TY - JOUR T1 - Nicotinic acetylcholine receptor transmembrane mutations convert ivermectin from a positive to a negative allosteric modulator JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.110.064295 SP - mol.110.064295 AU - Toby Collins AU - Neil S. Millar Y1 - 2010/05/12 UR - http://molpharm.aspetjournals.org/content/early/2010/05/12/mol.110.064295.abstract N2 - Ivermectin is a macrocyclic lactone that acts as a positive allosteric modulator of α7 nicotinic acetylcholine receptors (nAChRs) but has no modulatory activity on 5-hydroxytryptamine (5-HT) type 3 (5-HT3) receptors. By examining the influence of ivermectin on subunit chimeras containing domains from the nAChR α7 subunit and 5-HT3A subunit, we have concluded that the transmembrane domains play a critical role in influencing allosteric modulation by ivermectin. A series of mutations located within the α-helical transmembrane domains of the α7 subunit were examined and seven were found to have significant effects on allosteric modulation by ivermectin. Four mutations (A225D, Q272V, T456Y and C459Y) caused a significant reduction in the potency of ivermectin as an allosteric potentiator. Compared to wildtype α7 nAChRs, potentiation by ivermectin was reduced dramatically (by between 89% and 97%) by these mutations. Somewhat unexpectedly, three mutations (S222M, M253L and S276V; located in TM1, TM2 and TM3) converted ivermectin from a positive allosteric modulator into an antagonist. Levels of inhibition of 56%, 84% and 89% were observed on M253L, S276V and S222M, respectively. Antagonism by ivermectin was non-surmountable and had no effect on EC50 of acetylcholine, indicating that it is acting non-competitively. The seven mutations that influence allosteric modulation by ivermectin are located close to a predicted intra-subunit transmembrane cavity. Computer docking simulations provide support for the hypothesis that ivermectin binds in close proximity to this cavity. We conclude that transmembrane mutations in α7 nAChRs are able to convert ivermectin from a positive to a negative allosteric modulator.The American Society for Pharmacology and Experimental Therapeutics ER -