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  • 1
    Electronic Resource
    Electronic Resource
    Coupling of Astroglial α2-Adrenoreceptors to Second Messenger Pathways (1996)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 66 (1996), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We have investigated which α2-receptor subtypes are expressed in cultured cortical astroglia, and their coupling to second messengers. Binding assays using [3H]rauwolscine showed a very low number of α2 receptors in the astrocytic cultures. Treatment of cultures with dibutyryl cyclic AMP (dBcAMP) increased significantly the number of receptors. The RNase protection assay was used to investigate which receptor subtype the cells express. The α2B message was expressed at a low level in both treated and untreated cells, the levels of mRNA for the α2A/D subtype were up-regulated significantly in cells treated with dBcAMP and no expression of mRNA for the α2C subtype was detected. The α2 agonist dexmedetomidine inhibited forskolin-induced increases in cyclic AMP both in treated and untreated cultures in a pertussis toxin-dependent manner. This effect was abolished by the α2-receptor antagonist rauwolscine. Selective α2-receptor agonists dexmedetomidine, clonidine, and UK14,304 all increased intracellular calcium only in dBcAMP-treated cells. The antagonist rauwolscine abolished this effect. Ca2+ responses were also seen in the absence of extracellular Ca2+ and they were inhibited by the phospholipase C inhibitor U-73122, suggesting that astroglial α2 receptors are coupled to the inositol phospholipid pathway. We therefore also tested the effect of dexmedetomidine directly on inositol 1,4,5-trisphosphate accumulation. A significant increase was seen that was blocked by the antagonist rauwolscine and, as expected, by U-73122. In short, the results demonstrate that the α2 receptors in astroglia are coupled to multiple second messenger pathways. They are up-regulated in cells treated with dBcAMP, which simultaneously assume a process-bearing morphology. If this morphological change reflects some in vivo process such as reactive gliosis, the up-regulation of α2-receptor expression could mean an adaptive change in astrocytic responses to a common neurotransmitter, noradrenaline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1996.66062394.x
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  • 2
    Electronic Resource
    Electronic Resource
    Interactions of Glutamate Receptor Agonists Coupled to Changes in Intracellular Ca2+ in Rat Cerebellar Granule Cells in Primary Culture (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 57 (1991), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: : Changes in cytosolic free Ca2+ concentrations in response to glutamate receptor agonists and their interactions were studied in rat cerebellar granule cells grown on cover-slips. The intracellular Ca2+ as measured with fura-2 increased by applying kainate (KA), quisqualate (QU), and N-methyl-d-aspartate (NMDA). The effect of KA could not be blocked by the NMDA receptor blocker 2-amino-5-phosphonovalenc acid (APS). The KA-and QU-induced increase in intracellular free Ca2+ was also observed in a Na+-free medium, indicating that this response is not secondarily due to the depolarization. The effect of 10 μM QU on the KA-induced changes in cytosolic free Ca2+ was additive only at low KA concentrations, but QU at 0.1 mM totally blocked the response to KA. In the presence of 10 μM KA, the dose-response curve of QU became biphasic, whereas with 50 μM KA, a reduction of the response was seen around 1–100 μM QU. The effect of NMDA on the QU-induced response was additive only at low QU concentrations. It is proposed that rat cerebellar granule cells in primary culture express separate receptor-channel complexes for NMDA, QU, and KA, but interactions between agonists for these receptor sites exist. Thus, QU when present at intermediate concentrations seems to interact with the KA type of receptor, causing its desensitization. At high QU concentrations, an interaction of QU with the NMDA receptor site is apparent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1991.tb06374.x
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  • 3
    Electronic Resource
    Electronic Resource
    Ionic Dependence of Membrane Potential and Glutamate Receptor-Linked Responses in Synaptoneurosomes as Measured with a Cyanine Dye, DiS-C2-(5) (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 48 (1987), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Membrane potentials of particles present in a sub-cellular brain preparation, called synaptoneurosomes, have been monitored by measurement of changes in the absor-bance of a cyanine dye, DiS-C2-5. The membrane potential of the particles seems to be dependent on both Cl− and K+ diffusion potentials, as judged from dependence of the ab-sorbance changes on the K+ equilibrium potential across the membrane in the presence of Ba2+ or when Cl− was replaced with gluconate. The apparent high Cl− permeability of the membrane preparation was reduced in the presence of pic-rotoxin, a finding suggesting endogenous activation of receptor-linked Cl− channels. Glutamate and kainate caused depolarization of the membranes present in the preparation. This effect was only seen if K+ channels had been blocked in the presence of Ba2+ or 4-aminopyridine. No responses were observed with other glutamate receptor agonists (quisqualate or N-methyl-d-aspartate). The membrane potential of particles present in conventional synaptosomal preparations neither had a high Cl− permeability nor reacted to glutamate or kainate in the present conditions. The results suggest that synaptoneurosome preparations may be used for functional studies on postsynaptic neurotransmit-ter receptor-linked membrane potential changes with optical probes of membrane potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1987.tb04128.x
