On the structural basis for size-selective permeation of organic cations through the voltage-gated sodium channel. Effect of alanine mutations at the DEKA locus on selectivity, inhibition by Ca2+ and H+, and molecular sieving

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ID Serval
serval:BIB_628E54AF0234
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
On the structural basis for size-selective permeation of organic cations through the voltage-gated sodium channel. Effect of alanine mutations at the DEKA locus on selectivity, inhibition by Ca2+ and H+, and molecular sieving
Périodique
Journal of General Physiology
Auteur(s)
Sun  Y. M., Favre  I., Schild  L., Moczydlowski  E.
ISSN
0022-1295 (Print)
Statut éditorial
Publié
Date de publication
12/1997
Volume
110
Numéro
6
Pages
693-715
Notes
Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S. --- Old month value: Dec
Résumé
Recent evidence indicates that ionic selectivity in voltage-gated Na+ channels is mediated by a small number of residues in P-region segments that link transmembrane elements S5 and S6 in each of four homologous domains denoted I, II, III, and IV. Important determinants for this function appear to be a set of conserved charged residues in the first three homologous domains, Asp(I), Glu(II), and Lys(III), located in a region of the pore called the DEKA locus. In this study, we examined several Ala-substitution mutations of these residues for alterations in ionic selectivity, inhibition of macroscopic current by external Ca2+ and H+, and molecular sieving behavior using a series of organic cations ranging in size from ammonium to tetraethylammonium. Whole-cell recording of wild-type and mutant channels of the rat muscle micro1 Na+ channel stably expressed in HEK293 cells was used to compare macroscopic current-voltage behavior in the presence of various external cations and an intracellular reference solution containing Cs+ and very low Ca2+. In particular, we tested the hypothesis that the Lys residue in domain III of the DEKA locus is responsible for restricting the permeation of large organic cations. Mutation of Lys(III) to Ala largely eliminated selectivity among the group IA monovalent alkali cations (Li+, Na+, K+, Rb+, Cs+) and permitted inward current of group IIA divalent cations (Mg2+, Ca2+, Sr2+, Ba2+). This same mutation also resulted in the acquisition of permeability to many large organic cations such as methylammonium, tetramethylammonium, and tetraethylammonium, all of which are impermeant in the native channel. The results lead to the conclusion that charged residues of the DEKA locus play an important role in molecular sieving behavior of the Na+ channel pore, a function that has been previously attributed to a hypothetical region of the channel called the "selectivity filter." A detailed examination of individual contributions of the Asp(I), Glu(II), and Lys(III) residues and the dependence on molecular size suggests that relative permeability of organic cations is a complex function of the size, charge, and polarity of these residues and cation substrates. As judged by effects on macroscopic conductance, charged residues of the DEKA locus also appear to play a role in the mechanisms of block by external Ca2+ and H+, but are not essential for the positive shift in activation voltage that is produced by these ions.
Mots-clé
Alanine/*genetics Alkalies/metabolism Calcium/*pharmacology Cations, Divalent/metabolism/*pharmacology Cells, Cultured *Conotoxins Electric Stimulation Humans Ion Channel Gating/drug effects/*physiology Kidney/cytology Molecular Weight Mutagenesis, Site-Directed/physiology Patch-Clamp Techniques Peptides, Cyclic/pharmacology Protons Saxitoxin/pharmacology Sensitivity and Specificity Sodium Channels/*chemistry/genetics Tetrodotoxin/pharmacology
Pubmed
Web of science
Open Access
Oui
Création de la notice
24/01/2008 12:55
Dernière modification de la notice
20/08/2019 14:19
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