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

Equinatoxin II (EqT II) isa basic 20 kD protein isolated from the sea anemo ne Actinia equina. Intravenous injection of 3 LD50 of EqT II causes cardior espiratory arrest. The aim of our study was to check the effects of EqT IT 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 s how that EqT II applied in nanomolar range increases intracellular Ca2+ act ivity significantly, which is possibly responsible for the morphological ch anges of NG108-15 cells after the exposure to 10 nM EqT II. Intracellular i ncrease in Ca2+ activity can not be prevented by use of the various pharmac ological substances (e.g. Ca2+ channels blocker Verapamil and Bekanamycin). Swelling of the NG108-15 cells after the exposure to the EqT II also can n ot be blocked with the sodium channel blocker tetrodotoxin. Increase in the intracellular Ca2+ activity is probably a result of Ca2+ entry through por es produced by the toxin, which has been shown by other authors on other ce lls and on phospholipid bilayer. Respiratory arrest after intravenous injec tion of the toxin can be caused by the action of the toxin on neuronal cell s in medulla oblongata provided that EqT II can damage blood brain barrier thus enabling access to the neuronal cells. The results allow the conclusio n that EqT II can affect normal calcium homeostasis and cell morphology of neuronal cells that can disturb cell physiology and its function thus affec ting normal respiratory pattern.