Competitive antagonists facilitate the recovery from desensitization of α1β2γ2 GABAA receptors expressed in Xenopus oocytes

Abstract

Aim:The continuous presence of an agonist drives its receptor into a refractory state, termed desensitization. In this study, we tested the hypothesis that a competitive antagonist, SR95531, could facilitate the recovery of α1β2γ2 GABA A receptor from functional desensitization. Methods: α1β2γ2 GABA A receptors were expressed in Xenopus oocytes. GABA-evoked currents were recorded using two-electrode voltage-clamp technique. Drugs were applied through perfusion. Results: Long application of GABA (100 µmol/L) evoked a large peak current followed by a small amplitude steady-state current (desensitization). Co-application of SR95531 during the desensitization caused a larger rebound of GABA current after removal of SR95531. Furthermore, application of SR95531 after removal of GABA increased the rate of receptor recovery from desensitization, and the recovery time constant was decreased from 59±3.2 s to 33±1.6 s. SR95531-facilitated receptor recovery from desensitization was dependent on the perfusion duration of SR95531. It was also dependent on the concentration of SR95531, and the curve fitting with Hill equation revealed two potency components, which were similar to the two potency components in inhibition of the steadystate current by SR95531. Bicuculline caused similar facilitation of desensitization recovery. Conclusion: SR95531 facilitates α1β2γ2 GABA A receptor recovery from desensitization, possibly through two mechanisms: binding to the desensitized receptor and converting it to the non-desensitized state, and binding to the resting state receptor and preventing re-desensitization.

The Sulfated Steroids Pregnenolone Sulfate and Dehydroepiandrosterone Sulfate Inhibit the α1β3γ2L GABAA Receptor by Stabilizing a Novel Nonconducting State

“…Fitting the fractional recovery from GABA-induced desensitization over time to a singleexponential function gave a time constant of 81 ± 6 s. This is similar to recovery from desensitization reported previously (Chang et al, 2002;Xu et al, 2016).…”

GABAA receptor signalling mechanisms revealed by structural pharmacology

“…Another broadly used GABA A R antagonist, BCC, is thought to act competitively. However, the BCC preference to bind resting over desensitized receptors suggests that it might also act allosterically27. Where do important reagents like PTX and BCC actually bind, and how do they work?…”

The dual‐gate model for pentameric ligand‐gated ion channels activation and desensitization

“…At sub-activating agonist concentrations, picrotoxin also promotes agonist dissociation by stabilizing the resting conformation, as shown by voltage-clamp fluorometry of GABA A Rs . It could thus be argued that the rebound current observed upon picrotoxin wash-out could actually reflect the stabilization of the resting state over the active state, similarly to competitive antagonists (Xu et al 2016), rather than preventing desensitization.…”

“…It could thus be argued that the rebound current observed upon picrotoxin wash‐out could actually reflect the stabilization of the resting state over the active state, similarly to competitive antagonists (Xu et al . ), rather than preventing desensitization.…”