Characterization of the Dizocilpine Binding Site on the Nicotinic Acetylcholine Receptor
Although the dissociative anesthetic dizocilpine [(+)-MK-801] inhibits nicotinic acetylcholine receptor (AChR) function in a noncompetitive manner, the location of the dizocilpine binding site(s) has yet to be clearly established. Thus, to characterize the binding site for dizocilpine on the AChR we...
Saved in:
Published in | Molecular pharmacology Vol. 59; no. 5; pp. 1051 - 1060 |
---|---|
Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
United States
American Society for Pharmacology and Experimental Therapeutics
01.05.2001
|
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | Although the dissociative anesthetic dizocilpine [(+)-MK-801] inhibits nicotinic acetylcholine receptor (AChR) function in
a noncompetitive manner, the location of the dizocilpine binding site(s) has yet to be clearly established. Thus, to characterize
the binding site for dizocilpine on the AChR we examined 1) the dissociation constant ( K
d ) and stoichiometry of [ 3 H]dizocilpine binding; 2) the displacement of dizocilpine radioligand binding by noncompetitive inhibitors (NCIs) and conversely
dizocilpine displacement of fluorescent and radiolabeled NCIs from their respective high-affinity binding sites on the AChR;
and 3) photoaffinity labeling of the AChR using 125 I-dizocilpine. The results establish that one high-affinity ( K
d = 4.8 μM) and several (3â6) low-affinity ( K
d = â¼140 μM) binding sites exist for dizocilpine on the desensitized and resting AChR, respectively. The binding of the fluorescent
NCIs ethidium, quinacrine, and crystal violet as well as [ 3 H]thienylcyclohexylpiperidine was inhibited by dizocilpine on desensitized AChRs. However, Schild-type analyses indicate that
only the inhibition of quinacrine in the desensitized state seems to be mediated by a mutually exclusive action. Photoaffinity
labeling of the AChR by 125 I-dizocilpine was primarily restricted to the α1 subunit and subsequent mapping revealed that the principal sites of labeling
are localized to the M4 (â¼70%) and M1 (30%) transmembrane domains. Collectively, the data indicate that the high-affinity
dizocilpine binding site is not located in the lumen of the ion channel but probably near the quinacrine binding locus at
a nonluminal domain in the AChR desensitized state. |
---|---|
Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0026-895X 1521-0111 |
DOI: | 10.1124/mol.59.5.1051 |