Competitive binding interaction between Zn2+ and saxitoxin in cardiac Na+ channels. Evidence for a sulfhydryl group in the Zn2+/saxitoxin binding site

Détails

ID Serval
serval:BIB_6684E4C83757
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
Competitive binding interaction between Zn2+ and saxitoxin in cardiac Na+ channels. Evidence for a sulfhydryl group in the Zn2+/saxitoxin binding site
Périodique
Biophysical Journal
Auteur(s)
Schild  L., Moczydlowski  E.
ISSN
0006-3495 (Print)
Statut éditorial
Publié
Date de publication
03/1991
Volume
59
Numéro
3
Pages
523-37
Notes
In Vitro
Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S. --- Old month value: Mar
Résumé
Mammalian heart Na+ channels exhibit approximately 100-fold higher affinity for block by external Zn2+ than other Na+ channel subtypes. With batrachotoxin-modified Na+ channels from dog or calf heart, micromolar concentrations of external Zn2+ result in a flickering block to a substate level with a conductance of approximately 12% of the open channel at -50 mV. We examined the hypothesis that, in this blocking mode, Zn2+ binds to a subsite of the saxitoxin (STX) binding site of heart Na+ channels by single-channel analysis of the interaction between Zn2+ and STX and also by chemical modification experiments on single heart Na+ channels incorporated into planar lipid bilayers in the presence of batrachotoxin. We found that external Zn2+ relieved block by STX in a strictly competitive fashion. Kinetic analysis of this phenomenon was consistent with a scheme involving direct binding competition between Zn2+ and STX at a single site with intrinsic equilibrium dissociation constants of 30 nM for STX and 30 microM for Zn2+. Because high-affinity Zn2(+)-binding sites often include sulfhydryl groups as coordinating ligands of this metal ion, we tested the effect of a sulfhydryl-specific alkylating reagent, iodoacetamide (IAA), on Zn2+ and STX block. For six calf heart Na+ channels, we observed that exposure to 5 mM IAA completely abolished Zn2+ block and concomitantly modified STX binding with at least 20-fold reduction in affinity. These results lead us to propose a model in which Zn2+ binds to a subsite within or near the STX binding site of heart Na+ channels. This site is also presumed to contain one or more cysteine sulfhydryl groups.
Mots-clé
Amino Acid Sequence Animals Binding, Competitive Biophysics Cattle Dogs Iodoacetamide/pharmacology Kinetics Molecular Sequence Data Myocardium/*metabolism Saxitoxin/metabolism Sodium Channels/drug effects/genetics/*metabolism Zinc/metabolism
Pubmed
Web of science
Open Access
Oui
Création de la notice
24/01/2008 13:56
Dernière modification de la notice
20/08/2019 15:22
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