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  • 4
    Electronic Resource
    Electronic Resource
    12-O-Tetradecanoylphorbol 13-Acetate and Forskolin Modify Muscarinic Receptor-Linked Ca2+ Mobilization in SH-SY5Y Neuroblastoma Cells Through Different Mechanisms (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 54 (1990), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA), which causes differentiation of SH-SY5Y neuroblastoma cells, reduces carbachol binding and carbachol-stimulated Ca2+ mobilization in these cells. The decrease in responsiveness to carbachol is due partially to a reduction in the amount of Ca2+ released by the cells and partially to a decrease in the sensitivity of the cells to carbachol. These effects probably can be attributed to a reduction in muscarinic receptor number and a decrease in receptor affinity, respectively. Forskolin, an alkaloid known to cause an increase in cellular cyclic AMP, enhances Ca2+ influx into the cells without affecting the cytosolic free Ca2+ concentration. The alkaloid causes an apparent restoration of the reduced Ca2+ release, caused by TPA, but does not affect the sensitivity of the cells to carbachol. Forskolin increases the decay of carbachol-induced increase in cytosolic Ca2+. The effects of TPA appear to be linked directly to receptor function, whereas those of forskolin are due to the effect of cyclic AMP on cellular Ca2+ metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1990.tb01899.x
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  • 5
    Electronic Resource
    Electronic Resource
    Ethanol Specifically Inhibits NMDA Receptors with Affinity for Ifenprodil in the Low Micromolar Range in Cultured Cerebellar Granule Cells (1997)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 69 (1997), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The effect of ethanol on the intracellular Ca2+ concentration response to NMDA in rat cerebellar granule cells grown in low or high KCI concentrations has been studied using image analysis. The cells grown in low KCI displayed high sensitivity for glycine. The subtype-selective antagonist ifenprodil inhibited the response with high (in the low micromolar range) and low (in the high micromolar range) potency. Ethanol affected the high-potency component in these cultures. In cells grown in high KCI the glycine sensitivity was lower, and a low potency for ifenprodil (high micromolar) dominated. These cells were not significantly sensitive to ethanol. The results indicate that the component displaying potency for ifenprodil in the low micromolar range with properties of the NR2B subunit is the target for ethanol action on the NMDA receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1997.69052162.x
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  • 6
    Electronic Resource
    Electronic Resource
    Prevention of NMDA-induced death of cortical neurons by inhibition of protein kinase Cζ (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 86 (2003), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Excitotoxicity through stimulation of N-methyl-d-aspartate (NMDA) receptors contributes to neuronal death in brain injuries, including stroke. Several lines of evidence suggest a role for protein kinase C (PKC) isoforms in NMDA excitotoxicity. We have used specific peptide inhibitors of classical PKCs (α, β, and γ), novel PKCs δ and ε, and an atypical PKCζ in order to delineate which subspecies are involved in NMDA-induced cell death. Neuronal cell cultures were prepared from 15-day-old mouse embryos and plated onto the astrocytic monolayer. After 2 weeks in vitro the neurons were exposed to 100 µm NMDA for 5 min, and 24 h later the cell viability was examined by measuring the lactate dehydrogenase release and bis-benzimide staining. While inhibitors directed to classical (α, β, and γ) or novel PKCs (δ or ε) had no effect, the PKCζ inhibitor completely prevented the NMDA-induced necrotic neuronal death. Confocal microscopy confirmed that NMDA induced PKCζ translocation, which was blocked by the PKCζ inhibitor. The NMDA-induced changes in intracellular free Ca2+ were not affected by the peptides. In situ hybridization experiments demonstrated that PKCζ mRNA is induced in the cortex after focal brain ischemia. Altogether, the results indicate that PKCζ activation is a downstream signal in NMDA-induced death of cortical neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2003.01846.x
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  • 7
    Electronic Resource
    Electronic Resource
    Calcium and plant organelles (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 7 (1984), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The role of intracellular organelles in the regulation of cytosolic Ca2+ levels and whether changes in these levels affect organelle metabolism is considered. We have assessed the biochemical properties of the Ca2+ transporting systems in mitochondrial, chloroplast and microsomal fractions. It is proposed that although all of these organelles can transport Ca2+ to varying extents it would appear that in some tissues at least mitochondria do not play a significant role in the maintenance of cytosolic Ca2+. The most important Ca2+ transporting systems are probably the ATP dependent Ca2+ extrusion across the plasma membrane and Ca2+ uptake by endoplasmic reticulum, as well as light driven Ca2+ uptake by chloroplasts. Changes in cytoplasmic [Ca2+] do appear to regulate the activity of NAD kinase in chloroplasts, the mitochondrial external NADH dehydrogenase and intra-mitochondrial glutamate dehydrogenase, all of which play a key role in plant cell metabolism. Since some of these enzymes are affected by primary stimuli such as light or hormones, it is concluded that Ca2+ may act as a second messenger mediating some of the primary responses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1984.tb01432.x
