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Interaction of benzylidene‐anabaseine analogues with agonist and allosteric sites on muscle nicotinic acetylcholine receptors
Author(s) -
Arias HR,
Xing H,
MacDougall K,
Blanton MP,
Soti F,
Kem WR
Publication year - 2009
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2009.00156.x
Subject(s) - chemistry , agonist , allosteric regulation , partial agonist , nicotinic agonist , acetylcholine receptor , nicotinic acetylcholine receptor , competitive antagonist , pharmacology , dizocilpine , phencyclidine , acetylcholine , antagonist , stereochemistry , receptor , biochemistry , biology , nmda receptor
Background and purpose: Benzylidene‐anabaseines (BAs) are partial agonists of the α7 nicotinic acetylcholine receptor (nAChR) but their mechanism(s) of action are unknown. Our study explores several possibilities, including direct interactions of BAs with the nAChR channel. Experimental approach: Functional and radioligand‐binding assays were used to examine the interaction of two BA analogues, 3‐(2,4‐dimethoxybenzylidene)‐anabaseine (DMXBA) and its primary metabolite 3‐(4‐hydroxy‐2‐methoxybenzylidene)‐anabaseine (4OH‐DMXBA) with both agonist and non‐competitive antagonist (NCA)‐binding sites on muscle‐type nAChRs. Key results: Both BAs non‐competitively inhibited ACh activation of human fetal muscle nAChRs and sterically inhibited the specific binding of the NCAs [piperidyl‐3,4‐3H( N )]‐( N ‐(1‐(2‐thienyl)cyclohexyl)‐3,4‐piperidine ([ 3 H]TCP) and [ 3 H]dizocilpine to Torpedo nAChRs in the desensitized state. These compounds modulated [ 3 H]tetracaine, [ 14 C]amobarbital and [ 3 H]TCP binding to resting nAChRs by allosteric mechanisms. Both BAs enhanced [ 3 H]TCP binding when the nAChR was initially in the resting but activatable state, suggesting that both compounds desensitized the Torpedo nAChR. Although DMXBA failed to activate human fetal muscle nAChRs, 4OH‐DMXBA was found to be a partial agonist. [ 3 H]Nicotine competition‐binding experiments confirmed that 4OH‐DMXBA has higher affinity than DMXBA for the agonist sites, and that DMXBA is also a competitive antagonist. Conclusions and implications: 3‐(4‐hydroxy‐2‐methoxybenzylidene)‐anabaseine is a partial agonist for human fetal muscle nAChRs, whereas DMXBA only has competitive and NCA activities. The NCA‐binding site for BAs overlaps both the phencyclidine‐ and dizocilpine‐binding sites in the desensitized Torpedo nAChR ion channel. The desensitizing property of BAs suggests another possible mode of non‐competitive inhibition in addition to direct channel‐blocking mechanisms.