Acute alcohol tolerance is intrinsic to the BKCa protein, but is modulated by the lipid environment
Paper in press, published online ahead of press December 15, 2007

Ethanol tolerance, in which exposure leads to reduced sensitivity, is an important component of alcohol abuse and addiction. The molecular mechanisms underlying this process remain poorly understood.

The BKCa channel plays a central role in the behavioral response to ethanol in C. elegans (1), and Drosophila (2). In neurons, ethanol tolerance in BKCa channels has two components: a reduced number of membrane channels, and decreased potentiation of the remaining channels (3).

Here, heterologous expression, coupled with planar bilayer techniques examines two additional aspects of tolerance in human BKCa channels: 1) Is acute tolerance observed in a single channel protein complex within a lipid environment reduced to only two lipids? 2) Does lipid bilayer composition affect the appearance of acute tolerance?

We found that tolerance was observable in BKCa channels in membrane patches pulled from HEK cells, and when they are placed into reconstituted POPE/POPS membranes. Further, altering bilayer thickness by incorporating the channel into lipid mixtures of DOPE with phosphatidylcholines (PCs) of increasing chain length, or with sphingomyelin (SPM), strongly affected the sensitivity of the channel, as well as the time course of the acute response. Ethanol sensitivity changed from a strong potentiation in thin bilayers, to inhibition in thick SPM/DOPE bilayers.

Thus, tolerance can be an intrinsic property of the channel protein/lipid complex, and bilayer thickness plays an important role in shaping the pattern of response to ethanol. As a consequence of these findings the protein/lipid complex should be treated as a unit when studying ethanol action.

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