The effect of toxins fromAmeonia sulcata (Coelenterata) on neuromuscular transmission and nerve action potentials in the crayfish (Astacus leptodactylus)

Abstract

1. The effects of three toxins (ATX I, II and III) from the sea anemoneAnemonia sulcata have been investigated on neuromuscular transmission and nerve action potentials in the crayfisch. 2. In the neuromuscular preparations the toxins produce a gradual increase in the amplitude of the excitatory junction potentials until they reach the threshold for the generation of electrically excitable membrane responses. This is followed by repetitive activity of the motor axons, first on single stimuli, later occurring spontaneously. 3. The effects of the three toxins differ only with regard to the effective concentrations: threshold concentrations amount to 5×10−9 M for ATX I and II, to 10−7 M for ATX III. 4. The toxins show no postsynaptic effects on the muscle fibre membrane and on their electrical responses upon direct stimulation. 5. All toxins prolong the action potentials of the giant axons in the abdominal nerve cord. The duration may reach more than one second. The rate of rise of the action potentials is not affected. In several cases, however, an increase of the amplitude of the action potential was observed. 6. The effects of ATX I and II are irreversible in contrast to those of ATX III. 7. It is suggested that the high potency of the toxins in the nanomolar range, their small size, the known composition and, in the case of ATX II, sequence of amino acids together with the specificity of action on the sodium channels, proved in different preparations, make these substances to important tools in the study of excitable membranes.