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  • 1
    Electronic Resource
    Electronic Resource
    Effect of P2Y Agonists on Adenosine Transport in Cultured Chromaffin Cells (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 60 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Adenosine transport in cultured chromaffin cells was inhibited by purinergic P2y-receptor agonists without significant changes in the affinity constant, the values being between 1 ± 0.4 and 1.6 ± 0.6 μM. The Vmax parameter was modified significantly, being 40 ± 1.0, 26 ± 5.0, 32 ± 3.0, and 22 ± 4.7 pmol/106 cells/min for control, adenosine-5′-O-(2-thiodiphosphate), 5′-adenylylimidodiphosphate, and P1,P4-di(adenosine-5′-) tetraphosphate (Ap4A) (100 μM for every effector), respectively. Ap4A, a physiological ligand for P2y receptors in chromaffin cells, showed the highest inhibitory effect (45%). This transport inhibition is explained by an increase in the cytosolic Ca2+ concentration ([Ca2+]i) and the activation of protein kinase C (PKC). Experiments of [Ca2+]i measurement with the fura-2 technique showed that P2y agonists, as well as bradykinin, were able to increase [Ca2+]i, this effect being independent of the presence of extracellular Ca2+. The peptide bradykinin, determined to be coupled to phosphatidylinositol hydrolysis and internal Ca2+ mobilization in chromaffin cells, exhibited a behavior similar to that of P2y agonists in adenosine transport inhibition (39%). P2y agonists and bradykinin increased PKC activity associated with the membrane fraction (about 50% increase in particulate PKC activity with respect to controls). The present studies suggest that adenosine transport is regulated by P2y-purinergic receptors mediated via Ca2+ mobilization and PKC activation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb03192.x
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  • 2
    Electronic Resource
    Electronic Resource
    Nerve Growth Factor Effect on Adenosine Transport in Cultured Chromaffin Cells (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: Chromaffin cells both recently isolated or in culture present a high-affinity adenosine transporter with a Km value of 1 μM. When cells were exposed to nerve growth factor (NGF; 10 ng/ml), the adenosine transporter affinity decreased to 3μM. This value was maintained from 3 days after plating to the end of the culture period. A change in the transport capacity was observed, with a significant increase (˜200–260%) in NGF-cultured cells throughout the period studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1987.tb13152.x
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  • 3
    Electronic Resource
    Electronic Resource
    Dopamine Receptor Blockade Inhibits the Amphetamine-Induced Release of Diadenosine Polyphosphates, Diadenosine Tetraphosphate and Diadenosine Pentaphosphate, from Neostriatum of the Conscious Rat (1995)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 64 (1995), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The diadenosine polyphosphates diadenosine tetraphosphate (Ap4A) and diadenosine pentaphosphate (Ap5A) are costored with ATP and released in a calcium-dependent manner from neural preparations in vitro. By means of a push-pull perfusion system, samples from conscious rat were collected from the caudate putamen area, and nucleotide compounds were analyzed by HPLC. The adenine dinucleotides were not detectable before systemic amphetamine injection. The maximal levels were reached 20 min after injection, independently of the dose. The EC50 values for amphetamine-induced release of dinucleotides were 2.04 ± 0.15 and 2.43 ± 0.36 mg/kg for Ap4A and Ap5A, respectively. Amphetamine doses higher than 5 mg/kg did not increase the dinucleotide release, the maximal values being 12.9 ± 0.9 and 11.5 ± 0.9 pmol/fraction for Ap4A and Ap5A, respectively, which corresponds with 64.5 and 57.5 nM in the samples. Adenosine and AMP were present in push-pull samples from rat brain under basal conditions. Their levels were 15 pmol/fraction (75 nM) and 50 pmol/fraction (250 nM) for adenosine and AMP, respectively. A significant increase was obtained for both compounds after amphetamine injection. The adenosine increase reached 45 pmol/sample (225 nM), which was 200% of the basal value 20 min after the stimulant administration. The increase at other times was not significant. The AMP levels increased significantly from 10 to 50 min. The maximal level was reached 20 min after amphetamine injection, with 150 pmol/fraction (750 nM), which represents a 200% increase with respect to the basal level. The adenine dinucleotide release was blocked by the dopamine receptor antagonist haloperidol, which returned the levels to the control basal values. It is suggested that dopamine, released in a nonexocytotic way by the action of amphetamine, induces the release of the dinucleotides Ap4A and Ap5A in the neostriatum area through dopaminergic receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1995.64020670.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of 5′-(N-Ethylcarboxamido)adenosine on Adenosine Transport in Cultured Chromaffin Cells (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: Abstract: Extracellular adenosine is transported into chromaffin cells by a high-affinity transport system. The action of adenosine receptor ligands was studied in this cellular model 5-(N-Ethylcarboxamido)adenosine (NECA), an agonist receptors, activated adenosine transport. Km values for adenosine were 4.6 ± 1.0 (n = 5) and 10.2 ± 3.0 μM (n = 5) for controls and 100 nM NECA, respectively. The Vmax values were 66.7 ± 23.5 and 170.2 ± 30 pmol/106 cells/min for control and 100 nM NECA, respectively. The A1 agonist N6-cyclohexyladenosine, the A1 antagonist 8-cyclopentyl-1, 3-dipropylxanthine, and the A1-A2 antagonist 1,3-dipropyl-8-{4-[(2-aminoethyl)amino]-carbonylmethyloxyphenyl}-xanthine did not significantly modify the adenosine transport in this system. Binding studies done with [3H]dipyridamole, a nucleoside transporter ligand, did not show changes in either the number or affinity of transporter sites after NECA treatment. This ligand can enter cells and quantifies the total number of transporters. The binding studies with [3H]-nitrobenzylthioinosine, which quantifies the plasma membrane transporters, showed a Bmax of 19,200 ± 800 and 23,200 ± 700 transporters/cell for controls and 100 nM NECA, repectively. No changes in the KD were obtained. The effects of NECA were not mediated through adenylate cyclase activation, because its action was not imitated by forskolin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1990.tb04895.x
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  • 5
    Electronic Resource
    Electronic Resource
    Nitric Oxide-Sensitive Guanylyl Cyclase Activity Inhibition Through Cyclic GMP-Dependent Dephosphorylation (2000)
    Oxford UK : Blackwell Science Ltd.
