Abstract

It is well known that ethanol modulates the function of the Cys loop ligand-gated ion channels, which include the inhibitory glycine receptors (GlyRs). Previous studies have consistently shown that transmembrane and extracellular sites are essential for ethanol actions in GlyRs. In addition, recent evidence has shown that the ethanol modulation of GlyRs is also affected by G protein activation through Gβγ subunits. However, more specific roles of G protein α subunits on ethanol actions are unknown. Here, we show that the allosteric effect of ethanol on the human α₁ GlyR is selectively enhanced by the expression of Gα_s Q-L. For example, constitutively active Gα_s, but not Gα_q or Gα_i, was able to displace the alcohol sensitivity of GlyRs toward low millimolar concentrations (17 ± 4 versus 48 ± 5% at 100 mM). Experiments under conditions that increased cAMP and protein kinase A (PKA)-mediated signaling, on the contrary, did not produce the same enhancement in sensitivity, suggesting that the Gα_s Q-L effect was not dependent on cAMP/PKA-dependent signaling. On the other hand, the effect of Gα_s Q-L was blocked by a Gβγ scavenger (9 ± 3% of control). Furthermore, two mutant receptors previously shown to have impaired interactions with Gβγ were not affected by Gα_s Q-L, suggesting that Gβγ is needed for enhancing ethanol sensitivity. These results support the conclusion that activated Gα_s can facilitate the Gβγ interaction with GlyRs in presence of ethanol, independent of increases in cAMP signaling. Thus, these data indicate that the activated form of Gα_s is able to positively influence the effect of ethanol on a type of inhibitory receptor important for motor control, pain, and respiration.