Distinct structural features of phospholipids differentially determine ethanol sensitivity and basal function of BK channels

Abstract

Large conductance Ca2+ -activated K+ (BK) channel activity and its potentiation by ethanol are both critically modulated by bilayer phosphatidylserine (PS), a phospholipid involved in membrane-bound signaling. Whether PS is uniquely required for ethanol to modify channel activity is unknown. Furthermore, the structural determinants in membrane phospholipid molecules that control alcohol action remain to be elucidated. We addressed these questions by reconstituting BK channels from human brain (hslo) into bilayers that contained phospholipids differing in headgroup size, charge, and acyl chain saturation. Data demonstrate that ethanol potentiation of hslo channels is blunted by conical phospholipids but favored by cylindrical phospholipids, independently of phospholipid charge. As found with ethanol action, basal channel activity is higher in bilayers containing cylindrical phospholipids. Basal activity and its ethanol potentiation in bilayers containing phosphatidylcholine, however, are not as robust as in those containing PS. These results are best interpreted as resulting from the relief of bilayer stress caused by inclusion of cylindrical phospholipids, with this relief being synergistically evoked by molecular shape and negative headgroup charge. Present findings suggest that hslo gating structures targeted by ethanol are accessible to sense changes in bilayer stress. In contrast, hslo unitary conductance is significantly higher in bilayers that contain negatively charged phospholipids independently of molecular shape, a result that is likely to be dependent on an interaction between anionic phospholipids and deep channel residues coupled to the selectivity filter.