| Co-Investigator(Kenkyū-buntansha) |
SASAKI Makoto School of Science, The University of Tokyo, Lecturer, 大学院・理学系研究科, 講師 (80235267)
TACHIBANA Kazuo School of Science, The University of Tokyo, Professor, 大学院・理学系研究科, 教授 (70142081)
KONOKI Keiichi School of Science, The University of Tokyo, Research Associate, 大学院・理学系研究科, 助手 (40292825)
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| Research Abstract |
Maitotoxin (MTX) was first discovered as one of the toxins responsible for ciguatera, a seafood poisoning caused by ingestion of coral reef fish. MTX has extremely potent bioactivities ; its toxicity is particularly worth noting, since its LD_<50>(50 ng/kg, mouse ip.) is exceeded only by a few proteinaceous toxins. MTX elicits Ca^<2+> influx in virtually all cells and tissues and this elevation in intracellular calcium concentration leads to secondary events ; e.g., phosphoinositide breakdown, arachidonic acid release, muscle contraction, and secretion of dopamine, norepinephrine, and insulin. Gangliosides GM1 and GM3 strongly inhibited MTX-induced Ca^<2+> influx in C6 cells. Their inhibitory potency was in the order GM1 (IC_<50>, ca. 2 μM)>GM3 (ca. 5 μM)>asialo-GM1 (ca. 20 μM). GM1 (3 μM) completely blocked MTX(30 nM)-induced Ca^<2+> influx in human erythrocyte ghosts. When C6 cells were pretreated with tunicamycin, an antibiotic which inhibits N-linked glycosylation, or concanavalin A, a lectin which exhibits high affinity for cell-surface oligosaccharides, MTX-induced Ca^<2+> influx was significantly potentiated. This suggests that removal of oligosaccharides from the cell surface by tunicamycin or capping of sugar chains on plasma membranes by concanavalin A can potentiate the action of MTX.Photoaffinity labeling experiment to identify MTX-binding protein was carried out with use of a daizirine-biotin conjugated reagent developed by Hatanaka. Some spots on 2D electrophoresis, corresponding to 2 KDa were eliminated by addition of an MTX inhibitor, brevetoxin-B.
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