Browsing by Author "Coddou, Claudio"

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    Activation of Intra-nodose Ganglion P2X7 Receptors Elicit Increases in Neuronal Activity
    (2023) Alcayaga, Julio; Vera, Jorge; Reyna-Jeldes, Mauricio; Covarrubias, Alejandra A. A.; Coddou, Claudio; Diaz-Jara, Esteban; Del Rio, Rodrigo; Retamal, Mauricio A. A.
    Vagus nerve innervates several organs including the heart, stomach, and pancreas among others. Somas of sensory neurons that project through the vagal nerve are located in the nodose ganglion. The presence of purinergic receptors has been reported in neurons and satellite glial cells in several sensory ganglia. In the nodose ganglion, calcium depletion-induced increases in neuron activity can be partly reversed by P2X7 blockers applied directly into the ganglion. The later suggest a possible role of P2X7 receptors in the modulation of neuronal activity within this sensory ganglion. We aimed to characterize the response to P2X7 activation in nodose ganglion neurons under physiological conditions. Using an ex vivo preparation for electrophysiological recordings of the neural discharges of nodose ganglion neurons, we found that treatments with ATP induce transient neuronal activity increases. Also, we found a concentration-dependent increase in neural activity in response to Bz-ATP (ED50 = 0.62 mM, a selective P2X7 receptor agonist), with a clear desensitization pattern when applied every similar to 30 s. Electrophysiological recordings from isolated nodose ganglion neurons reveal no differences in the responses to Bz-ATP and ATP. Finally, we showed that the P2X7 receptor was expressed in the rat nodose ganglion, both in neurons and satellite glial cells. Additionally, a P2X7 receptor negative allosteric modulator decreased the duration of Bz-ATP-induced maximal responses without affecting their amplitude. Our results show the presence of functional P2X7 receptors under physiological conditions within the nodose ganglion of the rat, and suggest that ATP modulation of nodose ganglion activity may be in part mediated by the activation of P2X7 receptors.
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    Differential role of extracellular histidines in copper, zinc, magnesium and proton modulation of the P2X7 purinergic receptor
    (2007) Acuna-Castillo, Claudio; Coddou, Claudio; Bull, Paulina; Brito, Jocelyn; Huidobro-Toro, J. Pablo
    The P2X(7) receptor is a non-selective cationic channel activated by extracellular ATP, belonging to the P2X receptor family. To assess the role of extracellular histidines on the allosteric modulation of the rat P2X(7) receptor by divalent metals (copper, zinc and magnesium) and protons, these amino acid residues were singly substituted for corresponding alanines. Wild-type and mutated receptors were injected to Xenopus laevis oocytes; metal-related effects were evaluated by the two-electrode voltage-clamp technique. Copper inhibited the ATP-gated currents with a median inhibitory concentration of 4.4 +/- 1.0 mu mol/L. The inhibition was non-competitive and time-dependent; copper was 60-fold more potent than zinc. The mutant H267A, resulted in a copper resistant receptor; mutants H201A and H130A were less sensitive to copper inhibition (p < 0.05). The rest of the mutants examined, H62A, H85A, and H219A, conserved the copper-induced inhibition. Only mutants H267A and H219A were less sensitive to the modulator action of zinc. Moreover, the magnesium-induced inhibition was abolished exclusively on the H130A and H201A mutants, suggesting that this metal may act at a novel cationic modulator site. Media acidification inhibited the ATP-gated current 87 +/- 3%; out of the six mutants examined, only H130A was significantly less sensitive to the change in pH, suggesting that His-130 could be involved as a pH sensor. In conclusion, while His-267 is critically involved in the copper or zinc allosteric modulation, the magnesium inhibitory effects is related to His-130 and His-201, His-130 is involved in proton sensing, highlighting the role of defined extracellular histidines in rat P2X(7) receptor allosteric modulation.
