Biological significance of peptides from Anemonia sulcata

Three polypeptide toxins have been isolated from the sea anemone Anemonia sulcata and characterized: ATX I (mol wt 4702), ATX II (mol wt 4935), and ATX II (mol wt 2678). In different crustacean and amphibian preparations the toxins act primarily on the fast sodium channels, which leads to delayed inactivation of fast sodium permeability and thus increases the duration of the action potential. When applied to crustacean preparations the three toxins are nearly equally effective. However, in a comparison of the biological activities of ATX I and ATX II in myelinated nerves of the frog, ATX I seems to be inactive. It is suggested that cardiotoxicity is the primary cause of death in mammals, ATX II being more toxic than ATX I. At very low concentrations ATX II induces a pronounced positive inotropic effect in different mammalian heart preparations, which is accompanied by a prolongation of the action potential. It is suggested that the positive inotropic effect of ATX II is caused by a delayed inactivation of the fast sodium current, which leads to an increase of the sodium transient and of the pump activity of Na+,K+-ATPase. In contrast to the presynaptic mode of action on crustacean and frog nerve-muscle preparations, ATX II has a direct effect on mammalian skeletal muscle fiber membranes and induces a sodium-dependent increase of twitch responses and duration of the action potential.