The neurotoxic action of toxin gamma from the
venom of the Brazilian scorpion Tityus serrulatus (
TiTx gamma) has been investigated in cultured mouse
neuroblastoma cells (N1E115) using the suction pipette technique. Addition of 14 to 53 nM
TiTx gamma to the external
solution causes nerve cell membrane depolarization, membrane potential oscillations and spontaneous action potentials within 10 min. None of these effects were observed within 15 min after application of 1 microM toxin IV from Centruroides sculpturatus
venom. Under voltage clamp the amplitude of the
sodium current evoked by test pulses to potentials more positive than -30 mV is reversibly reduced by 50% after 17 to 105 nM
TiTx gamma. On the other hand, a
sodium current component appears after
TiTx gamma at test pulse potentials between -70 and -40 mV, for which no
sodium current is observed in the control experiment. The outward
potassium current is not significantly affected by the highest
TiTx gamma concentrations used. The potential-dependence of inactivation of the
sodium current component that is induced by
TiTx gamma is shifted by -30 mV with respect to control values. The local anaesthetic procain at 1 mM discriminates between the two populations of
sodium channels observed in the presence of
TiTx gamma.