Fig. 1. Putative γ-aminobutyric acid type A (GABA^A) receptor subunit topology. GABA^Areceptor subunits have four hydrophobic transmembrane regions (TM1–TM4), a large hydrophilic ligand-binding domain in the extracellular N-terminus, 32an intracellular loop between TM3 and TM4, and a short extracellular C-terminus (top ). Amino acid sequence alignment of TM2 and TM3 from human α1, α2, β1, and β2 subunits (bottom ). Residue positions in bold type  within TM2 and TM3 of these receptor subunits are critical for potentiation of agonist responses by n-alcohols and volatile anesthetics. 3