Gain of function mutation of the α7 nicotinic receptor:: distinct pharmacology of the human α7V274T variant

In the human alpha 7 nicotinic receptor, valine-274 in the pore-lining transmembrane-2 region was mutated to threonine to produce the variant human alpha 7V274T, which was evaluated electrophysiologically following expression in Xenopus laevis oocytes. Inward current rectification was strong in human alpha 7V274T as in the human alpha 7 wild type nicotinic receptor. However, 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-fold more potent than at human alpha 7 wild type nicotinic receptor. (-)-Cotinine, (2,4)-dimethoxybenzylidene anabaseine (GTS-21) and 2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine (ABT-089), weak partial agonists at human alpha 7 wild type, were much stronger agonists at human alpha 7V274T with EC50 values 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 wild type nicotinic receptor antagonist, and dihydro-beta-erythroidine, which activates chick mutagenized alpha 7 nicotinic receptors, had only weak agonist-like activity at human alpha 7V274T (less than or equal to 4 % of the maximal acetylcholine response). Methyllycaconitine, mecamylamine, d-tubocurarine and dihydro-beta-erythroidine retained antagonist activity and, indeed, appeared to be at least as potent at human alpha 7V274T as at human alpha 7 wild type. These results support and extend the concept that human nicotinic receptor pharmacology can be profoundly altered by single amino acid changes in the pope-lining segment. (C) 1999 Elsevier Science B.V. All rights reserved.