1,721,002 research outputs found
Mechanisms of modulation by internal protons of cyclic nucleotide-gated channels cloned from sensory receptor cells
No full textWe have examined the modulation by internal protons of cyclic nucleotide-gated (CNG) channels cloned from bovine olfactory receptor cells and retinal rods. CNG channels Mere studied in excised inside-out membrane patches from Xenopus laevis oocytes previously injected with the mRNA encoding for the subunit 1 of olfactory or rod channels. Channels were activated by cGMP or cAMP, and currents as a function of cyclic nucleotide concentrations were measured as pH(i) varied between 7.6 and 5.0. Increasing internal proton concentrations caused a partial blockage of the single-channel current, consistent with protonation of a single acidic site with a pK(i) of 4.5-4.7, both in rod and in olfactory CNG channels. Channel gating properties were also affected by internal protons. The open probability at law cyclic nucleotide concentrations was greatly increased by lowering pH(i), and the increase was larger when channels were activated by cAMP than by cGMP. Therefore, internal protons affected both channel permeation and gating properties, causing a reduction in single-channel current and an increase in open probability. These effects are likely to be caused by different titratable groups on the channel
The permeability of the cGMP-activated channel to organic cations in retinal rods of the tiger salamander
No full text1. The permeability of the channel activated by guanosine 3',5'‐cyclic monophosphate (cGMP) to many organic monovalent cations was determined by recording macroscopic currents in excised inside‐out patches of plasma membrane from isolated retinal rod outer segments of the tiger salamander. 2. Current‐voltage relations were measured when the NaCl of the bathing medium was replaced by salts of organic cations. Permeability ratios relative to Na+ ions were calculated with the Goldman‐Hodgkin‐Katz potential equation from the measured changes of reversal potentials. 3. Hydroxylammonium+, hydrazinium+ and methylammonium+, which are molecules of very similar shape and size, permeate the channel with very different permeability ratios: 5.92, 1.99 and 0.60 respectively. 4. Methylated and ethylated ammonium+ compounds were investigated. It was found that, not only methylammonium+, but also dimethylammonium+ and ethylammonium+ were permeant with permeability ratios of 0.6, 0.14 and 0.16 respectively. Trimethylammonium+, tetramethylammonium+, diethylammonium+, triethylammonium+, and tetraethylammonium+ were not permeant. 5. Guanidinium+ and its derivatives formamidinium+, aminoguanidinium+, acetamidinium+ and methylguanidinium+ were all permeant with permeability ratios 1.12, 1.00, 0.63, 0.36 and 0.33 respectively. 6. The cGMP‐activated channel was found to be permeable to at least thirteen organic cations. Molecular models of the permeant cations indicate that the cross‐section of the narrowest part of the pore must be at least as large as a rectangle of 0.38 x 0.5 nm dimensions
The relation between stimulus and response in isolated olfactory receptor cells of the tiger salamander
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
The effects of parafunctional contacts on the natural dentition
No full textThe paper analyses the incidence and etiology of bruxism through a review of the literature. The effects that this pathology has on teeth are discussed and there is a brief discussion of therapy
Occlusion in the etiology of craniomandibular disorders. Current directions
No full textCraniomandibular disorders are a pathology with a multifactorial genesis where the aetiological aspects it represented by emotional and occlusal factors. These provoke muscular hyperactivity so determining a change in all components of the stomatognathic apparatus. A critical analysis of the literature leads to an analysis of the importance of the occlusal factor in the aetiology of MCD. The conclusions reached are that the ideal occlusion is a theoretical concept. Physiological occlusion is the situation in which, independently of the number, lay-out and relationship between teeth there exists a subjective occlusal stability and a satisfactory masticatory, phonatory and aesthetic function
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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