Effects of equinatoxin II on isolated guinea pig taenia caeci muscle contractility and intracellular Ca super(2) super(+)

• Published in: Toxicon (Oxford) Vol. 51; no. 8; pp. 1416 - 1423
• Main Authors: Frangez, R, Suput, D, Molgo, J
• Format: Journal Article
• Language: English
• Published: 15.06.2008
• Subjects: Actinia equina
• ISSN: 0041-0101
• DOI: 10.1016/j.toxicon.2008.03.013

Equinatoxin II (EqT II) is a ~20kDa cytotoxic and cytolytic protein isolated from the sea anemone Actinia equina. When injected intravenously to rats the toxin has been reported to produce a rapid cardiorespiratory arrest. In the present study, we show that EqT II increases the tension of spontaneous contractions and induces long-lasting contracture of guinea pig taenia caeci muscle. In taenia caeci, dissociated smooth muscle cells, microspectrofluorometric measurements, using the Ca super(2) super(+) indicator fura-2/AM, revealed that the toxin causes a marked increase in intracellular calcium, provided Ca super(2) super(+) is present in the external medium. The increase in intracellular Ca super(2) super(+) by EqT II was not blocked or diminished by the calcium channel blocker verapamil. Furthermore, pre-treatment of smooth muscle cells with Ca super(2) super(+)-ATPase inhibitor thapsigargin, or exposure of the cells to a high K super(+) (75mM) medium did not prevent EqT II-induced intracellular Ca super(2) super(+) increases. Replacement of external sodium by sucrose markedly modified the time course of Ca super(2) super(+) signals suggesting the involvement of the Na super(+)/Ca super(2) super(+) exchanger in EqT II action. Our results strongly suggest that EqT II-induced increase in intracellular Ca super(2) super(+) and muscle tension are both dependent on the ability of EqT II to insert into the membrane and form pores allowing Ca super(2) super(+) influx into the cells. To our knowledge this is the first report showing that EqT II causes contraction and contracture of taenia caeci muscles and increases intracellular Ca super(2) super(+) in smooth muscle cells.