Cell bioassay of neurotoxins

A cell bioassay is provided for determining the presence in a fluid sample of a sodium channel-activating toxin wherein (a) a fluid sample is incubated in the presence of a culture of cells which express voltage-gated sodium channels and which are responsive in a dose-dependent manner to sodium channel-activating toxins and a medium comprising an agent which causes persistent activation of the voltage-gated sodium channel; (b) the culture is incubated with a medium comprising an indicator which is acted upon by living cells to generate a discernable result, (c) the culture is observed for an incidence of the result, and an observation of the result is correlated with the presence of the toxin in the sample. A simplified assay where steps (a) and (b) are effected together also is provided, as is a cell bioassay for determining the sodium channel affect of a toxin in a fluid sample. A competitive assay for sodium channel-blocking toxins also is provided wherein the fluid sample and culture of cells are incubated with a medium comprising (i) an agent which causes persistent activation of the voltage-gated sodium channel and (ii) a sodium channel-activating toxin. Kits for performing the assays also are provided.