Purified ciguatoxin-induced modifications in excitability of myelinated nerve fibre.

The effects of external applications of 0.22-1.12 nM of purified ciguatoxin (CTX-1B), extracted from the moray-eel, were studied on frog current and voltage clamped node of Ranvier. CTX-1B induced spontaneous action potentials at a frequency of 70-100 Hz, suppressed by 50 microM lidocaine, which resulted from a toxin-induced maintained (late) inward Na current representing about 5.5% of peak Na current. Peak and late currents showed different voltage characteristics but were similarly affected by 50-500 microM lidocaine. It is concluded that the effects of CTX-1B are qualitatively but not quantitatively similar to those previously studied of partially purified toxin (2).