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  • 1
    Electronic Resource
    Electronic Resource
    Presence of functional ATP and dinucleotide receptors in glutamatergic synaptic terminals from rat midbrain (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 87 (2003), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Glutamatergic terminals from rat midbrain were characterized by immunolocalization of synaptophysin and the vesicular glutamate transporters, either VGLUT1 or VGLUT2. Terminals containing these markers represent about 31% (VGLUT1) and 16% (VGLUT2) of the total synaptosomal population. VGLUT1-positive glutamatergic terminals responded to ATP or P1,P 5-di(adenosine-5′) pentaphosphate (Ap5A) with an increase in the intrasynaptosomal calcium concentration as measured by a microfluorimetric technique in single synaptosomes. Roughly 20% of the VGLUT1-positive terminals responded to ATP, 13% to Ap5A and 11% to both agonists. Finally 56% of the terminals labeled with the anti-VGLUT1 antibody did not show any calcium increase in response to ATP or Ap5A. A similar response distribution was also observed in the VGLUT2-positive terminals. The Ca2+ responses induced by ATP and Ap5A in the glutamatergic terminals could be selectively inhibited by pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS, 80 µm) and P1,P 5-di(inosine-5′) pentaphosphate (Ip5I, 100 nm), respectively. Both ATP and Ap5A, once assayed in the presence of extrasynaptosomal calcium, were able to induce a concentration-dependent glutamate release from synaptosomal populations, EC50 values being 21 µm and 38 µm for ATP and Ap5A, respectively. Specific inhibition of glutamate release was obtained with PPADS on the ATP effect and with Ip5I on the dinucleotide response, indicating that separate receptors mediate the secretory effects of both compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2003.01975.x
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of Nucleotide Transport into Rat Brain Synaptic Vesicles (1999)
    Oxford UK : Blackwell Science Ltd
    Journal of neurochemistry 73 (1999), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract : ATP transport to synaptic vesicles from rat brain has been studied using the fluorescent substrate analogue 1,N6-ethenoadenosine 5′-triphosphate (ε-ATP), The increase in intravesicular concentration was time dependent for the first 30 min, ε-ATP being the most abundant nucleotide. The complexity of the saturation curve indicates the existence of kinetic and allosteric cooperativity in the nucleotide transport, which exhibits various affinity states with K0.5 values of 0.39 ± 0.06 and 3.8 ± 0.1 mM with ε-ATP as substrate. The Vmax values obtained were 13.5 ± 1.4 pmol · min-1· mg of protein-1 for the first curve and 28.3 ± 1.6 pmol · min-1· mg of protein-1 considering both components. This kinetic behavior can be explained on the basis of a mnemonic model. The nonhydrolyzable adenine nucleotide analogues adenosine 5′-O-3-(thiotriphosphate), adenosine 5′-(β,γ-imino)triphosphate and the diadenosine polyphosphates P1,P3-di(adenosine)triphosphate, P1,P4-di(adenosine)tetraphosphate, and P1,P5-di(adenosine)pentaphosphae the nucleotide transport. The mitochondrial ATP/ADP exchange inhibitor atractyloside, N-ethylmaleimide, and polysulfonic aromatic compounds such as Evans blue and 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid also inhibit ε-ATP vesicular transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1999.0731098.x
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  • 4
    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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