Synthesis And Characterization Of125I-Î±-Conotoxin Arib[V11L;V16A] A Selective Î±7 Nicotinic Acetylcholine Receptor Antagonist
The Î±7 nicotinic acetylcholine receptors (nAChRs) are widely expressed both in the central nervous system (CNS) and periphery. In the CNS, 125I-Î±-bungarotoxin is commonly used to identify Î±7 nAChRs specifically. However, Î±-bungarotoxin also interacts potently with Î±1* and Î±9Î±10 nAChRs, two receptor subtypes in peripheral tissues that are colocalized with the Î±7 subtype. [ 3H]Methyllycaconitine is also frequently used as an Î±7-selective antagonist, but it has significant affinity for Î±6* and Î±9Î±10 nAChR subtypes. In this study, we have developed a highly Î±7-selective Î±-conotoxin radioligand by iodination of a naturally occurring histidine. Both mono- and diiodo derivatives were generated and purified (specific activities were 2200 and 4400 Ci mmol-1, respectively). The properties of the mono- and diiodo derivatives were very similar to each other, but the diiodo was less stable. For monoidodo peptide, saturation binding to mouse hippocampal membranes demonstrated a Kd value of 1.15 Â± 0.13 nM, similar to that of 125I-Î±-bungarotoxin in the same preparations (0.52 Â± 0.16 nM). Association and dissociation kinetics were relatively rapid (k obs for association at 1 nM was 0.027 Â± 0.007 min -1; koff = 0.020 Â± 0.001 min-1). Selectivity was confirmed with autoradiography using Î±7-null mutant tissue: specific binding was abolished in all regions of Î±7-/- brains, whereas wild-type mice expressed high levels of labeling and low nonspecific binding. 125I-Î±-conotoxin ArIB[V11L; V16A] should prove useful where Î±7 nAChRs are coexpressed with other subtypes that are also labeled by existing ligands. Furthermore, true equilibrium binding experiments could be performed on Î±7 nAChRs, something that is impossible with 125I-Î±-bungarotoxin. Copyright Â© 2008 by The American Society for Pharmacology and Experimental Therapeutics.
Journal of Pharmacology and Experimental Therapeutics
Digital Object Identifier (DOI)
Whiteaker, Paul; Marks, Michael J.; Christensen, Sean; Dowell, Cheryl; Collins, Allan C.; and McIntosh, J. Michael, "Synthesis And Characterization Of125I-Î±-Conotoxin Arib[V11L;V16A] A Selective Î±7 Nicotinic Acetylcholine Receptor Antagonist" (2008). Neurobiology. 394.