Selective effects of a 4-oxystilbene derivative on wild and mutant neuronal chick alpha7 nicotinic receptor.
1. We assessed the pharmacological activity of triethyl-(beta-4-stilbenoxy-ethyl) ammonium (MG624), a drug that is active on neuronal nicotinic receptors (nicotinic AChR). Experiments on the major nicotinic AChR subtypes present in chick brain, showed that it inhibits the binding of [125I]-alphaBungarotoxin (alphaBgtx) to the alpha7 subtype, and that of [3H]-epibatidine (Epi) to the alpha4beta2 subtype, with Ki values of respectively 106 nM and 84 microM. 2. MG624 also inhibited ACh elicited currents (I(ACh)) in the oocyte-expressed alpha7 and alpha4beta2 chick subtypes with half-inhibitory concentrations (IC50) of respectively 109 nM and 3.2 microM. 3. When tested on muscle-type AChR, it inhibited [125I]-alphaBgtx binding with a Ki of 32 microM and ACh elicited currents (I(ACh)) in the oocyte-expressed alpha1beta1gammadelta chick subtype with an IC50 of 2.9 microM. 4. The interaction of MG624 with the alpha7 subtype was investigated using an alpha7 homomeric mutant receptor with a threonine-for-leucine 247 substitution (L247T alpha7). MG624 did not induce any current in oocytes expressing the wild type alpha7 receptor, but did induce large currents in the oocyte-expressed L247T alpha7 receptor. The MG624 elicited current (I(MG62)) has an EC50 of 0.2 nM and a Hill coefficient nH of 1.9, and is blocked by the nicotinic receptor antagonist methyllycaconitine (MLA). 5. These binding and electrophysiological studies show that MG624 is a potent antagonist of neuronal chick alpha7 nicotinic AChR, and becomes a competitive agonist following the mutation of the highly conserved leucine residue 247 located in the M2 channel domain.
Department of Experimental Medicine and Pathology, Università di Roma La Sapienza, Rome, Italy.
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Maggi
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Palma
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Eusebi
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Moretti
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Balestra
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Clementi
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Gotti
D000109:Acetylcholine / Q000494:pharmacology; D019943:Amino Acid Substitution; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001667:Binding, Competitive / Q000187:drug effects; D002038:Bungarotoxins / Q000378:metabolism / Q000494:pharmacology; D002645:Chickens; D018678:Cholinergic Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D007120:Immunochemistry; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D009154:Mutation; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009865:Oocytes; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000494:pharmacology*; D011869:Radioligand Assay; D011978:Receptors, Nicotinic / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D013267:Stilbenes / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D014981:Xenopus; D064569:alpha7 Nicotinic Acetylcholine Receptor
D000109:Acetylcholine; D000906:Antibodies; D002038:Bungarotoxins; D018678:Cholinergic Agents; D000644:Quaternary Ammonium Compounds; D011978:Receptors, Nicotinic; D013267:Stilbenes; D064569:alpha7 Nicotinic Acetylcholine Receptor; C118602:triethyl-(beta-4-stilbenoxyethyl)ammonium