Mode of action of the positive modulator PNU-120596 on α7 nicotinic acetylcholine receptors.
We investigated the mode of action of PNU-120596, a type II positive allosteric modulator of the rat α7 nicotinic acetylcholine receptor expressed by GH4C1 cells, using patch-clamp and fast solution exchange. We made two important observations: first, while PNU-120596 rapidly associated to desensitized receptors, it had at least hundredfold lower affinity to resting conformation, therefore at 10 μM concentration it dissociated from resting receptors; and second, binding of PNU-120596 slowed down dissociation of choline molecules from the receptor radically. We propose that when agonist concentration is transiently elevated in the continuous presence of the modulator (as upon the neuronal release of acetylcholine in a modulator-treated animal) these two elements together cause occurrence of a cycle of events: Binding of the modulator is limited in the absence of the agonist. When the agonist is released, it binds to the receptor, and induces desensitization, thereby enabling modulator binding. Modulator binding in turn traps the agonist within its binding site for a prolonged period of time. Once the agonist finally dissociated, the modulator can also dissociate without re-binding, and the receptor assumes its original resting conformation. In kinetic simulations this "trapped agonist cycle" mechanism did not require that the orthosteric and allosteric ligands symmetrically modify each other's affinity, only the modulator must decrease agonist accessibility, and the agonist must induce a conformation that is accessible to the modulator. This mechanism effectively prolongs and amplifies the effect of the agonist.
Semmelweis University, School of Ph.D. Studies, Üllői út 26, H-1085 Budapest, Hungary; Laboratory of Molecular Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O.B. 67, H-1450 Budapest, Hungary.
Anett K
AK
Szabo
Semmelweis University, School of Ph.D. Studies, Üllői út 26, H-1085 Budapest, Hungary; Laboratory of Molecular Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O.B. 67, H-1450 Budapest, Hungary.
Krisztina
K
Pesti
Laboratory of Molecular Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O.B. 67, H-1450 Budapest, Hungary. Electronic address: mike@koki.hu.
Arpad
A
Mike
Laboratory of Drug Research, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O.B. 67, H-1450 Budapest, Hungary.
E Sylvester
ES
Vizi
D000109:Acetylcholine / Q000494:pharmacology; D000494:Allosteric Regulation; D000818:Animals; D001703:Biophysics; D045744:Cell Line, Tumor; D002794:Choline / Q000494:pharmacology; D003198:Computer Simulation; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation; D007555:Isoxazoles / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects* / Q000235:genetics; D008954:Models, Biological; D018722:Nicotinic Agonists / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010671:Phenylurea Compounds / Q000494:pharmacology*; D010911:Pituitary Neoplasms / Q000473:pathology; D051381:Rats; D014162:Transfection; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000235:genetics / Q000378:metabolism*
C508388:1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)urea; D007555:Isoxazoles; D018722:Nicotinic Agonists; D010671:Phenylurea Compounds; D064569:alpha7 Nicotinic Acetylcholine Receptor; D002794:Choline; D000109:Acetylcholine
Choline; Mode of action; PNU-120596; Positive allosteric modulator; α7 nicotinic acetylcholine receptor