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.
Maggi
L
L
Department of Experimental Medicine and Pathology, Università di Roma La Sapienza, Rome, Italy.
Palma
E
E
Eusebi
F
F
Moretti
M
M
Balestra
B
B
Clementi
F
F
Gotti
C
C
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