Analogs of α-conotoxin PeIA Distinguish between α3β2 and α3β2β3 Nicotinic Acetylcholine Receptors

Parkinson’s is a neurodegenerative disease caused by the loss of dopaminergic neurons in the basal ganglia. Recent studies have shown that these neurons express several nicotinic acetylcholine receptor (nAChR) subtypes including those that contain α3, β2, and β3 subunits.  Identification of the subtypes that are lost in Parkinson’s has been hampered by the lack of ligands capable of distinguishing between closely related subtypes in general and in particular between the α3β2 and α3β2β3 subtypes. Previous work indicated that α-conotoxins, isolated from marine Conus snail venom, may be capable of discriminating between α3β2 and α3β2β3 nAChRs. We tested several these α-conotoxins on cloned human α3β2 and α3β2β3 nAChRs expressed in Xenopus laevis oocytes using two-electrode voltage-clamp electrophysiology. Our results show that α-conotoxins PeIA[N11A] and PeIA[L15A] discriminate between these two receptor subtypes. Both PeIA analogs were more potent at inhibiting α3β2 nAChRs. Additionally, linear regression analysis of the data for inhibition of α3β2β3 nAChRs by PeIA[N11A] was best fit using a two-site model and suggests that oocytes injected with α3, β2, and β3 cRNAs express a mixed population of α3β2 and α3β2β3 lending further support for the ability of these toxins to discriminate between the two subtypes. Data for inhibition of α3β2β3 nAChRs by PeIA[L15A] was best fit using a one-site model, however a residual response of 25 ± 2.3% (SEM) remained uninhibited indicating a loss of affinity for α3β2β3 nAChRs. Thus, these toxins may prove useful for identifying the nAChR subtypes that are concomitantly lost with basal ganglia neurons in Parkinson’s.