Specificity, affinity and efficacy of iota-conotoxin RXIA, an agonist of voltage-gated sodium channels Na(V)1.2, 1.6 and 1.7

Fiedler, B; Zhang, MM; Buczek, A; Azam, L; Bulaj, G; Norton, RS; Olivera, BM; Yoshikami, D

Author(s): Fiedler, B; Zhang, MM; Buczek, A; Azam, L; Bulaj, G; Norton, RS; Olivera, BM; Yoshikami, D;
Details: Publication Year 2008-06-15,Volume 75,Issue #12,Page 2334-2344
Journal Title: BIOCHEMICAL PHARMACOLOGY
Publication Type: Journal Article
Abstract: The excitotoxic conopeptide iota-RXIA induces repetitive action potentials in frog motor axons and seizures upon intracranial. injection into mice. We recently discovered that iota-RXIA shifts the voltage-dependence of activation of voltage-gated sodium channel Na(V)1.6 to a more hyperpolarized level. Here, we performed voltage-clamp experiments to examine its activity against rodent Na(V)1.1 through Na(V)1.7 co-expressed with the beta 1 subunit in Xenopus oocytes and Na(V)1.8 in dissociated mouse DRG neurons. The order of sensitivity to iota-RXIA was Na(V)1.6 > 1.2 > 1.7, and the remaining subtypes were insensitive. The time course Of iota-RXIA-activity on Na(V)1.6 during exposure to different peptide concentrations were well fit by single-exponential curves that provided k(obs). The Plot Of k(obs) versus [iota-RXIA] was linear, consistent with a bimolecular reaction with a K-d of similar to 3 mu M, close to the steady-state EC50 of similar to 2 mu M. iota-RXIA has an unusual residue, D-Phe, and the analog with an iota-Phe instead, iota-RXIA[L-Phe44], had a two-fold lower affinity and two-fold faster off-rate than iota-RXIA on Na(V)1.6 and furthermore was inactive on Na(V)1.2. iota-RXIA induced repetitive action potentials in mouse sciatic nerve with conduction velocities of both A- and C-fibers, consistent with the presence of Na(V)1.6 at nodes of Ranvier as well as in unmyelinated axons. Sixteen peptides homologous to iota-RXIA have been identified from a single species of Conus, so these peptides represent a rich family of novel sodium channel-targeting ligands. (C) 2008 Elsevier Inc. All rights reserved.
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Keywords: BETA-SCORPION TOXIN; D-AMINO-ACID; NERVOUS-SYSTEM; NA+ CHANNELS; ENHANCED ACTIVATION; FUNCTIONAL-ANALYSIS; DELTA-CONOTOXINS; MU-CONOTOXINS; CYSTINE KNOT; NEURONS
Publisher's Version: https://doi.org/10.1016/j.bcp.2008.03.019
Terms of Use/Rights Notice: Refer to copyright notice on published article.

Creation Date: 2008-06-15 12:00:00