Ciguatoxin is a novel of type of Na⁺ channel toxin

Purified ciguatoxin at 0.1 to 10 ng/ml inhibits the net accumulation of neurotransmitters (y-aminobutyric acid and dopamine) by brain synaptosomes. This action is due to a stimulation of neurotransmitter release.
The half-maximum effect of the toxinis observed at 0.62 ng/ml. The effect of ciguatoxin is completely inhibited by tetrodotoxin = 4 nM). Electrophysiological
studies on neuroblastoma cells indicate that ciguatoxin induces a membrane depolarization which is prevented by tetrodotoxin and which is due to an
action that increases Na⁺ permeability. Under appropriate conditions ciguatoxicnr eates spontaneous oscillations in the membrane polarization level and repeated
action potentials. Ciguatoxin stimulates ²²Na⁺ entry through the voltage-dependent Na⁺ channels of neuroblastoma cells and rat skeletal myoblasts when it is used in synergy with veratridine, batrachotoxin, pyrethroids, sea anemone, or scorpion toxins. The half-maximum effect of ciguatoxin on ²²Na⁺ flux in the
presence of veratridine occurs at a concentration of 0.5 ng/ml. Stimulation of ²²Na⁺ flux by ciguatoxin is abolished by tetrodotoxin. These results taken together indicate that ciguatoxin belongs to a new class of toxins acting on Na⁺ channels.