[Abstract Title]. - Society for Neuroscience

Poster
233. Nicotinic Aacetylcholine Receptors: Regulation and Function II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 233.4/C6
Topic: B.02.c. Nicotinic acetylcholine receptors: regulation and function
Title: A single amino acid substitution in the β9 strand of rat α7 nicotinic receptor which slows
desensitization
Authors: T. MCCORMACK, E. A. GAY, *J. L. YAKEL;
Lab. of Neurobio., NIEHS F2-08, Res Triangle Pk, NC
Abstract: The α7 subtype of nicotinic acetylcholine receptors (nAChRs) is widely recognized as
a potential therapeutic target for the treatment of a variety of pathologic conditions, including
schizophrenia, and Alzheimer's disease. One unique feature of α7 nAChRs that complicates
functional assays, which would help identify selective drugs for these receptors, is the rapid
desensitization of the agonist-evoked responses. A region of the ligand-binding pocket that is
thought to move when agonist binds to the α7 nAChR is the F-loop (also known as the β8-β9
linker). Whether and/or how this region interacts with other regions of the ligand-binding pocket
and affects channel function is unknown. When the proline residue at position 180 (P180) in the
β9 strand was mutated to a threonine residue (P180T), we observed a much slower rate of
receptor desensitization; the half-time of decay increased from 111 ± 7 msec for wildtype to
1260 ± 86 msec for the P180T mutation. In addition the EC50 value decreased to 56 κM for the
mutant versus 120 κM for wildtype. When P180 was mutated to glycine, the channels‟
desensitization rate (242 ± 44 msec) was much closer to that of wildtype. Mutation of P180 to
cysteine produced a decrease in peak current response to ACh and covalent modification of the
mutant C180 with various MTS reagents (e.g. MTSEA) was also tested in order to investigate
the effect of sulfhydryl reagents on channel function; however these reagents had no significant
effect on channel function. Considering that α7 homology models consistently predict that the
position 180 sidechain projects outward into the aqueous environment and thus should be
accessible to covalent modification, we would predict that these MTS molecules are covalently
modifying the C180 residue but with no noticeable effect on channel function. Together these
data would suggest that the size, shape, and/or post-translational modification of the threonine
residue at position 180, and not just the absence of the endogenous proline residue at this
position, confers slow desensitization. Furthermore the P180T α7 mutation, unlike the α7-L248T
gain-of-function mutant, exhibits properties that are remarkably similar to the wild-type α7
receptor (except for desensitization onset), implicating it as a useful tool for identifying
therapeutic agents targeting the α7 nAChR.