INTERACTION OF LIPOPHILIC IONS WITH THE PLASMA-MEMBRANE OF MAMMALIAN-CELLS STUDIED BY ELECTROROTATION

The electrical properties of biological and artificial membranes were studied in the presence of a number of negatively charged tungsten car bonyl complexes, such as [W(CO)(5)(CN)](-), [W(CO)(5)(NCS)](-), [W-2(C O)(10)(CN)](-), and [W(CO)(5)(SCH2C6H5)](-), using the single-cell ele ctrorotation and the charge-pulse relaxation techniques. Most of the n egatively charged tungsten complexes were able to introduce mobile cha rges into the membranes, as judged from electrorotation spectra and re laxation experiments. This means that the tungsten derivatives act as lipophilic anions. They greatly contributed to the polarizability of t he membranes and led to a marked dielectric dispersion (frequency depe ndence of the membrane capacitance and conductance). The increment and characteristic frequency of the dispersion reflect the structure, env ironment, and mobility of the charged probe molecule in electrorotatio n experiments with biological membranes. The partition coefficients an d the translocation rate constants derived from the electrorotation sp ectra of cells agreed well with the corresponding data obtained from c harge-pulse experiments on artificial lipid bilayers.