1,720,970 research outputs found
Localizzazione funzionale dei canali pacemaker : identificazione molecolare dei canali f nel nodo senoatriale di coniglio : l'interazione proteina-proteina localizza i canali f nei microdomini caveolari e ne modula le proprieta cinetiche e l'espressione in membrana
No full textGrowing evidence indicates that caveolae, specialized membrane microdomains, are important regulators of ion channels. An important function of caveolae is to cluster related proteins in close proximity to facilitate functional interactions. We have previously shown that pacemaker f-channels are localized in caveolin-enriched membrane fractions (Barbuti et al., 2004, Circ Res 94, 1325) and co-immunoprecipitate with the caveolar protein caveolin-3 in sinoatrial tissue. Since a caveolin-interacting sequence is found in the N-terminus of all HCN channel isoforms (WIIHPYSDF), we hypothesized that mutation of this consensus site in the HCN4 isoform, the most abundant in the sinoatrial node, would cause changes of channel properties similar to those caused by caveolar disorganization. We expressed rabbit HCN4 in CHO cells and used various techniques (point mutation, patch clamp, western blot, immunofluorescence) to verify this hypothesis. We mutated tyrosine 259 into a serine (Y259S). The Y259S channels had a V1/2 potential 24.6 mV more positive than that of the WT: -81 ± 2 mV n = 31; Y259S: -56.4 ± 1 mV n = 35). Also, analysis of time constants (tau) showed the presence of a significant rightward shift of activation/deactivation tau curves of mutated channels. Furthermore, the Y259S current density (-14.5 ± 2 pA/pF; n = 43) was significantly lower than WT current density (-53.5 ± 7.1 pA/pF; n = 41) at -125 mV. These data agree with immunofluorescence data showing a weaker HCN4 signal in CHO cells expressing mutated vs WT channels. Interestingly, the Y259S channels localized, like WT channels, to caveolin-enriched membrane fractions and co-immunoprecipitated with caveolin 1. In conclusion, our data show that the Y259S mutation causes changes of HCN4 properties qualitatively similar to, but quantitatively larger than, those reported for caveolae disorganization without affecting channel localization; furthermore this mutation causes a significant reduction of membrane channel density
Mutation of the putative caveolin-interacting sequence of HCN4 channels affects their properties and expression
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Electrophysiological characterization and autonomic modulation of mouse embryonic stem cell-derived cardiomyocytes
No full textLocalization of f-channels to caveolae mediates specific beta(2)-adrenergic receptor modulation of rate in sinoatrial myocytes
No full textbeta(1)- and beta(2)-adrenergic receptors (ARs) coexist in different regions of the heart. The beta(2)/beta(1) expression ratio is higher in the sinoatrial node (SAN) than in atria and ventricles, but the specific contribution of either type of receptor to rate modulation is still not well established. We have recently demonstrated that pacemaker ("funny") f-channels are located in lipid rafts of the rabbit SAN. Since in ventricular myocytes beta(2)-, but not beta(1)-ARs, localize to caveolae, we hypothesized that modulation of f-channels and of pacemaker activity in SAN myocytes is controlled mainly by beta(2)-AR activation. To address this point, we investigated the caveolar localization of proteins by co-immunoprecipitation and immunocytochemistry, and found that f-channels interact with caveolin 3. We also recorded If current and spontaneous activity from SAN myocytes, and found that beta-AR activation by the non-selective agonists isoproterenol and fenoterol shifted the If activation curve similarly (by 6.3 and 5.3 mV) and increased similarly spontaneous rate (by 23.1% and 21.6%, respectively). Specific 2 stimulation had similar effects (4.9 mV shift of the activation curve and 16.9% rate increase), but specific 0 1 stimulation was less effective (1.7 mV shift and 7.2% rate increase). However, after caveolar disorganization by M beta CD (2%), stimulation of beta(1)-ARs was as effective as non-specific -AR stimulation. These data show that specific stimulation of beta(2)-ARZs is the main mechanism by which heart rate is modulated through a positive shift of the If activation curve and that this mechanism requires specific membrane compartmentation
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
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