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Phosphatidylserine vesicles increase Ca2+ uptake by rat brain synaptosomes.
No full textPhosphatidylserine (PS) vesicles incorporated into rat brain synaptosomes increased total Ca2+ uptake. Total Ca2+ uptake was resolved in three components: K+ depolarization-induced Ca2+ uptake, Na+/Ca2+ exchange, and passive Ca2+ entry, which were differently affected by PS depending on the amount of incorporated phospholipid. K+ depolarization-induced Ca2+ uptake was stimulated by 0.05-0.10 mumol PS/mg protein while 0.10-0.30 mumol PS/mg protein increased Na+/Ca2+ exchange activity and passive Ca2+ entry but not K+ depolarization-induced Ca2+ uptake. High amounts of incorporated PS also increased passive Rb+ uptake
Inhibition of the Na+/Ca2+ exchange in cardiac sarcolemmal vesicles by amiloride.
No full textThe pyrazine diuretic amiloride inhibits the Na+/Ca2+ exchange activity of cardiac sarcolemmal vesicles in a concentration-dependent way. A good relationship between the uptake of amiloride by the vesicles and the inhibition of the exchanger has been found. Kinetic analyses indicate that the inhibition of Na+/Ca2+ exchange activity by amiloride is non-competitively removed by Ca2+ and competitively overcome by an outwardly directed Na+ gradient
Effects of N-chlorobenzyl analogues of amiloride on myocardial contractility, Na-Ca-exchange carrier and other cardiac enzymatic activities.
No full text1. In electrically driven guinea pig left atria, micromolar concentrations (2 mumol/l to 80 mumol/l) of N-chlorobenzyl derivatives of amiloride (o-chlorobenzamil and 3',4'-dichlorobenzamil) produced quantitatively similar positive inotropic effects. Contracture developed with 3',4'-dichlorobenzamil. Endogenously released catecholamines contributed 30% to the positive inotropic effect of o-chlorobenzamil but did not contribute at all to the effect of 3',4'-dichlorobenzamil. When tested in the presence of the inhibitor of phosphodiesterase isobutylmethylxanthine, o-chlorobenzamil antagonized its positive inotropic effect, whereas 3',4'-dichlorobenzamil potentiated it. o-Chlorobenzamil also antagonized the positive inotropic effect of ouabain in that it shifted its concentration-effect curve to the right. Moreover, o-chlorobenzamil prevented the appearance of ouabain toxicity in terms of a rise in the resting force. 2. Also, in electrically driven guinea pig papillary muscle, micromolar concentrations (5 mumol/l to 30 mumol/l) of both N-chlorobenzyl derivatives of amiloride produced a positive inotropic effect. This effect was more marked with 3',4'-dichlorobenzamil than with o-chlorobenzamil and was associated for both compounds with lengthening of relaxation time. 3. o-Chlorobenzamil and 3',4'-dichlorobenzamil influenced, though not to the same extent, several systems involved in the onset and in the control of cardiac contractility. 3',4'-Dichlorobenzamil inhibited with the same potency Na-K-ATPase, sarcotubular Ca-ATPase, Na-Ca-exchange carrier, cAMP-dependent phosphodiesterase isolated from bovine heart and oxidative phosphorylation of mitochondria isolated from rat liver. Low micromolar concentrations of o-chlorobenzamil mainly inhibited Na-Ca-exchange carrier and cAMP-dependent phosphodiesterase.(ABSTRACT TRUNCATED AT 250 WORDS
Inhibition of Na+/Ca2+ exchange by amiloride acting from opposite sides of cardiac sarcolemma.
No full textAmiloride inhibited the Na+Ca2+ exchange activity of cardiac sarcolemmal vesicles with similar affinities at the cis and trans sides of the membrane, estimated apparent Ki on both sides of the sarcolemma being similar. The extent of amiloride inhibition on Na+/Ca2+ exchange activity was decreased by alkaline pH only when the drug was acting from the external side of the vesicle sarcolemma, whereas when vesicles were preincubated with the drug at different pH values, amiloride appeared to act as a weak permeant base, being a more effective inhibitor at alkaline pH values. In fact, a rise in the pH of the preincubation medium may favour the entry and consequently the effect of the drug on the exchanger. The pH dependence of the inhibition of Na+/Ca2+ exchange activity by either extravesicular or intravesicular amiloride was consistent with the hypothesis that in both cases the protonated drug was the active form. Evidence is presented that the pattern of interaction of amiloride on the Na+/Ca2+ exchange system strictly depended on the sidedness of drug action. In fact, while Na+ protected against inhibition by amiloride when it was acting on the same side of the vesicle membrane as the drug, it synergically interacted with amiloride to inhibit exchange activity when it was acting on the opposite side of the sarcolemma as the drug. Furthermore, only extravesicular amiloride removed the stimulation of Na+/Ca2+ exchange activity in Ca2+-treated 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
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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