1,720,976 research outputs found
Glycine-activated whole cell and single channel currents in rat cerebellar granule cells in culture
No full textThe patch clamp technique was used to study whole cell and single channel currents evoked by glycine in cerebellar granule cells in culture. Whole cell concentration response curve gave a K-d value for glycine of 73 mu M and a Hill slope of 1.58. Glycine-activated currents reversed close to the predicted Cl- equilibrium potential. The responses to glycine were antagonized by strychnine and picrotoxin with an IC50 of 58 nM and 172 mu M, respectively. Furthermore. glycine-evoked currents were potentiated by zinc in a dose-dependent way. In outside-out membrane patches, glycine opened channels with conductances of 32, 52, 84 and 96 pS. The most frequently occurring was the 52 pS channel. The single channel current/voltage relationship was linear in the potential range between - 60 and 60 mV. The 52, 84 and 96 pS channels exhibited prolonged openings whereas the 32 pS was characterized by fast (< 10 ms) openings. Open and closed time histograms of the 52 pS channel could be fitted with the sum of two or three exponentials, respectively, whereas burst duration histograms could be fitted with the sum of two exponentials. Glycine current density changed drastically during days in culture, the maximal expression being between day 4 and 7, suggesting that the expression of glycine receptor channels is developmentally regulated
Functional expression of voltage dependent sodium channels in Xenopus oocytes injected with mRNA from neonatal or adult rat brain
No full textThe two electrode voltage clamp technique was used to study voltage-dependent sodium currents (INa) in Xenopus laevis oocytes previously injected with mRNA extracted from adult (A) or neonatal (N, < 5 days old) rat brains. In the presence of niflumic acid (300 μM) to block endogenous Ca2+-activated Cl- currents, depolarizing voltage steps from a holding potential of -100 mV to various voltages elicited in both groups of oocytes fast inward sodium currents which peaked at ∼ 0 mV and then slowly declined to ∼ 75% of the maximum current at +40 mV. At the peak, A INa was significantly larger than N INa (296 ± 59 nA vs. 147 ± 32 nA). Inactivation kinetics of N INa was best fit with one exponential component whereas A INa with two exponential components. A significant difference in the voltage dependence of inactivation was found between A INa or N INa. The values of Vh were -53 ± 0.9 mV or -59.8 ± 0.7 mV for A INa or N INa respectively. The recovery from inactivation was fitted in both groups with two exponential functions (τf and τs) whose values were not significantly different. However the ratio between τf and τs was significantly higher for N INa comparing to A INa (5.7 vs. 2.1). TTX reversibly blocked INa. The IC50 value was 58.2 ± 6.3 nM for A INa and 20.4 ± 2.2 nM for N INa. These results suggest that different isoforms of TTX-sensitive, voltage-dependent sodium channel subunits are functionally expressed, may be in different proportions in oocytes injected with A or N mRNA. © 1995
Spontaneous gaba-mediated synaptic currents in cerebellar granule cells in culture
No full textThe whole-cell configuration of the patch clamp technique was used to characterize the electrophysiological properties of spontaneous GABA-mediated synaptic currents in cerebellar granule cells grown in a low (5 mM) potassium medium. In the presence of kynurenic acid (1 mM), to block the excitatory drive, bicuculline-sensitive synaptic events were recorded. Their amplitude distribution could be fitted by several Gaussians having the same interpeak distance. In tetrodotoxin (TTX, 1 μM) spontaneous miniature events occurred at a lower frequency. Spontaneous currents reversed polarity at 8.17 ± 0.63 mV, a potential close to Eci; the decay phase could be fitted with a single exponential having at - 60 mV a time constant of 48.7 ± 1.5 ms. In low noise recordings, channel closing could be resolved during the decay phase of miniature events. It appeared that a single quantum of GABA opened few channels on the postsynaptic membrane. © Rapid Communications of Oxford Ltd
Functionally distinct chloride-mediated GABA responses in rat cerebellar granule cells cultured in a low potassium medium
No full textThe patch-clamp technique was used to study whole cell currents evoked by gamma-aminobutyric acid (GABA) in rat cerebellar granule cells cultured in 5 mM potassium, a condition that favors the development of functional GABAergic synapses. GABA activated both high- and low-sensitivity receptors. The high-sensitivity receptor had an effective concentration producing half the maximum response (EC(50)) of 13 mu M, whereas the low-sensitivity one had an EC(50) of 255 mu M. The GABAA receptor agonist isoguvacine activated only the high-sensitivity receptor with an EC(50) of 16 mu M. When GABA was applied during the desensitized phase of the response elicited by a saturating concentration of isoguvacine, it was still able to induce a small response, whereas when isoguvacine was applied during the desensitizing phase of GABA-evoked current no response was detected. GABA responses were highly heterogeneous regarding their sensitivity to bicuculline. In a small number of cells (3 of 25), bicuculline (10 mu M) completely abolished GABA-evoked currents. In the majority of the neurons (22 of 25) the blocking effect of bicuculline (100 mu M) was 64 +/- 4% (mean +/- SE). The bicuculline-resistant component was abolished by picrotoxin (100 mu M). In bicuculline, the dose-response curve for GABA was fitted with a sigmoidal curve with an EC(50) value of 209 mu M. These data indicate that functional new GABA receptor types with unusual pharmacology could be switched on by conditions that maintain cells in their undifferentiated state
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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