1,721,037 research outputs found
oocytes
No full text1The accessory β subunits of voltage-dependent Ca2+ channels (VDCCs) have been shown to regulate their biophysical properties and have also been suggested to antagonise the G protein inhibition of N-type (α1B), P/Q-type (α1A) and α1E channels. Here we have examined the voltage-dependent involvement of the four neuronal isoforms (β1b, β2a, β3 and β4) in the process of G protein modulation of α1B Ca2+ channels.2All β subunits hyperpolarised α1B current activation, and all antagonised the G protein-mediated depolarisation of current activation. However, except in the case of β2a, there was no generalised reduction by β subunits in the maximal extent of receptor-mediated inhibition of α1B current.3In addition, all VDCC β subunits enhanced the rate of current facilitation at +100 mV, for both receptor-mediated and tonic modulation. The rank order for enhancement of facilitation rate was β3 > β4 > β1b > β2a. In contrast, the amount of voltage-dependent facilitation during tonic modulation was reduced by β subunit co-expression, despite the fact that the apparent Gβγ dissociation rate at +100 mV was enhanced by β subunits to a similar level as for agonist-induced modulation.4Our data provide evidence that G protein activation antagonises Ca2+-channel β subunit-induced hyperpolarisation of current activation. Conversely, co-expression of all β subunits increases the apparent Gβγ dimer dissociation rate during a depolarising prepulse. This latter feature suggests the co-existence of bound Ca2+-channel β subunits and Gβγ dimers on the α1B subunits. Future work will determine how the interaction between Gβγ dimers and Ca2+-channel β subunits with α1B results in a functional antagonism at the molecular level
The Upregulation of α2δ-1 Subunit Modulates Activity-Dependent Ca2+ Signals in Sensory Neurons.
No full textAs auxiliary subunits of voltage-gated Ca(2+) channels, the α2δ proteins modulate membrane trafficking of the channels and their localization to specific presynaptic sites. Following nerve injury, upregulation of the α2δ-1 subunit in sensory dorsal root ganglion neurons contributes to the generation of chronic pain states; however, very little is known about the underlying molecular mechanisms. Here we show that the increased expression of α2δ-1 in rat sensory neurons leads to prolonged Ca(2+) responses evoked by membrane depolarization. This mechanism is coupled to CaV2.2 channel-mediated responses, as it is blocked by a ω-conotoxin GVIA application. Once initiated, the prolonged Ca(2+) transients are not dependent on extracellular Ca(2+) and do not require Ca(2+) release from the endoplasmic reticulum. The selective inhibition of mitochondrial Ca(2+) uptake demonstrates that α2δ-1-mediated prolonged Ca(2+) signals are buffered by mitochondria, preferentially activated by Ca(2+) influx through CaV2.2 channels. Thus, by controlling channel abundance at the plasma membrane, the α2δ-1 subunit has a major impact on the organization of depolarization-induced intracellular Ca(2+) signaling in dorsal root ganglion neurons
Human neuronal stargazin-like proteins, gamma(2), gamma(3) and gamma(4); an investigation of their specific localization in human brain and their influence on Ca(V)2.1 voltage-dependent calcium channels expressed in Xenopus oocytes
No full textBackground: Stargazin (gamma(2)) and the closely related gamma(3), and gamma(4) transmembrane proteins are part of a family of proteins that may act as both neuronal voltage-dependent calcium channel (VDCC) gamma subunits and transmembrane alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproponinc (AMPA) receptor regulatory proteins (TARPs). In this investigation, we examined the distribution patterns of the stargazin-like proteins gamma(2), gamma(3), and gamma(4) in the human central nervous system (CNS). In addition, we investigated whether human gamma(2) or gamma(4) could modulate the electrophysiological properties of a neuronal VDCC complex transiently expressed in Xenopus oocytes.Results: The mRNA encoding human gamma(2) is highly expressed in cerebellum, cerebral cortex, hippocampus and thalamus, whereas gamma(3) is abundant in cerebral cortex and amygdala and gamma(4) in the basal ganglia. Immunohistochemical analysis of the cerebellum determined that both gamma(2) and gamma(4) are present in the molecular layer, particularly in Purkinje cell bodies and dendrites, but have an inverse expression pattern to one another in the dentate cerebellar nucleus. They are also detected in the interneurons of the granule cell layer though only gamma(2) is clearly detected in granule cells. The hippocampus stains for gamma(2) and gamma(4) throughout the layers of the every CA region and the dentate gyrus, whilst gamma(3) appears to be localized particularly to the pyramidal and granule cell bodies. When co-expressed in Xenopus oocytes with a Ca(V)2.1/beta(4) VDCC complex, either in the absence or presence of an alpha(2)delta(2) subunit, neither