Lowering of the coronary flow in isolated rat heart by equinatoxin II depends upon extracellular Ca2+ concentration

Equinatoxin II (EqT II) is a basic polypeptide toxin from the sea anemone A ctinia equina (L.). Its LD50 in mice is 33 g/kg. The cause of death after i ntravenous application has been attributed to the circulatory failure resul ting in the cardiotoxic effects. In Langendorff's rat and guinea-pig heart preparations EqT II caused dose dependent decrease in the coronary flow (CF ) Morphologic changes of different cell cultures incubated with EqT II are the result of Ca2+ entry through the newly formed discrete pores. Pores in the cell membranes are; composed of the toxin oligomeres. In the present st udy we tried to evaluate the dependence of vasoconstrictor effects of EqT I I on isolated rat hearts upon the Ca2+ concentration in the perfusion solut ion. EqT II did not affect the CF in the group without Ca2+. The strongest effect was observed in the group with 1.5 mM Ca2+ where the CF decreased to 7.7+/-7%. The results of our experiments indicate that the effects of EqT II on CP depend on Ca2+ concentration in the extracellular solution.