Analysis of paralytic shellfish poisoning toxin congeners by a sodium channel receptor binding assay

This study was carried out to characterize the detection and quantitation of several paralytic shellfish poisoning (PSP) toxin congeners using a receptor binding assay (RBA). This involved competitive binding of the toxin congeners against tritium-labeled STX for receptor sites on rat brain sodium channels. Competitive binding curves were described by a four-parameter logistic equation. Half-saturation values (EC50) ranged from 4.38 nM for STX to 142 nM for GTX5. Receptor binding affinity was in the order STX > GTX1/4 > neoSTX > GTX2/3 > dcSTX > GTX5, and this was similar to the order of mouse toxicity of these congeners. Predicted toxin concentrations from observed STXeq values and EC50 ratios relative to STX were within 20% or better-of the actual concentrations used in the assay. In contrast predicted toxin concentrations using mouse toxicity ratios relative to STX did not provide a good match to actual concentrations, except for GTX I A. This study has shown that the rat brain sodium channel RBA will provide a reliable integration of total toxicity of various PSP toxin congeners present in a sample. (C) 2004 Elsevier Ltd. All rights reserved.