Gain of function mutation of the alpha 7 nicotinic receptor: distinct pharmacology of the human alpha 7V274T variant

In the human alpha 7 nicotinic receptor, valine-274 in the pore-lining tran smembrane-2 region was mutated to threonine to produce the variant human al pha 7V274T, which was evaluated electrophysiologically following expression in Xenopus laevis oocytes. Inward current rectification was strong in huma n alpha 7V274T as in the human alpha 7 wild type nicotinic receptor. Howeve r, human alpha 7V274T was 100-fold more sensitive to the nicotinic receptor agonists acetylcholine, (-)-nicotine and 1,1-dimethyl-4-phenylpiperazinium . Choline also activated human alpha 7V274T (EC50 = 12 mu M) and was 82-fol d more potent than at human alpha 7 wild type nicotinic receptor. (-)-Cotin ine, (2,4)-dimethoxybenzylidene anabaseine (GTS-21) and 2-methyl-3-(2-(S)-p yrrolidinylmethoxy)pyridine (ABT-089), weak partial agonists at human alpha 7 wild type, were much stronger agonists at human alpha 7V274T with EC50 v alues of 70 mu M, 4 mu M and 28 mu M and fractional activation values of 93 %, 96 % and 40 %, respectively. However, (-)-lobeline, a human alpha 7 wil d type nicotinic receptor antagonist, and dihydro-beta-erythroidine, which activates chick mutagenized alpha 7 nicotinic receptors, had only weak agon ist-like activity at human alpha 7V274T (less than or equal to 4 % of the m aximal acetylcholine response). Methyllycaconitine, mecamylamine, d-tubocur arine and dihydro-beta-erythroidine retained antagonist activity and, indee d, appeared to be at least as potent at human alpha 7V274T as at human alph a 7 wild type. These results support and extend the concept that human nico tinic receptor pharmacology can be profoundly altered by single amino acid changes in the pope-lining segment. (C) 1999 Elsevier Science B.V. All righ ts reserved.