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    Dissecting the facilitator and inhibitor allosteric metal sites of the P2X4 receptor channel -: Critical roles of Cys132 for zinc potentiation and Asp138 for copper inhibition
    (2007) Coddou, Claudio; Acuna-Castillo, Claudio; Bull, Paulina; Huidobro-Toro, J. Pablo
    Zinc and copper are atypical modulators of ligand-gated ionic channels in the central nervous system. We sought to identify the amino acids of the rat P2X(4) receptor involved in trace metal interaction, specifically in the immediate linear vicinity of His(140), a residue previously identified as being critical for copper-induced inhibition of the ATP-evoked currents. Site-directed mutagenesis replaced conspicuous amino acids located within the extracellular domain region between Thr(123) and Thr(146) for alanines. cDNAs for the wild-type and the receptor mutants were expressed in Xenopus laevis oocytes and examined by the two-electrode technique. Cys(132), but not Cys(126), proved crucial for zinc-induced potentiation of the receptor activity, but not for copper-induced inhibition. Zinc inhibited in a concentration-dependent manner the ATP-gated currents of the C132A mutant. Likewise, Asp(138), but not Asp(131) was critical for copper and zinc inhibition; moreover, mutant D138A was 20-fold more reactive to zinc potentiation than wild-type receptors. Asp(129), Asp131, and Thr(133) had minor roles in metal modulation. We conclude that this region of the P2X4 receptor has a pocket for trace metal coordination with two distinct and separate facilitator and inhibitor metal allosteric sites. In addition, Cys132 does not seem to participate exclusively as a structural receptor channel folding motif but plays a role as a ligand for zinc modulation highlighting the role of trace metals in neuronal excitability.
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    Prenatal to Early Postnatal Nicotine Exposure Impairs Central Chemoreception and Modifies Breathing Pattern in Mouse Neonates: A Probable Link to Sudden Infant Death Syndrome
    (SOC NEUROSCIENCE, 2008) Eugenin, Jaime; Otarola, Marcelo; Bravo, Eduardo; Coddou, Claudio; Cerpa, Veronica; Reyes Parada, Miguel; Llona, Isabel; von Bernhardi, Rommy
    Nicotine is a neuroteratogen and is the likely link between maternal cigarette smoking during pregnancy and sudden infant death syndrome (SIDS). Osmotic minipumps were implanted in 5-7 d CF1 pregnant mice to deliver nicotine bitartrate (60 mg Kg(-1) day(-1)) or saline (control) solutions for up to 28 d. Prenatal to early postnatal nicotine exposure did not modify the number of newborns per litter or their postnatal growth; however, nicotine-exposed neonates hypoventilated and had reduced responses to hypercarbia (inhalation of air enriched with 10% CO2 for 20 min) and hypoxia (inhalation of 100% N-2 for 20 s) at postnatal days 0-3 (P0-P3). In contrast, at postnatal day 8, nicotine-exposed neonates were indistinguishable from controls. Isolated brainstem-spinal cord preparations obtained from P0 to P3 nicotine-exposed neonates showed fictive respiration with respiratory cycles longer and more irregular than those of controls, as indicated by high short- and long-term variability in Poincare plots. In addition, their responses to acidification were reduced, indicating compromise of central chemoreception. Furthermore, the cholinergic contribution to central chemosensory responses switched from muscarinic receptor to nicotinic receptor-based mechanisms. No significant astrogliosis was detectable in the ventral respiratory group of neurons with glial fibrillary acidic protein immunohistochemistry. These results indicate that nicotine exposure affects the respiratory rhythm pattern generator and causes a decline in central chemoreception during early postnatal life. Consequently, breathing would become highly vulnerable, failing to respond to chemosensory demands. Such impairment could be related to the ventilatory abnormalities observed in SIDS.
