Acute Alcohol Tolerance Is Intrinsic to the BKCa Protein, but Is Modulated by the Lipid EnvironmentJ. Biol. Chem., Vol. 283, Issue 8, 5090-5098, February 22, 2008
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 BK
Ca channel plays a central role in the behavioral response
to ethanol in
Caenorhabditis elegans and
Drosophila .
In neurons, ethanol
tolerance in BK
Ca channels has two components: a reduced number
of membrane channels and decreased potentiation of the remaining
channels
.
Here, heterologous expression coupled with
planar bilayer techniques examines two additional aspects of
tolerance in human BK
Ca 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 BK
Ca channels in membrane patches pulled from
HEK cells and when they are placed into reconstituted 1-palmitoyl-2-oleoyl-
sn-glycero-3-phosphatidylethanolamine/1-palmitoyl-2-oleoyl-
sn-glycero-3-phosphatidylserine
membranes. Furthermore, altering bilayer thickness by incorporating
the channel into lipid mixtures of 1,2-dioleoyl-3-phosphatidylethanolamine
with phosphatidylcholines of increasing chain length, or with
sphingomyelin, 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 sphingomyelin/1,2-dioleoyl-3-phosphatidylethanolamine
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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