    Journal of neurochemistry 75 (2000), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The soluble form of guanylyl cyclase (sGC) plays a pivotal role in the transduction of inter- and intracellular signals conveyed by nitric oxide. Here, a feedback inhibitory mechanism triggered by cyclic guanosine-3′,5′-monophosphate (cGMP)-dependent protein kinase (PKG) activation is described. Preincubation of chromaffin cells with C-type natriuretic peptide, which increased cGMP levels and activated PKG, or with cGMP-permeant analogue (which also activates PKG), in the presence of a broad-spectrum phosphodiesterase inhibitor, resulted in a decrease in subsequent sodium nitroprusside (SNP)-dependent cGMP elevations. This inhibitory effect was mimicked by activating a protein phosphatase and counteracted by the selective PKG inhibitor KT-5823 and by different protein phosphatase inhibitors. Immunoprecipitation of sGC from cells submitted to different treatments followed by immunodetection with antiphosphoserine antibodies (clone 4A9) showed changes in phosphorylation levels of the β subunit of sGC, and these changes correlated well with differences in SNP-elicited cGMP accumulations. Pretreatment of cells with several PKG inhibitors or protein phosphatase inhibitors produced an enhancement of SNP-stimulated cGMP rises without changing the SNP concentration required to produce half-maximal or maximal responses. Taken together, these results indicate that the catalytic activity of sGC is closely coupled to the phosphorylation state of its β subunit and that the tonic activity of PKG or its stimulation regulates sGC activity through dephosphorylation of the β subunit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2000.0752029.x
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  • 6
    Electronic Resource
    Electronic Resource
    Coexpression of Several Types of Metabotropic Nucleotide Receptors in Single Cerebellar Astrocytes (2000)
    Oxford UK : Blackwell Science Ltd.
    Journal of neurochemistry 75 (2000), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We have examined the expression of mRNA for several P2Y nucleotide receptors by northern blot analysis in purified type 1 cerebellar astrocyte cultures. These results suggest that different P2Y subtypes could be responsible for ATP metabotropic calcium responses in single type 1 astrocytes. To identify these subtypes we have studied the pharmacological profile of ATP calcium responses using fura-2 microfluorimetry. All tested astrocytes responded to ATP and UTP stimulations evoking similar calcium transients. Most astrocytes also responded to 2-methylthioATP and ADP challenges. The agonist potency order was 2-methylthioATP 〉 ADP 〉 ATP = UTP. Cross-desensitization experiments carried out with ATP, UTP, and 2-methylthioATP showed that 2-methylthioATP and UTP interact with different receptors, P2Y1 and P2Y2 or P2Y4. In a subpopulation of type 1 astrocytes, ATP prestimulation did not block UTP responses, and UDP elicited clear intracellular Ca2+ concentration responses at very low concentrations. 2-MethylthioATP and UTP calcium responses exhibited different sensitivity to pertussis toxin and different inhibition patterns in response to P2 antagonists. The P2Y1-specific antagonist N6-methyl-2′-deoxyadenosine 3′,5′-bisphosphate (MRS 2179) specifically blocked the 2-methylthio-ATP responses. We can conclude that all single astrocytes coexpressed at least two types of P2Y metabotropic receptors: P2Y1 and either P2Y2 or P2Y4 receptors. Moreover, 30-40% of astrocytes also coexpressed specific pyrimidine receptors of the P2Y6 subtype, highly selective for UDP coupled to pertussis-toxin insensitive G protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2000.0752071.x
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  • 7
    Electronic Resource
    Electronic Resource
    Dinucleotide Receptor Modulation by Protein Kinases (Protein Kinases A and C) and Protein Phosphatases in Rat Brain Synaptic Terminals (1997)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 68 (1997), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The diadenosine polyphosphates, diadenosine tetraphosphate and diadenosine pentaphosphate (Ap5A), can activate an ionotropic dinucleotide receptor that induces Ca2+ transients into synaptosomes prepared from rat brain. This receptor, also termed the P4 purinoceptor, is sensitive only to adenine dinucleotides and is insensitive to ATP. Studies on the modulatory role of protein kinase A (PKA), protein kinase C (PKC), and protein phosphatases on the response of diadenosine polyphosphate receptors were performed by measuring the changes in the intracellular Ca2+ levels with fura-2. Activation and inhibition of PKA were carried out by means of forskolin and the PKA inhibitory peptide (PKA-IP), respectively. The Ap5A response was inhibited by forksolin to 35% of control values, but PKA-IP induced an increase of 37%. The effect of PKC activation was similar to that observed for PKA. PKC stimulation with phorbol 12,13-dibutyrate produced an inhibition of 67%, whereas the PKC inhibitors staurosporine and PKC inhibitory peptide enhanced the responses elicited by Ap5A to 40% in both cases. Protein phosphatase inhibitors diminished the responses elicited by Ap5A to 17% in the case of okadaic acid, to 50% for microcystin, and to 45% in the case of cyclosporin A. Thus, the activity of dinucleotide receptors in rat brain synaptosomes appears to be modulated by phosphorylation/dephosphorylation. These processes could be of physiological significance in the control of transmitter release from neurons that are postsynaptic to nerves that release diadenosine polyphosphates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1997.68062552.x
