HepG2肝細胞的電泳實驗與模擬

Abstract

細胞電泳(electrophoresis of cells)是指生物細胞於外加電場的作用下，在電解質溶液中產生相對於靜止流體移動的現象，通常用於鑑定生物細胞的表面特性，包括細胞表面電荷、電位的電性與大小。本文以HepG2肝細胞為研究對象，從事電泳實驗與模擬。實驗部份，我們使用的儀器為ZetaSizer3000；探討的變因包括溶液的pH值、離子強度以及溶液中不同二價陽離子種類對細胞電泳遷移率的影響；而透過電泳實驗我們可以間接探討細胞表面的性質及官能基的種類。實驗結果顯示，電泳遷移率的絕對值隨pH值增加而遞增，隨離子強度增加而遞減。不同二價陽離子因為其與細胞表面官能基鍵結常數不同，而造成不同的電泳遷移率的變化。由電泳遷移率在pH 4.3左右以下變為正值，可以推論出HepG2肝細胞表面至少各含有一酸性及鹼性官能基。理論模擬分為兩部分：第一部分忽略電解質溶液中離子的大小；第二部份則考慮。系統為一表面覆蓋離子可穿透薄膜之粒子且薄膜內為電荷可調整的模型；重要的參數包括薄膜厚度、薄膜內酸鹼官能基的密度、酸鹼官能基解離常數及二價陽離子的鍵結常數。過程中使用FlexPDE軟體來求解主控方程式，有系統地找出適合的參數；並將兩部分模擬的結果和實驗數據相比較，以期解釋HepG2肝細胞的電泳行為。

Electrophoresis, the movement of a charged entity as a response to an applied electric field, is a useful tool to gather information about the charged conditions on cell surface. The electrophoretic behavior of HepG2 cells is investigated in this study both experimentally and theoretically. Experimentally, Zetasizer3000 is used to determine the mobility of HepG2 cells. Effects of pH, ionic strength, and different kinds of divalent cations are examined. We can discuss the properties and the kinds of functional groups on the surface of HepG2 cells by electrophoresis. The result shows that absolute mobility increases with increasing pH, and decreases with increasing ionic strength. Because of different binding constants with surface functional group, there is different mobility with different kinds of divalent cation. Under pH 4.3, the mobility of HepG2 cells reverses to positive sign, and we can therefore infer that there are at least one kind of acid functional group and one kind of base functional group on the surface of HepG2 cells. There are two parts in the theoretical modeling. The first one the ion size in the electrolyte is ignored, and in the second it is considered. A charge-regulated model is proposed to simulate the charged conditions on cell surface, and to estimate the key parameters such as the thickness of the membrane layer, the density, the dissociation constant of dissociable functional groups in the membrane layer, and the binding constant of divalent cation. FlexPDE software is used to solve the governing equations. These data are compared to the experimental data in order to estimate the suitable parameters. The results can be used to explain the electrophoresis behavior of HepG2 cells.