A mutation in the local anaesthetic binding site abolishes toluene effects in sodium channels.
Toluene is a solvent of abuse that inhibits cardiac sodium channels in a manner that resembles the action of local anaesthetics. The purpose of this work was to analyze toluene effects on skeletal muscle sodium channels with and without beta1 subunit (Nav1.4+beta1 and Nav1.4-beta1, respectively) expressed in Xenopus laevis oocytes and to compare them with those produced in the F1579A mutant channel lacking a local anaesthetic binding site. Toluene inhibited Nav1.4 sodium currents (IC50=2.7 mM in Nav1.4+beta1 and 2.2 mM in Nav1.4-beta1 in a concentration dependent way. Toluene (3 mM) blocked sodium currents in Nav1.4 channels proportionally throughout the entire current-voltage relationship producing inactivation at more negative potentials. Minimal inhibition was produced by 3 mM toluene in F1579A mutant channels. Recovery from inactivation was slower both in Nav1.4 and F1579A channels in the presence of 3 mM toluene. The solvent blocked sodium currents in a use-dependent and frequency-dependent manner in Nav1.4 channels. A single mutation in the local anaesthetic binding site of Nav1.4 channels almost abolished toluene effects. These results suggest that this site is important for toluene action.
Gauthereau
Marcia Y
MY
Departamento de Farmacobiología, Cinvestav. Calzada de los Tenorios #235, Col. Granjas Coapa, México, D.F. 14330, México.
Salinas-Stefanon
Eduardo M
EM
Cruz
Silvia L
SL
D000779:Anesthetics, Local / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D006801:Humans; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008012:Lidocaine / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009124:Muscle Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D009154:Mutation; D062553:NAV1.4 Voltage-Gated Sodium Channel; D009865:Oocytes; D012964:Sodium / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D012997:Solvents / Q000494:pharmacology*; D014050:Toluene / Q000494:pharmacology*; D014162:Transfection; D014982:Xenopus laevis
D000779:Anesthetics, Local; D009124:Muscle Proteins; D062553:NAV1.4 Voltage-Gated Sodium Channel; C106251:SCN4A protein, human; D015222:Sodium Channels; D012997:Solvents; D014050:Toluene; D008012:Lidocaine; D012964:Sodium