TY - JOUR
T1 - Allosterically linked noncompetitive antagonist binding sites in the resting nicotinic acetylcholine receptor ion channel
AU - Arias, Hugo R.
AU - McCardy, Elizabeth A.
AU - Bayer, Erin Z.
AU - Gallagher, Martin J.
AU - Blanton, Michael P.
N1 - Funding Information:
We thank Dr. Jay Ponder (Washington University School of Medicine, St. Louis, MO) for use of his computer workstation, molecular graphics software, and invaluable assistance. This research was supported in part by National Institutes of Health Grant R29-NS35786 (M.P.B.).
PY - 2002/7/1
Y1 - 2002/7/1
N2 - Previous studies have established the presence of overlapping binding sites for the noncompetitive antagonists (NCAs) amobarbital, tetracaine, and 3-trifluoromethyl-3-(m-[125I]iodophenyl) diazirine ([125I]TID) within the ion channel of the Torpedo nicotinic acetylcholine receptor (AChR) in the resting state. These well-characterized NCAs and competitive radioligand binding and photolabeling experiments were employed to better characterize the interaction of the dissociative anesthetics ketamine and thienylcycloexylpiperidine (TCP) with the resting AChR. Our experiments yielded what appear to be conflicting results: (i) both ketamine and TCP potentiated [125I]TID photoincorporation into AChR subunits; and (ii) ketamine and TCP had very little effect on [14C]amobarbital binding. Nevertheless, (iii) both ketamine and TCP completely displaced [3H]tetracaine binding (Kis ∼ 20.9 and 2.0 μM, respectively) by a mutually exclusive mechanism. To reconcile these results we propose that, in the resting ion channel, TCP and ketamine bind to a site that is spatially distinct from the TID and barbiturate locus, while tetracaine bridges both binding sites.
AB - Previous studies have established the presence of overlapping binding sites for the noncompetitive antagonists (NCAs) amobarbital, tetracaine, and 3-trifluoromethyl-3-(m-[125I]iodophenyl) diazirine ([125I]TID) within the ion channel of the Torpedo nicotinic acetylcholine receptor (AChR) in the resting state. These well-characterized NCAs and competitive radioligand binding and photolabeling experiments were employed to better characterize the interaction of the dissociative anesthetics ketamine and thienylcycloexylpiperidine (TCP) with the resting AChR. Our experiments yielded what appear to be conflicting results: (i) both ketamine and TCP potentiated [125I]TID photoincorporation into AChR subunits; and (ii) ketamine and TCP had very little effect on [14C]amobarbital binding. Nevertheless, (iii) both ketamine and TCP completely displaced [3H]tetracaine binding (Kis ∼ 20.9 and 2.0 μM, respectively) by a mutually exclusive mechanism. To reconcile these results we propose that, in the resting ion channel, TCP and ketamine bind to a site that is spatially distinct from the TID and barbiturate locus, while tetracaine bridges both binding sites.
KW - Conformational states
KW - Equilibrium binding
KW - Ketamine and phencyclidine binding sites
KW - Photoaffinity labeling
KW - Torpedo nicotinic acetylcholine receptor
UR - http://www.scopus.com/inward/record.url?scp=0036646949&partnerID=8YFLogxK
U2 - 10.1016/S0003-9861(02)00214-X
DO - 10.1016/S0003-9861(02)00214-X
M3 - Article
C2 - 12061809
AN - SCOPUS:0036646949
SN - 0003-9861
VL - 403
SP - 121
EP - 131
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
IS - 1
ER -