Passive electric properties of biological tissues such as permittivity and conductivity are important in applied problems of electrical stimulation in studying of human electromagnetic fields interactions and development of diagnostic and therapeutic procedures. The current densities and pathways resulting from an applied electrical stimulus are dictated to a large extent by the relative permittivity and specific conductivity of biological tissues; energy absorption also depends on tissue properties. We briefly present some theoretical basis for the current conduction in biologic materials and factors affecting the measurement of tissue dielectric properties that need to be taken into account when designing the measurement procedure. Large discrepancies between the data reported by different researchers are found in the literature, which are caused by factors such as different measuring techniques used, the fact that tissue samples were taken from different species, circumstances under which the measurements were performed, and many others. Electric properties of some biological tissues are summarized and data ranges of values found for relative permittivity and specific conductivity in the literature are given. Finally, we present some applications of bioimpedance measurements.

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Gene electrotransfer is gaining momentum as an efficient methodology for nonviral gene transfer. In skeletal muscle, data suggest that electric pulses play two roles: structurally permeabilizing the muscle fibers and electrophoretically supporting the migration of DNA toward or across the permeabilized membrane. To investigate this further, combinations of permeabilizing short high-voltage pulses (HV; hundreds of V/cm) and mainly electrophoretic long low-voltage pulses (LV; tens of V/cm) were investigated in muscle, liver, tumor, and skin in rodent models. The following observations were made: (1) Striking differences between the various tissues were found, likely related to cell size and tissue organization; (2) gene expression is increased, if there was a time interval between the HV pulse and the LV pulse; (3) the HV pulse was required for high electrotransfer to muscle, tumor, and skin, but not to liver; and (4) efficient gene electrotransfer was achieved with HV field strengths below the detectability thresholds for permeabilization; and (5) the lag time interval between the HV and LV pulses decreased sensitivity to the HV pulses, enabling a wider HV amplitude range. In conclusion, HV plus LV pulses represent an efficient and safe option for future clinical trials and we suggest recommendations for gene transfer to various types of tissues. 1261