Interaction of ibogaine with human alpha3beta4-nicotinic acetylcholine receptors in different conformational states.
The interaction of ibogaine and phencyclidine (PCP) with human (h) alpha3beta4-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)3beta4 AChRs with approximately 9-fold higher potency than that for PCP, (b) 3Hibogaine binds to a single site in the h(alpha)3beta4 AChR ion channel with relatively high affinity (Kd 0.46 - 0.06 microM), and ibogaine inhibits 3Hibogaine binding to the desensitized h(alpha)3beta4 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 3Hibogaine binding to the h(alpha)3beta4 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 valinephenylalanine (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 valinephenylalanine 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.