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    Reactive Oxygen Species Potentiate the P2X(2) Receptor Activity through Intracellular Cys(430)
    (SOC NEUROSCIENCE, 2009) Coddou, Claudio; Codocedo, Juan F.; Li, Shuo; Lillo, Juan G.; Acuna Castillo, Claudio; Bull, Paulina; Stojilkovic, Stanko S.; Huidobro Toro, J. Pablo
    P2X receptor channels (P2XRs) are allosterically modulated by several compounds, mainly acting at the ectodomain of the receptor. Like copper, mercury, a metal that induces oxidative stress in cells, also stimulates the activity of P2X(2)R and inhibits the activity of P2X(4)R. However, the mercury modulation is not related to the extracellular residues critical for copper modulation. To identify the site(s) for mercury action, we generated two chimeras using the full size P2X(2) subunit, termed P2X(2a), and a splice variant lacking a 69 residue segment in the C terminal, termed P2X(2b), as the donors for intracellular and transmembrane segments and the P2X(4) subunit as the donor for ectodomain segment of chimeras. The potentiating effect of mercury on ATP-induced current was preserved in Xenopus oocytes expressing P2X(4/2a) chimera but was absent in oocytes expressing P2X(4/2b) chimera. Site-directed mutagenesis experiments revealed that the Cys(430) residue mediates effects of mercury on the P2X(2a)R activity. Because mercury could act as an oxidative stress inducer, we also tested whether hydrogen peroxide (H2O2) and mitochondrial stress inducers myxothiazol and rotenone mimicked mercury effects. These experiments, done in both oocytes and human embryonic kidney HEK293 cells, revealed that these compounds potentiated the ATP-evoked P2X(2a)R and P2X(4/2a)R currents but not P2X(2b)R and P2X(2a)-C430A and P2X(2a)-C430S mutant currents, whereas antioxidants dithiothreitrol and N-acetylcysteine prevented the H2O2 potentiation. Alkylation of Cys(430) residue with methylmethane-thiosulfonate also abolished the mercury and H2O2 potentiation. Altogether, these results are consistent with the hypothesis that the Cys(430) residue is an intracellular P2X(2a)R redox sensor.
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    The hypolipidemic drug metabolites nafenopin‐CoA and ciprofibroyl‐CoA are competitive P2Y1 receptor antagonists
    (2003) Coddou, Claudio; Bronfman A., Miguel L.; Huidobro-Toro, Juan Pablo
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    The release of sympathetic neurotransmitters is impaired in aged rats after an inflammatory stimulus: A possible link between cytokine production and sympathetic transmission
    (ELSEVIER IRELAND LTD, 2008) Donoso, Veronica; Gomez, Christian R.; Orriantia, Miguel Angel; Perez, Viviana; Torres, Claudio; Coddou, Claudio; Nelson, Pablo; Maisey, Kevin; Morales, Bernardo; Fernandez, Ricardo; Imarai, Monica; Huidobro Toro, Juan Pablo; Sierra, Felipe; Acuna Castillo, Claudio
    Aging results in a general decline in the response to external insults, including acute inflammatory challenges. In young animals, the inflammatory response requires activation of the sympathetic system, including neurotransmitters Such as ATP, and catecholamines (epinephrine and norepinephrine). To test whether aging affects activation of this axis, and whether this in turn might affect cytokine release, we administered lipopolysaccharide (LPS) i.p. to adult, middle-aged and aged Fisher 344 rats (6-, 15- and 23-month old, respectively) and evaluated the early (0-12 h) serum levels of Neuropeptide-Y (NP-Y), ATP and vanillyl mandelic acid (VMA, as in indirect measurement of catecholamine levels). In addition, we evaluated the association between these factors and serum levels of the cytokines tumor necrosis factor-alpha (TNF alpha) and interleukin-10 (IL-10). Induction of both ATP and NP-Y was markedly reduced in the serum of aged animals, when compared to their younger Counterparts, while induction of VMA was not affected by age. in spite of these changes, serum levels of TNF alpha and IL-10 were strongly hyper induced and delayed in aged rats. The results suggest that during aging there is a dys-regulation in sympathetic neurotransmitter regulatory Mechanisms, and this might play a role in the impairment of the inflammatory response. (C) 2008 Elsevier Ireland Ltd. All rights reserved.