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Article: Dependence of μ-conotoxin block of sodium channels on ionic strength but not on the permeating [Na+]. Implications for the distinctive mechanistic interactions between Na+ and K+ channel pore-blocking toxins and their molecular targets

TitleDependence of μ-conotoxin block of sodium channels on ionic strength but not on the permeating [Na+]. Implications for the distinctive mechanistic interactions between Na+ and K+ channel pore-blocking toxins and their molecular targets
Authors
KeywordsSpecies Index: Animalia
Conus Geographus
Gastropoda
Liparis (Scorpaeniform)
Issue Date2003
PublisherAmerican Society for Biochemistry and Molecular Biology, Inc. The Journal's web site is located at http://www.jbc.org/
Citation
Journal Of Biological Chemistry, 2003, v. 278 n. 33, p. 30912-30919 How to Cite?
Abstractμ-Conotoxins (μ-CTXs) are Na+ channel-blocking, 22-amino acid peptides produced by the sea snail Conus geographus. Although K+ channel pore-blocking toxins show specific interactions with permeant ions and strong dependence on the ionic strength (μ), no such dependence has been reported for μ-CTX and Na+ channels. Such properties would offer insight into the binding and blocking mechanism of μ-CTX as well as functional and structural properties of the Na+ channel pore. Here we studied the effects of μ and permeant ion concentration ([Na+]) on μ-CTX block of rat skeletal muscle (μ1, Nav1.4) Na + channels. μ-CTX sensitivity of wild-type and E758Q channels increased significantly (by ∼20-fold) when μ was lowered by substituting external Na+ with equimolar sucrose (from 140 to 35 mM Na +); however, toxin block was unaltered (p > 0.05) when μ was maintained by replacement of [Na+] with N-methyl-D-glucamine (NMG+), suggesting that the enhanced sensitivity at low μ was not due to reduction in [Na+]. Single-channel recordings identified the association rate constant, kon, as the primary determinant of the changes in affinity (kon increased 40- and 333-fold for μ-CTX D2N/R13Q and D12N/R13Q, respectively, when symmetric 200 mM Na+ was reduced to 50 mM). In contrast, dissociation rates changed <2-fold for the same derivatives under the same conditions. Experiments with additional μ-CTX derivatives identified toxin residues Arg-1, Arg-13, and Lys-16 as important contributors to the sensitivity to external μ. Taken together, our findings indicate that μ-CTX block of Na+ channels depends critically on μ but not specifically on [Na+], contrasting with the known behavior of pore-blocking K+ channel toxins. These findings suggest that different degrees of ion interaction, underlying the fundamental conduction mechanisms of Na+ and K+ channels, are mirrored in ion interactions with pore-blocking toxins.
Persistent Identifierhttp://hdl.handle.net/10722/91639
ISSN
2015 Impact Factor: 4.258
2015 SCImago Journal Rankings: 3.151
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorLi, RAen_HK
dc.contributor.authorHui, Ken_HK
dc.contributor.authorFrench, RJen_HK
dc.contributor.authorSato, Ken_HK
dc.contributor.authorHenrikson, CAen_HK
dc.contributor.authorTomaselli, GFen_HK
dc.contributor.authorMarbán, Een_HK
dc.date.accessioned2010-09-17T10:22:37Z-
dc.date.available2010-09-17T10:22:37Z-
dc.date.issued2003en_HK
dc.identifier.citationJournal Of Biological Chemistry, 2003, v. 278 n. 33, p. 30912-30919en_HK
dc.identifier.issn0021-9258en_HK
dc.identifier.urihttp://hdl.handle.net/10722/91639-
