Abstract: Assay for identifying an inactivation gate inhibitor of a sodium channel, by: establishing first and a second cultures of cells having a wild-type sodium channel and third and a fourth cultures of cells having a noninactivating mutant sodium channel; measuring a baseline sodium current for one or more cells in the first and the second cultures, and a baseline inactivation rate for one or more cells in the third and the fourth cultures; treating the cells in the first and the third cultures with either a candidate inhibitor or an IFM amide control, and the cells in the second and the fourth cultures with an inactive control peptide; measuring a test sodium current in one or more cells in the first and the second cultures, and a test inactivation rate in one or more cells in the third and the fourth cultures; and determining that the candidate inhibitor is an inactivation gate inhibitor of the sodium channel if the test sodium current of the cells in the first culture is lower than the baseline of the first cul