ENHANCEMENT OF GLYCINE RECEPTOR FUNCTION BY ETHANOL IS INVERSELY CORRELATED WITH MOLECULAR VOLUME AT POSITION ALPHA-267

Glycine and gamma-aminobutyric acid (GABA)(A) receptors are members of the ''superfamily'' of ion channels, and are sensitive to allosteric modulation by n-alcohols such as ethanol and butanol. We recently demo nstrated that the mutation of Ser-267 to Ile in the alpha 1 subunit ab olished ethanol regulation of glycine receptors (Gly-R). In the presen t study, a pair of chimeric receptors was studied, in which a 45-amino acid domain comprising transmembrane domains 2 and 3 was exchanged be tween the Gly-R alpha 1 and gamma-aminobutyric acid rho 1 subunits. De tailed pharmacologic analysis of these chimeras confirmed that this do main of the Gly-R confers enhancement of recep tor function by ethanol and butanol. An extensive series of mutations at Ser-267 in the Gly-R alpha 1 subunit was also prepared, and the resulting homomeric recept ors were expressed and tested for sensitivity to glycine, and alloster ic modulation by alcohols. All of the mutant receptors expressed succe ssfully in Xenopus oocytes. Mutation of Ser-267 to small amino acid re sidues such as Gly or Ala produced receptors in which glycine response s were potentiated by ethanol. As we have reported previously, the mut ant Gly-R alpha 1 (Ser-267 --> Ile) was completely insensitive to etha nol; mutation of Ser-267 to Val had a similar effect. Mutation of Ser- 267 to large residues such as His, Cys, or Tyr resulted in inhibition of Gly-R function by ethanol. These results demonstrate that the size of the amino acid residue at position alpha 267 plays a crucial role i n determining the functional consequences of allosteric modulation of the Gly-R by alcohols.