dc.description.abstractμ-Conotoxins (μ-CTXs) are Na+ channel-blocking, 22-amino acid peptides produced by the sea snail Conus geographus. Although K+ channel pore-blocking toxins show specific interactions with permeant ions and strong dependence on the ionic strength (μ), no such dependence has been reported for μ-CTX and Na+ channels. Such properties would offer insight into the binding and blocking mechanism of μ-CTX as well as functional and structural properties of the Na+ channel pore. Here we studied the effects of μ and permeant ion concentration ([Na+]) on μ-CTX block of rat skeletal muscle (μ1, Nav1.4) Na + channels. μ-CTX sensitivity of wild-type and E758Q channels increased significantly (by ∼20-fold) when μ was lowered by substituting external Na+ with equimolar sucrose (from 140 to 35 mM Na +); however, toxin block was unaltered (p > 0.05) when μ was maintained by replacement of [Na+] with N-methyl-D-glucamine (NMG+), suggesting that the enhanced sensitivity at low μ was not due to reduction in [Na+]. Single-channel recordings identified the association rate constant, kon, as the primary determinant of the changes in affinity (kon increased 40- and 333-fold for μ-CTX D2N/R13Q and D12N/R13Q, respectively, when symmetric 200 mM Na+ was reduced to 50 mM). In contrast, dissociation rates changed <2-fold for the same derivatives under the same conditions. Experiments with additional μ-CTX derivatives identified toxin residues Arg-1, Arg-13, and Lys-16 as important contributors to the sensitivity to external μ. Taken together, our findings indicate that μ-CTX block of Na+ channels depends critically on μ but not specifically on [Na+], contrasting with the known behavior of pore-blocking K+ channel toxins. These findings suggest that different degrees of ion interaction, underlying the fundamental conduction mechanisms of Na+ and K+ channels, are mirrored in ion interactions with pore-blocking toxins.en_HK
dc.languageengen_HK
dc.publisherAmerican Society for Biochemistry and Molecular Biology, Inc. The Journal's web site is located at http://www.jbc.org/en_HK
dc.relation.ispartofJournal of Biological Chemistryen_HK
dc.subjectSpecies Index: Animaliaen_HK
dc.subjectConus Geographusen_HK
dc.subjectGastropodaen_HK
dc.subjectLiparis (Scorpaeniform)en_HK
dc.subject.meshAnimalsen_HK
dc.subject.meshArginine - geneticsen_HK
dc.subject.meshCalcium Channel Blockers - pharmacologyen_HK
dc.subject.meshConotoxins - pharmacologyen_HK
dc.subject.meshGlutamic Acid - geneticsen_HK
dc.subject.meshIon Channel Gating - drug effectsen_HK
dc.subject.meshLysine - geneticsen_HK
dc.subject.meshMembrane Potentials - drug effectsen_HK
dc.subject.meshMuscle, Skeletal - metabolismen_HK
dc.subject.meshMutagenesis, Site-Directeden_HK
dc.subject.meshProtein Structure, Tertiaryen_HK
dc.subject.meshRatsen_HK
dc.subject.meshSodium - pharmacokineticsen_HK
dc.subject.meshSodium Channel Blockers - pharmacologyen_HK
dc.subject.meshSodium Channels - chemistry - genetics - metabolismen_HK
dc.titleDependence of μ-conotoxin block of sodium channels on ionic strength but not on the permeating [Na+]. Implications for the distinctive mechanistic interactions between Na+ and K+ channel pore-blocking toxins and their molecular targetsen_HK
dc.typeArticleen_HK
dc.identifier.emailLi, RA:ronaldli@hkucc.hku.hken_HK
dc.identifier.authorityLi, RA=rp01352en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1074/jbc.M301039200en_HK
dc.identifier.pmid12764145en_HK
dc.identifier.scopuseid_2-s2.0-0042009353en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-0042009353&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume278en_HK
dc.identifier.issue33en_HK
dc.identifier.spage30912en_HK
dc.identifier.epage30919en_HK
dc.identifier.isiWOS:000184658800064-
dc.publisher.placeUnited Statesen_HK
dc.identifier.scopusauthoridLi, RA=7404724466en_HK
dc.identifier.scopusauthoridHui, K=9248852500en_HK
dc.identifier.scopusauthoridFrench, RJ=7202789440en_HK
dc.identifier.scopusauthoridSato, K=7406409211en_HK
dc.identifier.scopusauthoridHenrikson, CA=7004279066en_HK
dc.identifier.scopusauthoridTomaselli, GF=7005223451en_HK
dc.identifier.scopusauthoridMarbán, E=8075977300en_HK
dc.identifier.citeulike9671507-

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