Sea anemone toxin:a tool to study molecular mechanisms of nerve conduction and excitation-secretion coupling

The effects of polypeptide neurotoxin from Anemonia sulcata on nerve conduction in crayfish giant axons and on frog myelinated fibers have been analyzed. The main features of toxin action are the following: (i) the toxin acts at very low doses and its action is apparently irreversible. (ii) The toxin selectively affects the closing (inactivation) of the Na+ channel by slowing it down considerably; it does not alter the opening mechanism of the Na+ channel or the steady-state potassium conductance. (iii) The tetrodotoxin-receptor association is unaffected by previous treatment of the axonal membrane with the sea anemone toxin. (iv) Conversely, the sea anemone toxin can only associate with the membrane when the Na+ channel is open for Na+; it does not bind when the channel is previously blocked by tetrodotoxin. (v) Besides its effect on the action potential, the sea anemone toxin displays a veratridine-type depolarizing action at low Ca2+ concentration which can be suppressed by tetrodotoxin. The sea anemone toxin greatly stimulates the release of gamma-[3H]aminobutyric acid from neurotransmitter-loaded rat brain synaptosomes. The apparent dissociation constant of the neurotoxin-receptor complex in this system is 20 nM. The sea anemone toxin effect is antagonized by tetrodotoxin.