Interaction of fluorinated lipophilic ions with the plasma membrane of mammalian cells studied by electrorotation and dielectrophoresis

Two complementary AC electrokinetic techniques electrorotation (ROT) and dielectrophoresis (DEP) were employed for studying the interaction of the fluorinated tungsten anion [W(CO)5(SC6H4CF3)]− and a number of its derivatives with the plasma membrane of mouse myeloma cells. The use of microstructured electrodes allowed the measurements to be performed over wide ranges of field frequency and medium conductivity. At micromolar concentrations, most of the fluorinated anions gave rise to dramatic changes in the low-frequency part of both ROT and DEP spectra of cells, indicating that these compounds acted as lipophilic anions capable of introducing large amounts of mobile charges into the plasma membrane. Application of the theoretical models linking the ROT and DEP responses yielded not only the passive electrical properties of the plasma membrane and cytosol but also the ion transport parameters, such as the surface concentration and translocation rate of the lipophilic ions dissolved in the plasma membrane. This study demonstrated that combined ROT and DEP measurements can be employed as a powerful experimental tool for the analysis of the complex relationships between the molecular structure and membrane permeability of charged lipophilic compounds. Due to their strong lipophilicity and fairly low cytotoxicity, the fluorinated tungsten compounds presented here appear to provide a promising new class of field-sensitive molecular probes for membrane structure and transport studies.