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Vol. 63, Issue 2, 419-428, February 2003
7-Containing Nicotinic Acetylcholine Receptors
by Select Albumins
Neurobiology Section, Division of Biological Sciences, University
of California, San Diego, La Jolla, California (W.G.C., Q.-S.L.,
D.K.B.); and Department of Anatomy and Neurobiology; Medical College of
Ohio; Toledo, Ohio (Q.N., J.F.M.)
Nicotinic receptors containing
7 subunits are ligand-gated ion
channels widely distributed in the nervous system; they influence a
diverse array of events because of their high relative calcium permeability. We show here that nicotine-induced whole-cell responses generated by such receptors can be dramatically potentiated in a
rapidly reversible manner by some but not all albumins. The potentiation involves increases both in potency and efficacy with no
obvious differences in rise and fall times of the response. The
potentiation is not reduced by removing absorbed components; it is
abolished by proteolysis, suggesting that the albumin protein backbone
is essential. The fact that some albumins are ineffective indicates
that minor differences in amino acid sequence may be critical.
Experiments with open channel blockers indicate that the potentiation
involves increased responses from active receptors rather than
recruitment of receptors from a previously silent pool. Single channel
recordings reveal that the potentiation correlates with increased
single channel opening probability, reflected in increased frequency of
channel opening and increased mean channel open time. The potentiation
can be exploited to overcome blockade by noncompetitive inhibitors such
as
-amyloid peptide. The results raise the possibility that
endogenous compounds use the site to modulate receptor function in
vivo, and suggest that the receptors may represent useful targets for
therapeutic intervention in cases where they have been implicated in
neuropathologies such as Alzheimer's disease.
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