Tetrodotoxin does not block excitation from inside the nerve membrane.
Tetrodotoxin does not block the action potential or membrane sodium current when internally perfused through the giant axon of a squid at much higher concentrations than those required for blocking by external application. It is suggested that the gate for the sodium channel is located on the exterior surface of the axon, because tetrodotoxin is not lipid soluble.
D000818:Animals; D001369:Axons / Q000187:drug effects*; D004594:Electrophysiology; D066298:In Vitro Techniques; D008974:Mollusca; D009431:Neural Conduction / Q000187:drug effects*; D011188:Potassium; D012964:Sodium; D013779:Tetrodotoxin / Q000494:pharmacology; D014118:Toxins, Biological / Q000494:pharmacology*
D014118:Toxins, Biological; D013779:Tetrodotoxin; D012964:Sodium; D011188:Potassium