Trans-Channel Interactions in Batrachotoxin-Modified Rat Skeletal Muscle Sodium Channels: Kinetic Analysis of Mutual Inhibition between μ-Conotoxin GIIIA Derivatives and Amine Blockers
| Autor: | Evgeny Pavlov, Gerald W. Zamponi, Tatiana Britvina, Quanli Ma, Robert J. French |
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| Rok vydání: | 2008 |
| Předmět: |
Stereochemistry
Kinetics Biophysics Ligands Binding Competitive Sodium Channels 03 medical and health sciences chemistry.chemical_compound 0302 clinical medicine Animals Channels Receptors and Electrical Signaling Conotoxin Amines Batrachotoxins Muscle Skeletal 030304 developmental biology 0303 health sciences Sodium channel Rats Quaternary Ammonium Compounds Dissociation constant Membrane chemistry Batrachotoxin Amine gas treating Steady state (chemistry) Conotoxins 030217 neurology & neurosurgery Protein Binding Sodium Channel Blockers |
| Zdroj: | Biophysical Journal. 95:4266-4276 |
| ISSN: | 0006-3495 |
| DOI: | 10.1529/biophysj.108.138271 |
| Popis: | R13X derivatives of mu-conotoxin GIIIA bind externally to single sodium channels and block current incompletely with mean "blocked" durations of several seconds. We studied interactions between two classes of blockers (mu-conotoxins and amines) by steady state, kinetic analysis of block of BTX-modified Na channels in planar bilayers. The amines cause all-or-none block at a site internal to the selectivity filter. TPrA and DEA block single Na channels with very different kinetics. TPrA induces discrete, all-or-none, blocked events (mean blocked durations, approximately 100 ms), whereas DEA produces a concentration-dependent reduction of the apparent single channel amplitude ("fast" block). These distinct modes of action allow simultaneous evaluation of block by TPrA and DEA, showing a classical, competitive interaction between them. The apparent affinity of TPrA decreases with increasing [DEA], based on a decrease in the association rate for TPrA. When an R13X mu-conotoxin derivative and one of the amines are applied simultaneously on opposite sides of the membrane, a mutually inhibitory interaction is observed. Dissociation constants, at +50 mV, for TPrA ( approximately 4 mM) and DEA ( approximately 30 mM) increase by approximately 20%-50% when R13E (nominal net charge, +4) or R13Q (+5) is bound. Analysis of the slow blocking kinetics for the two toxin derivatives showed comparable decreases in affinity of the mu-conotoxins in the presence of an amine. Although this mutual inhibition seems to be qualitatively consistent with an electrostatic interaction across the selectivity filter, quantitative considerations raise questions about the mechanistic details of the interaction. |
| Databáze: | OpenAIRE |
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