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Vol. 60, Issue 4, 700-711, October 2001
Department of Molecular Pharmacology and Biological Chemistry,
Northwestern University Medical School, Chicago, Illinois (Y.Z.,
G.L.A., W.M., J.Z.Y., T.N.); and Merck Research Laboratories-San
Diego, La Jolla, California (A.G., L.E.C.-N.)
Alcohol is known to modulate the activity of a variety of
neuroreceptors and ion channels. Recently, neuronal nicotinic
acetylcholine receptors (nnAChRs) have become a specific focus of study
because not only are they potently modulated by alcohol but also they regulate the release of various transmitters, including
-aminobutyric acid (GABA) and dopamine, which play an important role
in the behavioral effects of ethanol. Whereas the potency of normal
alcohols (n-alcohols) to potentiate GABAA
receptors and to inhibit
N-methyl-D-aspartate receptors
increases with carbon chain length, we have found that n-alcohols, depending on the carbon chain length, exert
a dual action, potentiation and inhibition, on nnAChRs in primary
cultured rat cortical neurons. The mechanism of dual action of
n-alcohols on nnAChRs was further analyzed using human
embryonic kidney cells expressing the
4
2 subunits. Shorter chain
alcohols from methanol to n-propanol potentiated
acetylcholine (ACh)-induced currents, whereas longer chain alcohols
from n-pentanol to n-dodecanol inhibited the currents. n-Butanol either potentiated or inhibited
the currents depending on the concentrations of ACh and butanol. The
parameters for both potentiation (log EC200) and
inhibition (log IC50) were linearly related to carbon
number, albeit with different slopes. The slope for potentiation was
0.299, indicating a change in free energy change (
G) of 405 cal/mol/methylene group, whereas the slope for inhibition was
0.584,
indicating a 
G of 792 cal/mol. These results suggest that
potentiating and inhibitory actions are exerted through two different
binding sites. Ethanol decreased the potency of
n-octanol to inhibit ACh currents, possibly resulting from an allosteric mechanism.
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