Equinatoxin II increases intracellular Ca²⁺ in NG 108-15 cells

Equinatoxin II (EqT II) is a basic 20 kD protein isolated from the sea anemone Actinia equina. Intravenous injection of 3 LD₅₀ of EqT II causes cardiorespiratory arrest. The aim of our study was to check the effects of EqT II on neuronal cells to assess the role of neuronal mechanisms in respiratory arrest after intravenous injection of the toxin. Effects of EqT II on mouse neuroblastoma x rat glioma NG108-15 cell were studied using confocal laser scanning microscopy and by Fura-2 fluorescence measurements. The results show that EqT II applied in nanomolar range increases intracellular Ca²⁺ activity significantly, which is possibly responsible for the morphological changes of NG108-15 cells after the exposure to 10 nM EqT II. Intracellular increase in Ca²⁺ activity can not be prevented by use of the various pharmacological substances (e.g. Ca²⁺ channels blocker Verapamil and Bekanamycin). Swelling of the NG108-15 cells after the exposure to the EqT II also can not be blocked with the sodium channel blocker tetrodotoxin. Increase in the intracellular Ca²⁺ activity is probably a result of Ca²⁺ entry through pores produced by the toxin, which has been shown by other authors on other cells and on phospholipid bilayer. Respiratory arrest after intravenous injection of the toxin can be caused by the action of the toxin on neuronal cells in medulla oblongata provided that EqT II can damage blood brain barrier thus enabling access to the neuronal cells. The results allow the conclusion that EqT II can affect normal calcium homeostasis and cell morphology of neuronal cells that can disturb cell physiology and its function thus affecting normal respiratory pattern.