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

Abstract

In the human α7 nicotinic receptor, valine-274 in the pore-lining transmembrane-2 region was mutated to threonine to produce the variant human α7V274T, which was evaluated electrophysiologically following expression in Xenopus laevis oocytes. Inward current rectification was strong in human α7V274T as in the human α7 wild type nicotinic receptor. However, human α7V274T was 100-fold more sensitive to the nicotinic receptor agonists acetylcholine, (−)-nicotine and 1,1-dimethyl-4-phenylpiperazinium. Choline also activated human α7V274T (EC 50=12 μM) and was 82-fold more potent than at human α7 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 α7 wild type, were much stronger agonists at human α7V274T with EC 50 values of 70 μM, 4 μM and 28 μM and fractional activation values of 93%, 96% and 40%, respectively. However, (−)-lobeline, a human α7 wild type nicotinic receptor antagonist, and dihydro-β-erythroidine, which activates chick mutagenized α7 nicotinic receptors, had only weak agonist-like activity at human α7V274T (≤4% of the maximal acetylcholine response). Methyllycaconitine, mecamylamine, d-tubocurarine and dihydro-β-erythroidine retained antagonist activity and, indeed, appeared to be at least as potent at human α7V274T as at human α7 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 pore-lining segment.