Gascoyne P, Pethig R, Satayavivad J, Becker F F, Ruchirawat M
Section of Experimental Pathology, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Biochim Biophys Acta. 1997 Jan 31;1323(2):240-52. doi: 10.1016/s0005-2736(96)00191-5.
The dielectric properties of normal erythrocytes were compared to those of cells infected with the malarial parasite Plasmodium falciparum. Normal cells provided stable electrorotation spectra which, when analyzed by a single-shelled oblate spheroid dielectric model, gave a specific capacitance value of 12 +/- 1.2 mF/m2 for the plasma membrane, a cytoplasmic permittivity of 57 +/- 5.4 and a cytoplasmic conductivity of 0.52 +/- 0.05 S/m. By contrast, parasitized cells exhibited electrorotation spectra with a time-dependency that suggested significant net ion outflux via the plasma membrane and it was not possible to derive reliable cell parameter values in this case. To overcome this problem, cell membrane dielectric properties were instead determined from dielectrophoretic crossover frequency measurements made as a function of the cell suspending medium conductivity. The crossover frequency for normal cells depended linearly on the suspension conductivity above 20 mS/m and analysis according to the single-shelled oblate spheroid dielectric model yielded values of 11.8 mF/m2 and 271 S/m2, respectively, for the specific capacitance and conductance of the plasma membrane. Unexpectedly, the crossover frequency characteristics of parasitized cells at high suspending medium conductivities were non-linear. This effect was analyzed in terms of possible dependencies of the cell membrane capacitance, conductance or shape on the suspension medium conductivity, and we concluded that variations in the membrane conductance were most likely responsible for the observed non-linearity. According to this model, parasitized cells had a specific membrane capacitance of 9 +/- 2 mF/m2 and a specific membrane conductance of 1130 S/m2 that increased with increasing cell suspending medium conductivity. Such conductivity changes in parasitized cells are discussed in terms of previously observed parasite-associated membrane pores. Finally, we conclude that the large differences between the dielectrophoretic crossover characteristics of normal and parasitized cells should allow straightforward sorting of these cell types by dielectrophoretic methods.
将正常红细胞的介电特性与感染疟原虫恶性疟原虫的细胞的介电特性进行了比较。正常细胞提供了稳定的旋转电泳光谱，当通过单壳扁球体介电模型进行分析时，质膜的比电容值为12±1.2 mF/m²，细胞质介电常数为57±5.4，细胞质电导率为0.52±0.05 S/m。相比之下，被寄生的细胞表现出具有时间依赖性的旋转电泳光谱，这表明通过质膜有显著的净离子外流，在这种情况下无法得出可靠的细胞参数值。为了克服这个问题，细胞膜的介电特性改为根据作为细胞悬浮介质电导率函数的介电泳交叉频率测量来确定。正常细胞的交叉频率在高于20 mS/m时线性依赖于悬浮电导率，根据单壳扁球体介电模型分析得出质膜的比电容和电导率值分别为11.8 mF/m²和271 S/m²。出乎意料的是，在高悬浮介质电导率下被寄生细胞的交叉频率特性是非线性的。根据细胞膜电容、电导或形状对悬浮介质电导率的可能依赖性对这种效应进行了分析，我们得出结论，膜电导的变化最有可能是观察到的非线性的原因。根据这个模型，被寄生的细胞具有9±2 mF/m²的比膜电容和1130 S/m²的比膜电导，其随着细胞悬浮介质电导率的增加而增加。根据先前观察到的与寄生虫相关的膜孔来讨论被寄生细胞中的这种电导率变化。最后，我们得出结论，正常细胞和被寄生细胞的介电泳交叉特性之间的巨大差异应该允许通过介电泳方法直接分选这些细胞类型。
