台灣眼鏡蛇毒蛋白裡其中一個主要的成分為心臟毒素，各個心臟毒蛋白(cardiotoxin)之間為一個結構相似的β-板狀(β-sheet polypeptides)且帶有正電荷的蛋白，使被咬傷者的心肌收縮而停止跳動，但是對於其進入細胞後的詳細作用並不是很清楚。在利用共軛焦顯微鏡觀察下，我們可以發現心臟毒素A2、A4會明顯的累積於溶酶體上。而實驗室之前的研究已經指出心臟毒素A2、A4進入細胞的方式是藉由巨胞飲作用(Macropinocytosis)以及胞膜窖引導的內吞作用(Caveolae-mediated endpcytosis)。且脂筏在過去的研究中被認為是調控細胞進行內吞作用的重要角色，因此需要進一步探討它對心臟毒素的內吞作用所造成的影響。
在實驗中我們發現膽固醇能夠調控心臟毒素A2、A4進入細胞，影響心臟毒素A2、A4進入細胞的量和進入細胞的位置。在增加細胞膜上的膽固醇含量後可以觀察到心臟毒素A2、A4聚集在溶酶體的程度相較於正常狀況下會有程度上的增加，且心臟毒素A2、A4能夠進一步的影響溶酶體的pH值。從觀察到的實驗結果可以推測溶酶體可能是心臟毒素A2、A4在細胞中的攻擊對象，進而導致心肌細胞的死亡。

Cardiotoxins (CTXs), a major component of snake venom from Taiwan cobra Naja atra, are structurally homologues beta-sheet basic polypeptides that are known to manifest cytotoxicity in cells, but the mechanism of their action remains obsecure. Using the confocal imaging technique, we show that cardiotoxins can get into H9C2 cells and accumulate markedly in lysosomes. And the previous study has shown that CTX A2 and CTXA4 internalize through dynamin-dependent macropinocytosis and it has proved that they can also internalize through clathrin mediated pathway. However, lipid rafts are implicated in endocytosis. So membrane lipid raft is needed to further investigate if it affects cargo internalization.
In this study, we found that cholesterol incorporation can enhance the internalization of CTX A2 and CTXA4. And we observe that CTXA2 and CTXA4 can target to lysosome at higher level compared to normal and cholesterol deplete condition. On the basis of the results obtained, we propose that lysosomes may be the primary target of CTX A2 and CTXA4. CTXs may not degraded in lysosomes, it has possibility to make lysosome damage to release lysosomal extracts. So we try to test the lysosomal integrity and check the relative effects of CTXs on lysosmes of living cultured cells. And these data indicate that CTXA2 and CTXA4 may inhibits the acidification of lysosome. This may provide us some possibility of how CTXs make H9C2 cells toxicity.

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