PT  - JOURNAL ARTICLE
AU  - Can Peng
AU  - Matthew R. Kimbrell
AU  - Chengju Tian
AU  - Thomas F. Pack
AU  - Peter A. Crooks
AU  - E. Kim Fifer
AU  - Roger L. Papke
TI  - Multiple modes of α7 nAChR non-competitive antagonism of control agonist-evoked and allosterically enhanced currents
AID  - 10.1124/mol.113.086462
DP  - 2013 Jul 09
TA  - Molecular Pharmacology
PG  - mol.113.086462
4099  - http://molpharm.aspetjournals.org/content/early/2013/07/09/mol.113.086462.short
4100  - http://molpharm.aspetjournals.org/content/early/2013/07/09/mol.113.086462.full
AB  - Positive allosteric modulators (PAMs) of α7 nicotinic acetylcholine receptors can enhance ion channel currents and downstream effects of α7 stimulation. We investigated the approach of using non-competitive antagonists to regulate α7 receptor function, potentially distinguishing effects requiring ion channel currents from signaling induced by non-conducting states. Three small readily reversible antagonists, mecamylamine, QX-314, and tetracaine, as well as three large slowly reversible antagonists, BTMPS, TMPH, and tkP3BzPB, were investigated for their effectiveness and voltage dependence in the inhibition of responses evoked by acetylcholine alone or augmented by the α7-selective PAM PNU-120596. Analyses of the small antagonists on PNU-120596-potentiated single-channel bursts indicated that each agent had a distinct mechanism of inhibition and only that of QX-314 was consistent with simple open-channel block. In addition to decreasing channel open times and burst durations, mecamylamine and tetracaine induced unique subconductance states. In order to determine if channel blocking activity alone would be sufficient to prevent cell death, the antagonists were tested for their ability to protect α7-expressing cells from cytotoxic effects of the α7 agonist choline in combination with PNU-120596. Only tetracaine and tkP3BzPB, the two agents which had effects least consistent with simple ion channel block, were fully cytoprotective at concentrations that gave submaximal inhibition of macroscopic currents in oocytes. Further analyses indicated that toxicity produced by PNU-120596 and choline was calcium independent and likely an apoptotic event. Our results are consistent with the hypothesis that PAMs may modulate conformational states important for both channel activity and ion channel-independent signaling.