gamma(2) nor gamma(4) significantly modulated the VDCC peak current amplitude, voltage-dependence of activation or voltage-dependence of steady-state inactivation.Conclusion: The human gamma(2), gamma(3) and gamma(4) stargazin-like proteins are detected only in the CNS and display differential distributions among brain regions and several cell types in found in the cerebellum and hippocampus. These distribution patterns closely resemble those reported by other laboratories for the rodent orthologues of each protein. Whilst the fact that neither gamma(2) nor gamma(4) modulated the properties of a VDCC complex with which they could associate in vivo in Purkinje cells adds weight to the hypothesis that the principal role of these proteins is not as auxiliary subunits of VDCCs, it does not exclude the possibility that they play another role in VDCC function
channel amino terminus contributes determinants for β subunit‐mediated voltage‐dependent inactivation properties
No full text1Co-expression of auxiliary β subunits with the α1B Ca2+ channel subunit in COS-7 cells resulted in an increase in current density and a hyperpolarising shift in the mid-point of activation. Amongst the β subunits, β2a in particular, but also β4 and β1b caused a significant retardation of the voltage-dependent inactivation compared to currents with α1B alone, whilst no significant changes in inactivation properties were seen for the β3 subunit in this system.2Prevention of β2a palmitoylation, by introducing cysteine to serine mutations (β2a(C3,4S)), greatly reduced the ability of β2a to retard voltage-dependent inactivation.3Deletion of the proximal half of the α1B cytoplasmic amino terminus (α1BΔ1-55) differentially affected β subunit-mediated voltage-dependent inactivation properties. These effects were prominent with the β2a subunit and, to a lesser extent, with β1b. For β2a, the major effects of this deletion were a partial reversal of β2a-mediated retardation of inactivation and the introduction of a fast component of inactivation, not seen with full-length α1B. Deletion of the amino terminus had no other major effects on the measured biophysical properties of α1B when co-expressed with β subunits.4Transfer of the whole α1B amino terminus into α1C (α1bCCCC) conferred a similar retardation of inactivation on α1C when co-expressed with β2a to that seen in parental α1B.5Individual (α1B(Q47A) and α1B(R52A)) and double (α1B(R52,54A)) point mutations within the amino terminus of α1B also opposed the β2a-mediated retardation of α1B inactivation kinetics.6These results indicate that the α1B amino terminus contains determinants for β subunit-mediated voltage-dependent inactivation properties. Furthermore, effects were β subunit selective. As deletion of the α1B amino terminus only partially opposed β subunit-mediated changes in inactivation properties, the amino terminus is likely to contribute to a complex site necessary for complete β subunit function
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
Trafficking of N-type voltage-gated calcium ion channels and their regulation by alternative splicing
Full text linkN-type voltage-gated calcium (CaV2.2) channels are expressed predominantly in the central and peripheral nervous systems and play a crucial role in neurotransmitter release. Expression of these channels at the plasma membrane and in the membrane of presynaptic terminals is key for their function, however, how they are trafficked from the subcellular organelles is still poorly understood. In this study, trafficking of mutually-exclusive alternative splice variants of CaV2.2, containing either exon 37a or 37b at the proximal C-terminus and its mechanisms were examined. CaV2.2 with exon 37a (selectively expressed in nociceptors) reveals a significantly greater intracellular trafficking to the axons and plasma membrane of DRG neurons than CaV2.2 with exon 37b. Further examination of the amino acid sequence in exon 37 uncovers that the canonical binding motifs for adaptor protein 1 (AP-1), YxxΦ and [DE]xxxL[LI], present only in exon 37a are accountable for mediating the enhanced channel trafficking from the trans-Golgi network to the plasma membrane. Finally, the dopamine-2 receptor (D2R) and its agonist-induced activation, reveal differential effects on trafficking of these CaV2.2 isoforms. D2R slowed the endocytosis of CaV2.2 containing exon 37b but not exon 37a, and activation by the D2R-selective agonist quinpirole reversed the effect of the D2R. Disrupting the interaction between adaptor proteins and YxxΦ or [DE]xxxL[LI] in CaV2.2 perturbed these effects, suggesting that the interaction of adaptor proteins with CaV2.2 channels may also be key underlying mechanisms for differential trafficking of CaV2.2 splice variants, mediated by D2R. This study thus reveals key mechanisms involved in the trafficking of N-type calcium channels
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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