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  • 1
    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
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  • 2
    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
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