RT Journal Article SR Electronic T1 Synthesis and Characterization of 125I-α-Conotoxin ArIB[V11L;V16A], a Selective α7 Nicotinic Acetylcholine Receptor Antagonist JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 910 OP 919 DO 10.1124/jpet.108.136895 VO 325 IS 3 A1 Paul Whiteaker A1 Michael J. Marks A1 Sean Christensen A1 Cheryl Dowell A1 Allan C. Collins A1 J. Michael McIntosh YR 2008 UL http://jpet.aspetjournals.org/content/325/3/910.abstract AB The α7 nicotinic acetylcholine receptors (nAChRs) are widely expressed both in the central nervous system (CNS) and periphery. In the CNS, 125I-α-bungarotoxin is commonly used to identify α7 nAChRs specifically. However, α-bungarotoxin also interacts potently with α1* and α9α10 nAChRs, two receptor subtypes in peripheral tissues that are colocalized with the α7 subtype. [3H]Methyllycaconitine is also frequently used as an α7-selective antagonist, but it has significant affinity for α6* and α9α10 nAChR subtypes. In this study, we have developed a highly α7-selective α-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 ± 0.13 nM, similar to that of 125I-α-bungarotoxin in the same preparations (0.52 ± 0.16 nM). Association and dissociation kinetics were relatively rapid (kobs for association at 1 nM was 0.027 ± 0.007 min-1; koff = 0.020 ± 0.001 min-1). Selectivity was confirmed with autoradiography using α7-null mutant tissue: specific binding was abolished in all regions of α7-/- brains, whereas wild-type mice expressed high levels of labeling and low nonspecific binding. 125I-α-conotoxin ArIB[V11L; V16A] should prove useful where α7 nAChRs are coexpressed with other subtypes that are also labeled by existing ligands. Furthermore, true equilibrium binding experiments could be performed on α7 nAChRs, something that is impossible with 125I-α-bungarotoxin. The American Society for Pharmacology and Experimental Therapeutics