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  • 8
    Electronic Resource
    Electronic Resource
    Specific diadenosine pentaphosphate receptor coupled to extracellular regulated kinases in cerebellar astrocytes (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: In this study, we show specific intracellular responses evoked by the stimulation of astrocytes with the P1,P5-di(adenosine-5′)pentaphosphate, Ap5A. The stimulation of astrocytes with micromolar concentrations of the dinucleotide elicited rapid increases in intracellular calcium concentration ([Ca2+]i), showing an EC50 value of 15.27 ± 0.61 µm. Moreover, the stimulation of cells with nanomolar concentrations of Ap5A, unable to induce calcium responses, increased the phosphorylated forms of extracellular-signal regulated kinase 1/2 (ERK) with an EC50 value of 9.8 ± 2.4 nm. The maximal activation was observed at 100 nm Ap5A, which was similar to that produced by epidermal growth factor (EGF) under the same experimental conditions. The present data reported here indicate that Ap5A mediated these effects by interacting with a specific receptor, not yet identified, which was different from the P2Y1 and P2Y2/P2Y4 receptors present in all individual astrocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2002.01111.x
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  • 9
    Electronic Resource
    Electronic Resource
    Single GABAergic synaptic terminals from rat midbrain exhibit functional P2X and dinucleotide receptors, able to induce GABA secretion (2001)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 77 (2001), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: GABAergic terminals from rat midbrain characterized by immunolocalization of glutamic acid decarboxylase and/or the vesicular inhibitory amino acid transporter respond to ATP or P1,P5-di(adenosine-5′) pentaphosphate (Ap5A) with an increase in the intrasynaptosomal calcium concentration measured by a microfluorimetric technique in single synaptic terminals. The ATP response is mediated through the activation of P2X receptors with an abundant presence of P2X3 subunits. Ap5A, however, exerts its effects by acting through a different receptor termed the dinucleotide receptor. Both receptors, once activated in the presence of extrasynaptosomal calcium, induce a concentration-dependent GABA release from synaptosomal populations with EC50 values of 16 and 20 µm for ATP and Ap5A, respectively. Specific inhibition of GABA release is obtained with pyridoxal phosphate-6-azophenyl-2′,4′-disulphonic acid (80 µm) on the ATP effect and with P1,P5-di(inosine-5′) pentaphosphate (100 nm) on the dinucleotide receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2001.00228.x
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  • 10
    Electronic Resource
    Electronic Resource
    Glycogen Metabolism in Bovine Adrenal Medulla (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 38 (1982), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Glycogen content was determined both in whole adrenal medullary tissue and in isolated adrenal chromaffin cells, in which it responds to glucose deprivation and restoration. [14C]glucose incorporation into glycogen in isolated adrenal chromaffin cells is increased by previous glucose deprivation (“fasting”). Total glycogen synthase activities are 452 ± 66 mU/g in whole tissue and 305 ± 108 mU/g in isolated cells. The Km of glycogen synthase for UDP-glucose is 0.67 mM with 13 mm glucose-6-phosphate and 1 mm without this effector. The in vitro inactivation process of glycogen synthase a has been found to be mainly cyclic AMP-dependent, but it also responds to Ca2+. Total glycogen phosphorylase activities are 8.69 ± 1.26 U/g in whole tissue and 2.38 ± 0.30 U/g in isolated cells. The requirements for interconversion in vitro of both glycogen synthase and phosphorylase suggest a system similar to that of other tissues. During incubation of isolated adrenal chromaffin cells with 5 mm-glucose, phosphorylase a activity decreases and synthase a activity increases; these changes are more marked in “fasted” cells. Glycogen content and glycogen synthase and phosphorylase activities are higher in the adrenal medulla than in the brain, suggesting a greater metabolic role of glycogen in the adrenal medulla.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1982.tb08652.x
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