| Summary: | 碩士 === 國立臺灣大學 === 生理學研究所 === 94 === Beauvericin (BEA) was first identified in an insect-pathogenic fungus, Beauveria bassiana. In vitro studies demonstrated that BEA induced significant cell deaths in insect, murine, and human tumor cell lines. In mammalian cell lines, BEA is known to induces a significant increase in intracellular Ca2+ concentration ([Ca2+]i) that leads to a combination of cellular apoptotic and necrotic responses. However, the source of [Ca2+]i increase remains inconclusive. Since the the mechanism of BEA-induced [Ca2+]i increase is not clear, we investigate the mechanism of BEA-induced [Ca2+]i increase and the sources of [Ca2+]i increase. We also investigate the correlation between Ca2+ influx and BEA cytotoxic effects. The goal of this thesis is to demonstrate whether BEA is able to increase [Ca2+]i , where [Ca2+]i increase comes from, and whether this [Ca2+]i increase is correlated with BEA-induced cytotoxic effects.
Two-electrode voltage clamp method was used to record BEA-induced currents in Xenopus laevis oocytes. BEA was found to activate endogenous Ca2+_activated Cl- currents in Xenopus oocytes, suggesting a significant [Ca2+]i increase by the mycotoxin. BEA-induced currents in oocytes were blocked by the removal of extracellular Ca2+, indicating extracellular Ca2+ influx as the source of BEA [Ca2+]i effect. In addition, BEA was capable of induce potent cytotoxic effects in oocytes, the effect of which was significantly diminished in the absence of extracellular Ca2+.
Based on our results, we conclude that the mechanism of BEA-induced [Ca2+]i can be attributed to a mobilization of Ca2+ influx from external bath solution, which in turn activates Ca2+_activated Cl- channels in Xenopus oocytes. In addition, BEA-induced Ca2+ influx contributes to, but is not prerequisite to, the cytotoxic effects of BEA that eventually lead to cell deaths. According to our result, we speculate that the mechanism of BEA-induced cell deaths in Xenopus oocytes involves an increase [Ca2+]i through extracellular Ca2+ influx, which eventually activates Ca2+-sensitive cell death pathway.
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