A delta-conotoxin from Conus ermineus venom inhibits inactivation in vertebrate neuronal Na+ channels but not in skeletal and cardiac muscles.
We have isolated delta-conotoxin EVIA (delta-EVIA), a conopeptide in Conus ermineus venom that contains 32 amino acid residues and a six-cysteine/four-loop framework similar to that of previously described omega-, delta-, microO-, and kappa-conotoxins. However, it displays low sequence homology with the latter conotoxins. delta-EVIA inhibits Na+ channel inactivation with unique tissue specificity upon binding to receptor site 6 of neuronal Na+ channels. Using amphibian myelinated axons and spinal neurons, we showed that delta-EVIA increases the duration of action potentials by inhibiting Na+ channel inactivation. delta-EVIA considerably enhanced nerve terminal excitability and synaptic efficacy at the frog neuromuscular junction but did not affect directly elicited muscle action potentials. The neuronally selective property of delta-EVIA was confirmed by showing that a fluorescent derivative of delta-EVIA labeled motor nerve endings but not skeletal muscle fibers. In a heterologous expression system, delta-EVIA inhibited inactivation of rat neuronal Na+ channel subtypes (rNaV1.2a, rNaV1.3, and rNaV1.6) but did not affect rat skeletal (rNaV1.4) and human cardiac muscle (hNaV1.5) Na+ channel subtypes. delta-EVIA, in the range of concentrations used, is the first conotoxin found to affect neuronal Na+ channels without acting on Na+ channels of skeletal and cardiac muscle. Therefore, it is a unique tool for discriminating voltage-sensitive Na+ channel subtypes and for studying the distribution and modulation mechanisms of neuronal Na+ channels, and it may serve as a lead to design new drugs adapted to treat diseases characterized by defective nerve conduction.
Barbier
Julien
J
Laboratoire de Neurobiologie Cellulaire et Moléculaire, UPR 9040, CNRS, 91198 Gif-sur-Yvette cedex, France.
Lamthanh
Hung
H
Le Gall
Frédéric
F
Favreau
Philippe
P
Benoit
Evelyne
E
Chen
Haijun
H
Gilles
Nicolas
N
Ilan
Nitza
N
Heinemann
Stefan H
SH
Gordon
Dalia
D
Ménez
André
A
Molgó
Jordi
J
D000200:Action Potentials / Q000187:drug effects; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D020916:Conotoxins / Q000235:genetics / Q000302:isolation & purification / Q000494:pharmacology*; D003532:Cyprinodontiformes; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D011893:Rana esculenta; D051381:Rats; D011994:Recombinant Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015222:Sodium Channels / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D014981:Xenopus
D020916:Conotoxins; D011994:Recombinant Proteins; D015222:Sodium Channels; C108141:conotoxin EIVA