1,720,975 research outputs found
Effects of semistarvation on transintestinal d-glucose transport and d-glucose uptake in brush border and basolateral membranes of rat enterocytes
No full textThe present work shows that semistarvation (8-10 g of food for 10 days) increases net d-glucose, Na+ and water transport in the everted and perfused rat jejunum. A lincar and positive correlation between cell sugar concentration and transport was found in control and semistarved rats, but the phenomenon was more relevant only in semistarved animals. Membrane vesicle experiments showed that semistarvation increases sugar overshoot only in brush border membrane vesicles, while this situation does not occur in basolateral membrane vesicles. The effect of partial food deprivation seems to enhance net sugar transport by mereasing sugar entry across the apical membrane of enterocytes
A creatine transporter is operative at the brush border level of the rat jejunal enterocyte
No full textAlthough ergogenic effects and health benefits have been reported for creatine used as nutritional supplement, to date little is known about the mechanism of creatine absorption in the small intestine. Thus the current study was undertaken to elucidate the mechanism of creatine intake in rat jejunum with the use of well-purified brush border membrane vesicles, isolated from jejunal enterocyte. Creatine uptake was found markedly stimulated by inwardly directed Na+ and Cl- gradients, potential-sensitive, strongly reduced by the substitution of Na+ and Cl- with various cations and anions and positively affected by intravesicular K+. Moreover creatine uptake is: 1) significantly inhibited by creatine stuctural analogs, 2) abolished by low concentrations of MTSEA, 3) saturable as a function of creatine concentration with an apparent Michaelis-Menten costant of 24.08 ± 0.80 mM and a maximal velocity of 391.30 ± 6.19 pmoles mg protein-1 30 s-1. The transport is electrogenic since at least two Na+ and one Cl- are required to transport one creatine molecule. Western blot analysis showed the same amount of creatine transport protein in the jejunal apical membrane when compared to ileum.
Thus these data demonstrate the existence of a Na+- and Cl--dependent, PD-sensitive, electrogenic carrier-mediated mechanism for creatine absorption in rat jejunal apical membrane vesicles, which is biochemically and pharmacologically similar to those observed in other tissues. However in other cell types the stimulatory effect of intravesicular K+ was never detected
Intestinal sugar transport during ageing
No full textAgeing effects on sugar intestinal transport were studied by using the everted sac and the brush-border membrane vesicle techniques. Four age groups of rats were used: very young, young, adult and old animals. Net transintestinal transport of d-glucose and intracellular sugar accumulation were greater in young than in very young, adult and old rats. Net Na+ transport was high in very young and young animals and then it declined with age. In brush-border membrane vesicle experiments d-glucose overshoot was smaller in the groups of animals where net sugar transport was less. In old rats, however, the overshoot did not occur. Short-circuiting of vesicles with valinomycin showed that the driving forces for sugar accumulation, i.e. the chemical potential gradient of Na+ and the electrical potential gradient, played different roles during ageing. In very young animals the chemical potential gradient seems to be responsible for d-glucose overshoot; in young rats both gradients are important while in adult animals the electrical potential gradient represents the main driving force
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
Intestinal absorption of carbohydrates
No full textNet transintestinal transport of D-glucose (Gl) and 3-0-methyl-D-glucose (3MG) in four classes of rats (very young, young, adult and old) was studied both “in vitro” and “in vivo”. D-glucose uptakes into brush border membrane vesicles (BBMV) were also determined. “In vitro” experiments were performed on everted sac of jejunum and on BBMV by using a rapid filtration technique. “In vivo” studies were carried out on the same intestinal tract perfused “in situ”. The main results obtained were the following: i) “in vitro” net transintestinal transport of Gl was higher in young rats than in very young and adult animals but much lower in aged rats. Gl uptake into BBMV showed the same pattern. The presence of valinomycin reduced Gl uptake in young animals and abolished it in adult rats. Surprisingly, old animals did not show any overshoot in both control and valinomycin-treated vesicles. ii) Net transintestinal 3MG transport “in vitro” was similar in the first three groups of animals and decreased only in old rats. iii) “In vivo” experiments showed a similar transport of 3MG in all groups of animals but a reduced transport of Gl only in aged animals. The volume of the enterocytes of old rats was consistently lower both in “in vitro” and “in vivo” experiments. Valinomycin studies indicated that the electrical properties of BBMV affected sugar uptake differently in the various ages of animals. Moreover, it seemed that old rats did not present a Na+-dependent uptake since there was no overshoot and the pattern of Gl uptake was similar when Na+ or K+ were present in the incubation medium. “In vivo” experiments showed a decreased transport of Gl only in old rats. This seems to indicate that in “in vivo” conditions other factors can influence Gl transport since this sugar, unlike 3MG, showed different transport rates in the four groups of animals during “in vitro” studies
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