Objective The effects ofANEPⅢ,a novel recombinant neurotoxic polypeptide originally from Buthus martensi Karsch,on sodium currents were studied in primary cultured rat hippocampal and neocortical neurons.Methods sodium currents were studied using the whole-cell patch clamp recording techniques.Results 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 neocortical neurons revealed an IC50 value of 214.76 nmol/L and 124.57 nmol/L at a potential of-30 mV and-20 mV,respectively.For the different types of neurons,the shift of the current-voltage relation was distinct and was 9.7 mV in hippocampal neurons,and 5.7 mV in neocortical cells with 1000 nmol/L ANEPⅢ.Furthermore,the time constant for recovery from inactivation was also prolonged by 1000 nmol/L ANEPⅢ.Conclusion Taken together,our results demonstrated that ANEPⅢ in submicromolar concentration was a voltage-dependent,reversible blocker of sodium currents in hippocampal and neocortical neurons,which,at least in part,contributed to the anti-neuroexcitatory properties of this peptide.