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Research ArticleNEUROPHARMACOLOGY

Pentylenetetrazole-Induced Inhibition of Recombinant γ-Aminobutyric Acid Type A (GABAA) Receptors: Mechanism and Site of Action

Ren-Qi Huang, Cathy L. Bell-Horner, Mohammed I. Dibas, Douglas F. Covey, John A. Drewe and Glenn H. Dillon
Journal of Pharmacology and Experimental Therapeutics September 2001, 298 (3) 986-995;
Ren-Qi Huang
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Cathy L. Bell-Horner
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Mohammed I. Dibas
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Douglas F. Covey
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John A. Drewe
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Glenn H. Dillon
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Abstract

Pentylenetetrazole (PTZ) is a central nervous system convulsant that is thought, based on binding studies, to act at the picrotoxin (PTX) site of the γ-aminobutyric acid type A (GABAA) receptor. In the present study, we have investigated the mechanism and site of action of PTZ in recombinant GABAA receptors. In rat α1β2γ2 receptors, PTZ inhibited GABA-activated Cl− current in a concentration-dependent, voltage-independent manner, with an IC50 of 0.62 ± 0.13 mM. The mechanism of inhibition appeared competitive with respect to GABA in both rat and human α1β2γ2 receptors. Varying subunit configuration (change or lack of α subunit isoform or lack of γ2 subunit) had modest effects on PTZ-induced inhibition, as evidenced by comparable IC50values (0.6–2.2 mM) in all receptor configurations tested. This contrasts with PTX and other PTX-site ligands, which have greater affinity in receptors lacking an α subunit. Using a one-site model for PTZ interaction with α1β2γ2 receptors, the association rate (k+1) was found to be 1.14 × 103 M−1 s−1 and the dissociation rate (k−1) was 0.476 s−1, producing a functional kd of 0.418 mM. PTZ could only gain access to its binding site extracellularly. Single-channel recordings demonstrated that PTZ decreased open probability by increasing the duration of closed states but had no effect on single-channel conductance or open state duration. α-Isopropyl-α-methyl-γ-butyrolactone, a compound known to antagonize effects of PTX, also diminished the effects of PTZ. Taken together, our results indicate that pentylenetetrazole and picrotoxin interact with overlapping but distinct domains of the GABAAreceptor.

Footnotes

  • This work was supported by National Institutes of Health Grants ES07904 (to G.H.D.), NS14834 (to D.F.C.), and Texas Advanced Research Program Grant 009768-027 (to G.H.D.).

  • Abbreviations:
    GABA
    γ-aminobutyric acid
    αIMGBL
    α-isopropyl-α-methyl-γ-butyrolactone
    HEK
    human embryonic kidney
    PTX
    picrotoxin
    PTZ
    pentylenetetrazole
    ANOVA
    analysis of variance
    TM
    transmembrane domain
    TBPS
    t-butylbicyclophosporothionate
    U-93631
    4-dimethyl-3-t-butylcarboxyl-4,5-dihydro(1,5-a)quinoxaline
    Po
    open channel probability
    • Received March 1, 2001.
    • Accepted May 15, 2001.
  • The American Society for Pharmacology and Experimental Therapeutics
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Journal of Pharmacology and Experimental Therapeutics: 298 (3)
Journal of Pharmacology and Experimental Therapeutics
Vol. 298, Issue 3
1 Sep 2001
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Research ArticleNEUROPHARMACOLOGY

Pentylenetetrazole-Induced Inhibition of Recombinant γ-Aminobutyric Acid Type A (GABAA) Receptors: Mechanism and Site of Action

Ren-Qi Huang, Cathy L. Bell-Horner, Mohammed I. Dibas, Douglas F. Covey, John A. Drewe and Glenn H. Dillon
Journal of Pharmacology and Experimental Therapeutics September 1, 2001, 298 (3) 986-995;

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Research ArticleNEUROPHARMACOLOGY

Pentylenetetrazole-Induced Inhibition of Recombinant γ-Aminobutyric Acid Type A (GABAA) Receptors: Mechanism and Site of Action

Ren-Qi Huang, Cathy L. Bell-Horner, Mohammed I. Dibas, Douglas F. Covey, John A. Drewe and Glenn H. Dillon
Journal of Pharmacology and Experimental Therapeutics September 1, 2001, 298 (3) 986-995;
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