Interaction of ibogaine with human α3β4-nicotinic acetylcholine receptors in different conformational states

The interaction of ibogaine and phencyclidine (PCP) with human (h) alpha 3 beta 4-nicotinic acetylcholine receptors (AChRs) in different conformational states was determined by functional and structural approaches including, radioligand binding assays, Ca2+ influx detections, and thermodynamic and kinetics measurements. The results established that (a) ibogaine inhibits (+/-)-epibatidine-induced Ca2+ influx in h alpha 3 beta 4 AChRs with similar to 9-fold higher potency than that for PCP, (b) [H-3]ibogaine binds to a single site in the 1106134 AChR ion channel with relatively high affinity (K-d = 0.46 +/- 0.06 mu M), and ibogaine inhibits [H-3]ibogaine binding to the desensitized h alpha 3 beta 4 AChR with slightly higher affinity compared to the resting AChR. This is explained by a slower dissociation rate from the desensitized ion channel compared to the resting ion channel, and (c) PCP inhibits [H-3]ibogaine binding to the h alpha 3 beta 4 AChR, suggesting overlapping sites. The experimental results correlate with the docking simulations suggesting that ibogaine and PCP interact with a binding domain located between the serine (position 6') and valine/phenylalanine (position 13') rings. This interaction is mediated mainly by van der Waals contacts, which is in agreement with the observed enthalpic contribution determined by non-linear chromatography. However, the calculated entropic contribution also indicates local conformational changes. Collectively our data suggest that ibogaine and PCP bind to overlapping sites located between the serine and valine/phenylalanine rings, to finally block the AChR ion channel, and in the case of ibogaine, to probably maintain the AChR in the desensitized state for longer time. (C) 2010 Elsevier Ltd. All rights reserved.