Tetrodotoxin, Saxitoxin and Veratridine

Neurotoxins can act by blocking gates in the axonal membrane in closed or open states.

Tetrodotoxin is found in some organs of the puffer fish. TTX binds specifically to the Na+ channel, blocking all ion movement.

Saxitoxin is contained in the marine dinoflagellates responsible for “red tide” also block Na+ channels.

Veratridine is found in the seeds of a plant of the lily family, Schoenocaulon officinale. This toxin also binds to the Na+ channels but blocks them in the “open” configuration.

These toxins have proven to be useful in studies of axonal structure and conduction, for their tight binding makes them excellent affinity labels for the channel.