Localization of pufferfish saxitoxin and tetrodotoxin binding protein (PSTBP) in the tissues of the pufferfish, Takifugu pardalis, analyzed by immunohistochemical staining.

Pufferfish saxitoxin and tetrodotoxin binding protein (PSTBP) was previously isolated from the plasma of the marine pufferfish, Takifugu pardalis. In this study, we investigated distribution pattern of PSTBP in intestine, liver, ovary, skin, and skeletal muscle of T. pardalis by immunohistochemical staining for the study of functions of this protein. In the skin, dermis around the tetrodotoxin secreting gland was positive, while this secreting gland itself was negative. In the ovary containing vitellogenic oocytes, ovarian wall and vitelline envelope were positive, while yolk and nucleus were negative. In the liver, hepatocytes with large fat droplets and capillaries were positive. In the intestine, the lamina propria mucosae were positive, while the mucosal epithelium was negative. In the skeletal muscle, only capillaries were positive. Furthermore, liver specific expression of PSTBP was confirmed by Northern blot analysis. Based on these results together with reported tetrodotoxin localization pattern in pufferfish, PSTBP was assumed to be a carrier protein to transfer tetrodotoxin among the tissues, especially liver, ovary, and skin.