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Determination of toxicity equivalent factors for paralytic shellfish toxins by electrophysiological measurements in cultured neurons.

The establishment of toxicity equivalent factors to develop alternative methods to animal bioassays for marine-toxin detection is an urgent need in the field of phycotoxin research. Paralytic shellfish poisoning (PSP) is one of the most severe forms of food poisoning. The toxins responsible for this type of poisoning are highly toxic natural compounds produced by dinoflagellates, which bind to voltage-gated Na(+) channels causing the blockade of action potential propagation. In spite of the fact that several standards of PSP toxins are currently commercially available, there is scarcity of data on the biological activity of these toxins, a fact that limits the calculation of their toxicity equivalent factors. We have evaluated the potency of the commercial PSP toxin standards for their ability to inhibit voltage-dependent sodium currents in cultured neuronal cells by electrophysiological measurements. The in vitro potencies of the PSP toxin standards as indicated by their IC(50) values were in the order Neosaxitoxin (NeoSTX) > decarbamoylsaxitoxin (dcSTX) > saxitoxin (STX) > gonyautoxin 1,4 (GTX1,4) > decarbamoylneosaxitoxin (dcNeoSTX) > gonyautoxin 2,3 (GTX2,3) > decarbamoylgonyautoxin 2,3 (dcGTX2,3) > gonyautoxin 5 (GTX5) > N-sulfocarbamoyl-gonyautoxin-2 and -3 (C1,2). The data obtained in this in vitro analysis correlated well with their previously reported toxicity values.