January 1999, Volume 126, Issue 1, Pages 285 - 295

Original Article

Selective effects of a 4-oxystilbene derivative on wild and mutant neuronal chick 7 nicotinic receptor L. Maggi1, E. Palma1, F. Eusebi1, M. Moretti2, B. Balestra2, F. Clementi2 & C. Gotti2,3 1Department of Experimental Medicine and Pathology, Università di Roma `La Sapienza' e Laboratorio di Biofisica CRS, IRE, via delle Messi d'Oro 156, Rome, Italy     2CNR Center of Cellular and Molecular Pharmacology, Department of Medical Pharmacology, University of Milan, Via Vanvitelli 32, 20129, Milan, Italy     3Author for correspondence: E-mail: gotti@farma4.csfic.mi.cnr.it

Keywords

MG624;   neuronal nicotinic receptors;   muscle nicotinic receptors;   subtypes;   Bungarotoxin;   epibatidine;   methyllycaconitine;   oocytes;   chick

Abstract

1   We assessed the pharmacological activity of triethyl-(-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]-Bungarotoxin (Bgtx) to the 7 subtype, and that of [3H]-epibatidine (Epi) to the 42 subtype, with Ki values of respectively 106 nM and 84 µM. 2   MG624 also inhibited ACh elicited currents (IACh) in the oocyte-expressed 7 and 42 chick subtypes with half-inhibitory concentrations (IC50) of respectively 109 nM and 3.2 µM. 3   When tested on muscle-type AChR, it inhibited [125I]-Bgtx binding with a Ki of 32 µM and ACh elicited currents (IACh) in the oocyte-expressed 11 chick subtype with an IC50 of 2.9 µM. 4   The interaction of MG624 with the 7 subtype was investigated using an 7 homomeric mutant receptor with a threonine-for-leucine 247 substitution (L247T 7). MG624 did not induce any current in oocytes expressing the wild type 7 receptor, but did induce large currents in the oocyte-expressed L247T 7 receptor. The MG624 elicited current (IMG624) 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 7 nicotinic AChR, and becomes a competitive agonist following the mutation of the highly conserved leucine residue 247 located in the M2 channel domain.

Received 8 August 1998; Revised 14 October 1998; Accepted 15 October 1998

^© Macmillan Publishers Ltd 1999