Cross-inhibitory interactions between GABAA and P2X channels in myenteric neurones

Authors

  • Rustum Karanjia,

    1. Department of Anatomy & Cell Biology, Queen's University, Kingston, Ontario, Canada
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  • Luz M. García-Hernández,

    1. Instituto Potosino de Investigación Científica y Tecnológica (IPICYT), Camino a la Presa San José 2055, Col. Lomas 4a Sección, San Luis Potosí, SLP, CP78216, México
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  • Marcela Miranda-Morales,

    1. Instituto Potosino de Investigación Científica y Tecnológica (IPICYT), Camino a la Presa San José 2055, Col. Lomas 4a Sección, San Luis Potosí, SLP, CP78216, México
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  • Nureen Somani,

    1. Department of Anatomy & Cell Biology, Queen's University, Kingston, Ontario, Canada
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  • Rosa Espinosa-Luna,

    1. Department of Anatomy & Cell Biology, Queen's University, Kingston, Ontario, Canada
    2. Instituto Potosino de Investigación Científica y Tecnológica (IPICYT), Camino a la Presa San José 2055, Col. Lomas 4a Sección, San Luis Potosí, SLP, CP78216, México
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  • Luis M. Montaño,

    1. Departamento de Farmacología, Facultad de Medicina, UNAM, México D.F, México
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  • Carlos Barajas-López

    1. Department of Anatomy & Cell Biology, Queen's University, Kingston, Ontario, Canada
    2. Instituto Potosino de Investigación Científica y Tecnológica (IPICYT), Camino a la Presa San José 2055, Col. Lomas 4a Sección, San Luis Potosí, SLP, CP78216, México
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Dr Carlos Barajas-López, 2Instituto Potosino de Investigación Científica y Tecnológica, as above.
E-mail: cbarajas@ipicyt.edu.mx

Abstract

Inhibitory interactions between GABAA[induced by γ-aminobutyric acid (GABA)] and P2X [activated by adenosine 5′-triphosphate (ATP)] receptors of myenteric neurones from the guinea pig small intestine were characterized using whole-cell recordings. Currents induced by GABA (IGABA) or ATP (IATP) were inhibited by picrotoxin or pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid, respectively. Currents induced by GABA + ATP (IGABA+ATP) were only as large as the current induced by the most effective transmitter, revealing current occlusion. This occlusion requires maximal activation of at least one of these receptors. Sequential applications of neurotransmitters, and kinetic and pharmacological properties of IGABA+ATP indicate that they are carried through both GABAA and P2X channels. ATP did not affect IGABA in neurones: (i) in which P2X channels were not present; (ii) after inhibiting P2X channels with Ca2+ (iii) in the presence of pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid, a P2X receptor antagonist; (iv) after P2X receptor desensitization or (v) at IATP reversal potential. Similarly, GABA did not affect P2X-mediated currents in neurones: (i) in which GABAA channels were not present; (ii) in the presence of picrotoxin, a GABAA channel blocker; (iii) after GABAA receptor desensitization or (iv) at the IGABA reversal potential. Current occlusion occurred as fast as current activation and it was still present in the absence of Ca2+, at 11 °C, after adding to the pipette solution a cocktail of protein kinase inhibitors (staurosporine + genistein + K-252a), after substituting the GTP in the pipette with GDP-β-S and after treating the cells with N-ethylmaleimide. Taken together, all of these results are consistent with a model of cross-inhibition between GABAA and P2X.

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