentation that occurred at lower nucleotide concentrations than those required to trigger 51Cr release. Instead in YAC-1 cells very low concentrations of ATPo caused early lysis (ED50 for lysis about 200 microM) accompanied by only barely detectable DNA fragmentation. Previous studies disclosed that lymphokine-activated killer cells are fully resistant to the membrane-perturbing effects of ATPo. We show that lymphokine-activated killer cells also do not undergo DNA fragmentation even in the presence of high ATPo concentrations. This study complements previous observations on the lytic effects of ATPo and shows that this nucleotide can also cause DNA fragmentation, one of the earliest target cell alterations observed during CTL-mediated lysis
Cell membrane receptors for extracellular ATP: a new family of apoptosis-signalling molecules
No full text
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
CHARACTERIZATION OF THE CYTOTOXIC EFFECT OF EXTRACELLULAR ATP IN J774-MOUSE MACROPHAGES
No full textExtracellular ATP (ATPo) is known to be cytotoxic to many cell types through a mechanism which is largely unknown. Very recently this nucleotide has been shown to cause cell death by apoptosis, probably by interacting with specific cell-surface receptors. In the present study we have investigated the mechanism of ATPo-dependent cytotoxicity in the macrophage-like mouse cell line J774. It has been previously reported that in this cell type ATPo activates trans-membrane Ca2+ and Na+ fluxes and a drastic increase in the plasma-membrane permeability to hydrophilic solutes smaller than 900 Da. These changes are followed by cell swelling and lysis. We show in the present study that, although this nucleotide triggers a rise in the cytoplasmic Ca2+ concentration, neither cell swelling nor lysis is Ca(2+)-dependent. Furthermore, cell lysis is not dependent on Na+ influx, as it is not prevented by iso-osmotic replacement of extracellular Na+ with choline or N-methylglucamine. On the contrary, ATPo-dependent cytotoxicity, but not the ATPo-dependent increase in plasma-membrane permeability, is completely abrogated in sucrose medium. Under our experimental conditions ATPo does not cause DNA fragmentation in J774 cells. We conclude from these findings that ATPo does not cause apoptosis of J774 macrophages and promotes a Ca(2+)- and Na(+)-independent colloido-osmotic lysis
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
- …
