Novel properties of homomeric beta 1 gamma-aminobutyric acid type A receptors: actions of the anesthetics propofol and pentobarbital.

In this study we determined the influence of gamma-aminobutyric acid (GABA)A receptor subunit composition on the direct effects of the general anesthetics propofol, pentobarbital, and alphaxalone, using recombinant receptors expressed in Xenopus oocytes. cDNAs coding for human beta 1, alpha 1 beta 1, or alpha 1 beta 1 gamma 2S GABAA receptor subunits were injected into Xenopus oocytes, and responses induced by either GABA or anesthetics were measured by two-electrode voltage-clamp recording. Expression of homomeric beta 1 receptors resulted in the formation of a Cl- channel that was sensitive to picrotoxin and strychnine and could be activated, albeit with relatively low potency, by GABA. However, GABA-induced currents of homomeric beta 1 receptors were completely insensitive to the GABAA receptor antagonist bicuculline. Homomeric beta 1 receptors showed marked direct activation by propofol or pentobarbital, but not by alphaxalone. In contrast, these three anesthetics induced much weaker direct activation of Cl- currents in oocytes expressing alpha 1 beta 1 or alpha 1 beta 1 gamma 2S receptors. These data indicate that the beta 1 subunit of the GABAA receptor forms a functional Cl- channel that contains sites for the direct activating effects of GABA, propofol, and pentobarbital and this GABA site is not blocked by bicuculline.