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  • 8
    Electronic Resource
    Electronic Resource
    Locatization of Voltaae-sensitive Ca2+ Fluxes and Neuropeptide Y Immunoreactivity to Varicosities in SH-SY5Y Human Neuroblastoma Cells Differentiated by Treatment with the Protein Kinase Inhibitor Staurosporine (1997)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 9 (1997), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The distribution of voltage-sensitive elevations of the level of Ca2+ in untreated SH-SY5Y cells and cells that had been induced to differentiate with staurosporine was investigated by monitoring fura-2 fluorescence in cell suspensions, and by using microfluorometry and quantitative fluorescence imaging on cell bodies and on cellular processes. Cell bodies of both types of cells displayed small Ca2+ elevations, which were composed of transient and sustained components. Elevations were partially sensitive to the L- and N-channel blockers nifedipine (1 μM) and ω-conotoxin GVIA (100 nM) respectively. Up to ten times higher Ca2+ elevations were observed in varicosities of treated cells than in cell bodies of treated and untreated cells. These elevations were insensitive to compounds known to release Ca2+ from intracellular stores. Elevations of Ca2+ were sustained, and they were insensitive to 5 pM nifedipine, 100 nM ω-agatoxin IVA and 100 nM ω-conotoxin GVIA, and partially sensitive to 2 pM ω-conotoxin GVIA, indicating predominance of non-L-type, non-N-type, non-P-type channel activity. The intracellular localization of neuropeptide Y, a marker of differentiation in these cells, was also investigated by fluorescence immunocytochemistry. Varicosities of treated cells displayed marked fluorescence when viewed in a confocal microscope. These findings show that the varicosities of staurosporine-treated cells exhibit some of the functional properties of nerve terminals. The varicosities resemble boutons en passant nerve endings and they seem to express Ca2+ channels different from those in the cell body.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1997.tb01362.x
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  • 9
    Electronic Resource
    Electronic Resource
    Different roles for Gi and Go proteins in modulation of adenylyl cyclase type-2 activity (2002)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 83 (2002), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The effect of Gi/o protein-coupled receptors on adenylyl cyclase type 2 (AC2) has been studied in Sf9 insect cells. Stimulation of cells expressing AC2 with the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) led to a twofold stimulation of cAMP synthesis that could be blocked with the protein kinase C inhibitor GF109203X. Activation of a coexpressed α2A-adrenoceptor or muscarinic M4 receptor inhibited the stimulation by TPA almost completely in a pertussis toxin-sensitive manner. Activation of Gs proteins switched the response of the α2A-adrenoceptor to potentiation of prestimulated AC2 activity. The potentiation, but not the inhibition, could be blocked by a Gβγ scavenger. A novel methodological approach, whereby signalling through endogenous G proteins was ablated, was used to assess specific G protein species in the signal pathway. Expression of Go proteins (αo1 + β1γ2) restored both the inhibition and the potentiation, whereas expression of Gi proteins (αi1 + β1γ2) resulted in a potentiation of both the TPA- and the Gs-stimulated AC2 activity. The data presented supports the view of AC2 as a molecular switch and implicates this isoform as a target for Go protein-linked signalling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2002.01270.x
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  • 10
    Electronic Resource
    Electronic Resource
    A phorbol ester induces secretion of alkaline phosphatase activity in human osteosarcoma cells (1992)
    Springer
    Calcified tissue international 50 (1992), S. 533-540 
    Details
    ISSN: 1432-0827
    Keywords: Osteosarcoma cells ; Alkaline phosphatase activity ; Phorbol ester-U-2 OS cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The phorbol ester 12-O-tetradecanoyl-13-acetate (TPA) blocked the growth of, and induced the appearance of processes in the human osteosarcoma cell line U-2 OS. The phorbol ester decreased the intracellular level of alkaline phosphatase (APase) activity (as measured per mg cell protein) and caused a marked increase in the APase activity secreted from the cells into the culture medium. The secretion of APase appeared after a lag period of 4–6 hours of TPA treatment, and it could also be visualized with histological staining. Differential ultracentrifugation of the culture media showed that the APase was released to the media in the form of vesicles. The vesicles were studied by electron microscopy and appeared similar to matrix vesicles isolated from cartilage and chondrocytes. It is thus concluded that TPA is able to induce the primary steps of mineralization in these cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582169
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