GABAA receptor antagonist that binds the picrotoxin site and stabilizes the inactive form of the channel via allosteric interaction. Accelerates the decay of GABA-induced Cl- currents with little effect on peak amplitude. Also inhibits 5-HT3A receptors via a similar mechanism.

GABAA:100 nM

In the presence of U93631 at 5 UM, the peak amplitude decreased as a function of GABA concentration, with the half-maximal inhibitory concentration being approximately 100 nM, which is close to the Kd for the high affinity GABA site(85 nM). It appears that the drug interacts with GABA-bound receptors (at least monoliganded) and accelerates receptor desensitization, rather than acting as an open channel blocker.