The observations that mutations at the hydrophobic pocket did not alter alcohol-dependent inhibition of IRK1, and that S148T mutation (but not L257W) in GIRK2-PIP2 decreased alcohol-dependent inhibition suggest that GIRK channels possess two different sites for alcohol modulation. In the Kirbac1.3 structure, the Ser is located in the pore helix of Kirbac1.3 where there is no space for alcohol (Supplemental Fig. S4), suggesting that S148 regulates the sensitivity to inhibition but does not form the binding site. Alcohols might interfere with ion permeation or possibly with gating at the transmembrane domains, similar to voltage-gated K channels9. Another possibility is that alcohols inhibit the channel by altering the fluidity of the lipid membrane5 and/or decreasing interactions with phospholipid phosphatidylinositol bisphosphate (PIP2), which is required for channel function31.
