PT  - JOURNAL ARTICLE
AU  - Ren-Qi Huang
AU  - Cathy L. Bell-Horner
AU  - Mohammed I. Dibas
AU  - Douglas F. Covey
AU  - John A. Drewe
AU  - Glenn H. Dillon
TI  - Pentylenetetrazole-Induced Inhibition of Recombinant γ-Aminobutyric Acid Type A (GABA<sub>A</sub>) Receptors: Mechanism and Site of Action
DP  - 2001 Sep 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 986--995
VI  - 298
IP  - 3
4099  - http://jpet.aspetjournals.org/content/298/3/986.short
4100  - http://jpet.aspetjournals.org/content/298/3/986.full
SO  - J Pharmacol Exp Ther2001 Sep 01; 298
AB  - 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. The American Society for Pharmacology and Experimental Therapeutics