Effect of ANEPIII, a novel recombinant neurotoxic polypeptide, on sodium channels in primary cultured rat hippocampal and cortical neurons.

Previous studies have shown that the recombinant neurotoxic polypeptide BmK ANEP (ANEPIII) displayed good anti-neuroexcitation activity as demonstrated by pharmacological tests of the blockade of chemical-induced convulsive seizures. In order to search for further anticonvulsant mechanism of action of ANEPIII, the effects of ANEPIII on sodium channels were assessed using the whole-cell patch clamp recordings in primary cultures of rat hippocampal and cortical neurons. ANEPIII decreased the sodium currents in a voltage-dependent manner, which appeared as a shift of the current-voltage relation to positive potentials. The effect was reversible after washing. The concentration-responsiveness measured in hippocampal and cortical neurons revealed an IC(50) value of 124.6 nM and 192.7 nM, respectively. Furthermore, ANEPIII 1000 nM significantly shifted the activation curves of sodium current in hippocampal and cortical neurons to more positive potentials and the recovery from inactivation of sodium current was significantly slower. Voltage-dependent inactivation curves of sodium channels in hippocampal and cortical neurons did not change in the presence of 1000 nM ANEPIII. Thus, our results demonstrated that ANEPIII in submicromolar concentrations was a voltage-dependent, reversible blocker of sodium current in hippocampal and cortical neurons. It is concluded that these phenomena may explain, at least in part, the anti-neuroexciting properties of this peptide.