Interaction of lipophilic ions with the plasma membrane of mammalian cells studies by electrorotation.

The electrical properties of biological and artificial membranes were studied in the presence of a number of negatively charged tungsten carbonyl complexes, such as [W(CO)5(CN)]- , [W(CO)5(NCS)]-, [W2(CO)10(CN)]-, and [W(CO)5(SCH2C6H5)]-, using the single-cell electrorotation and the charge-pulse relaxation techniques. Most of the negatively charged tungsten complexes were able to introduce mobile charges into the membranes, as judged from electrorotation spectra and relaxation experiments. This means that the tungsten derivatives act as lipophilic anions. They greatly contributed to the polarizability of the membranes and led to a marked dielectric dispersion (frequency dependence of the membrane capacitance and conductance). The increment and characteristic frequency of the dispersion reflect the structure, environment, and mobility of the charged probe molecule in electrorotation experiments with biological membranes. The partition coefficients and the translocation rate constants derived from the electrorotation spectra of cells agreed well with the corresponding data obtained from charge-pulse experiments on artificial lipid bilayers.