RESUMEN
The effect of the venom of the spider Lycosa erythrognatha on the frog sciatic nerve was investigated with the single sucrose-gap method. Solutions containing the crude venom (40 µg protein/ml) markedly increased the duration of compound action potentials and caused the appearance of long-lasting depolarizing post-potentials. These effects were only partially (20 percent) reversded by extensive washsing with control solution. The active material was sensitive to proteolytic treatments with pronase or trypsin and was separated with 20 percent acetonitrile and 0.1 percent trifluoroacetic acid by reverse phase chromatography. The effect of this fraction (LycIV) on the post-potential amplitude was concentration-dependent, and was fitted with a quadratic hyperbola having a half maximal effect of 0.9 µg protein/ml. SDS-polyacrylamide gel electrophoresis of LycIV showed an enriched polypeptide band with apparent molecular weight of ~8 kDa. The observed effects were similar to those of toxins that inhibit sodium channel inactivation and different from the effects of potassium channel blockers. Pore formation or membrane disruption could be ruled out. It was concluded that the venom contains a neurotoxic polypeptide that alters the repolarization of action potentials, probably by inhibiting sodium channel inactivation