Equinatoxin II : how a cationic pore-forming sea anemone toxin drives nodal swelling of myelinated nerve fibers

Benoit, Evelyne (author), Frangež, Robert (author), Ouanounou, Gilles (author), Meunier, Frédéric A. (author), Šuput, Dušan (author), Molgó, Jordi (author)

This study was performed to elucidate the mechanism underpinning the nodal swelling induced by equinatoxin II (EqtII), a cation-selective pore-forming toxin derived from the sea anemone Actinia equina. Experiments were conducted using frog myelinated nerve fibers as a model system. Application of EqtII led to an approximately two-fold increase in the nodal volume of myelinated axons, but only when extracellular Ca2+ was present. Replacing extracellular Cl− with isethionate had no measurable effect on this response, whereas substitution of NaCl with either sucrose or LiCl, an established Na+/Ca2+ exchanger (NCX) inhibitor, abolished the swelling. The persistence of the effect in the presence of tetrodotoxin indicates that voltage-gated Na+ channels are not involved in the underlying mechanism. Our data suggest that Ca2+ influx through EqtII-induced membrane pores raises intracellular Ca2+ levels, thereby stimulating the NCX in its forward-operating mode. This process promotes Ca2+ extrusion in exchange for Na+ entry. The resulting accumulation of intracellular Na+ increases osmotic pressure within the axon, leading to water influx and nodal swelling.

• Language: English
• Keywords: axonal swelling, cationic pore-forming peptide, confocal laser scanning microscopy, equinatoxin II, ionic mechanisms, myelinated nerve fiber
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: VF - Veterinary Faculty; MF - Faculty of Medicine
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 17 str.
• Numbering: Vol. 24, iss. 5, art. 187
• PID: 20.500.12556/RUL-182933
• UDC: 615.9:577.15:616.8
• ISSN on article: 1660-3397
• DOI: 10.3390/md24050187
• COBISS.SI-ID: 279259907
• Publication date in RUL: 29.05.2026

Record is a part of a journal

• Title: Marine drugs
• Shortened title: Mar. drugs
• Publisher: MDPI
• ISSN: 1660-3397
• COBISS.SI-ID: 23578841

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: otekanje aksonov, kationski peptid, ki tvori pore, konfokalna laserska vrstična mikroskopija, ekvinatoksin II, ionski mehanizmi, mielinizirano živčno vlakno