Flunitrazepam has an inverse agonistic effect on recombinant α₆β₂γ₂-GABA(A) receptors via a flunitrazepam-binding site

γ-Aminobutyric acid type A (GABA(A)) receptor subtypes containing the α₆-subunit are generally thought to be insensitive to the action of benzodiazepine agonists. We describe the specific binding of the benzodiazepine agonist flunitrazepam to α₆β₂γ₂-containing GABA(A) receptors, which has not been observed before and differs from previous reports. With the whole-cell voltage-clamp technique, we observed a functional discrimination between α₁β₂γ₂ and α₆β₂γ₂-receptors. Different benzodiazepines had different effects on GABA-evoked chloride currents. The agonist flunitrazepam had an inverse agonistic effect, whereas the antagonist flumazenil increased GABA-induced chloride currents. The action of flunitrazepam on the channel activity of α₆β₂γ₂-receptors was opposite to its action on α₁β₂γ₂-receptors. We conclude that flunitrazepam can act as either an agonist or an inverse agonist, depending on the GABA(A) receptor configuration.