Use of Perna viridis as a Bioindicator of Paralytic Shellfish Toxins at Low Pyrodinium bahamense var compressum Density using a Radioreceptor Assay
E.Z. SOMBRITO, M.C.V. HONRADO, A. DE VERA, R.S. TABBADA, MA.L. RAÑADA, J. RELOX JR., AND M.DC. TANGONAN
Philippine Nuclear Research Institute, Diliman, QC, Philippines
Bureau of Fisheries and Aquatic Resources, Diliman, QC, Philippines
A radioassay method, i.e. the Receptor Binding Assay, was used for studying the uptake of Paralytic Shellfish Poisoning (PSP) toxins in the green bay mussel Perna viridis highly consumed in the Philippines. This method allowed working at low cell density of Pyrodinium bahamense var compressum (~102-103 cells/L) representative of early stages of toxic algal blooms. The results indicated that within 16 hours toxic levels of PSP are reached in the tissues of P. viridis, confirming the suitability of the green mussel as an indicator organism for paralytic shellfish toxicity in bivalves during the early stages of the bloom. Results also demonstrated that the weight-specific toxicity significantly increased with mussel size reduction. This method, based on the competition between the labeled and unlabeled toxin for the sodium channel receptor, offers better sensitivity than the mouse bioassay method. With an increasing amount of toxins in the sample, the amount of radiolabeled toxin binding with the receptor decreases. The amount of radiolabeled toxin (tritiated saxitoxin) is then measured using liquid scintillation counting. Quantification is based on a competition curve established by measuring competitive binding on a rat brain membrane with known concentrations of saxitoxin.
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