1,720,988 research outputs found
Zinc uptake in human seminal spermatozoa: characterization and effects on cell membranes.
No full textHuman ejaculated spermatozoa take up zinc in a time- and concentration-dependent manner. The kinetics of 65Zn2+ uptake is suggestive of an at least partly carrier-mediated transport. The lack of effect of the respiratory chain inhibitor antimycin A could mean that mitochondrial ATP is not required as an energy source for the uptake. The failure of nonpermeant SH reagent mersalyl to modify zinc uptake indicates that functional membrane sulfhydryl groups are not involved in the process. A dose-dependent inhibition of 65Zn2+ uptake was induced by the "anticalmodulin" drug trifluoperazine, suggesting that the calcium-binding protein calmodulin could have a role in zinc transport. In in vitro experiments this cation brought about a powerful effect in protecting the spermatozoa from being damaged by hypo-osmosi
Identification of calcitonin receptors in human spermatozoa.
No full textCalcitonin (CT) is a powerful hypocalcemic hormone which regulates calcium balance in cells. The presence of CT and CT receptors has been demonstrated in many extrathyroidal tissues, including the male genital tract. CT immunoreactivity has also been found in human seminal fluid, and an inhibitory effect of salmon CT on human sperm motility in vitro was recently reported. In this study the presence of specific binding sites for synthetic salmon CT in intact human spermatozoa was investigated using [125I]salmon CT. Binding experiments demonstrated a CT-sperm interaction involving a receptor-mediated mechanism. The binding was very rapid and minimally reversible, with the maximal site saturation occurring at approximately 2 nM labeled peptide. The dissociation of the CT-receptor complex was only slightly influenced by the addition of unlabeled hormone. Increasing concentrations of unlabeled salmon, eel, and human CT produced a dose-dependent inhibition of [125I]salmon CT binding. These data fulfill the major criteria for demonstration of specific receptors for salmon CT in human spermatozoa. Owing to the key role of calcium ions in regulating sperm motility and the onset of the acrosomal reaction, CT receptors could be important in male gamete physiology
Italian pilot study for an extenal quality control scheme in semen analysis and antisperm antibodies detectionInt.
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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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