Tetrodotoxin (TTX) is the poison that makes puffer fish so dangerous to eat. Tetrodotoxin causes paralysis by selectively blocking sodium ion channels in the membranes of excitable cells (that is - neurons). As a result, nerve impulses cannot propagate and death is inevitable.

Tetrodotoxin binds tightly and physically blocks the channel, preventing sodium currents from passing through the membrane. Only 100 molecules of toxin will completely deplete activity of a one square micron of tissue. Tetrodotoxin is also used in neurophysiological experiments to study the role of sodium channels in nerve behavior.

See also: neurotoxin