9 カナダ東部麻痺性貝毒蔓延地域に生息するオオノガイが獲得した耐性機構(口頭発表の部)

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Paralytic shellfish poisoning (PSP) toxins such as Saxitoxin (STX) cause human fatalities by blocking Na^+ conductance in nerve fibers. Bivalve molluscs, the primary vectors of PSP in humans, show marked inter-species variation in their capacity to accumulate PSP toxins. Here we demonstrate that there is also inter-population variation in PSP resistance within a species. Softshell clam Mya arenaria were collected from two areas. One of them is subject to recurrent annual toxic blooms of Alexandrium spp. (PSP area), and the other has never suffered PSP up to date (PSP-free area). The clams from PSP area were far more tolerant to PSP toxins than those from PSP-free area, accumulated higher amount of toxicity, and survived. The amino acid sequences of voltage-dependent Na^+ channels in the pore regions, the binding site of STX, turned out to be different by only one amino acid between PSP toxin-sensitive and resistant clams. Patch clamp recording proved the substitution made the channel about 1,500-fold less sensitive to STX. This study establishes a molecular basis for intraspecific variation in toxin resistance to PSP.
2006-09-15