Effects of electrical pulses on the dielectric properties of biological cells

Despite a basic knowledge of cells' biochemical processes, their electrical properties, particularly the changes in membrane properties upon the application of pulsed electric fields (PEF's), have not yet been fully characterized. Microsecond pulses above a certain threshold cause electroporation of the cell membrane while nanosecond pulses of higher voltage additionally porate the inner organelles. We used Time Domain Dielectric Spectroscopy to measure the conductivity of HL-60 (human leukemia) cell suspensions as a function of time after 10 ns, 78.5 kV/cm pulses and 50 /spl mu/s, 1.1 kV/cm pulses, which have the same energy. The conductivity increased immediately after the 50 /spl mu/s pulse, indicating that ion channels in the HL-60 membranes initially opened. However, the conductivity decreased immediately after the ultrashort pulse, indicating that ion channels initially closed. The conductivity decreases significantly approximately 40 minutes after both pulses. This suggests that not only do the pores or channels opened close, but pores or channels open in the membrane prior to the pulse may close as well. These measurements were an intermediate step in determining the electrical properties of HL-60 cells using a two-shell model. Once determined, these electrical parameters will be used in electroporation models developed at Old Dominion University.