DEFORMABILITY AND STABILITY OF ERYTHROCYTES IN HIGH-FREQUENCY ELECTRIC-FIELDS DOWN TO SUBZERO TEMPERATURES

High-frequency electric fields can be used to induce deformation of re d blood cells. In the temperature domain T = 0 degrees to -15 degrees C (supercooled suspension) and for 25 degrees C this paper examines fo r human erythrocytes (discocytes, young cell population suspended in a low ionic strength solution with conductivity sigma(25 degrees) = 154 mu S/cm) in a sinusoidal electric field (v = 1 MHz, E-0 = 0-18 kV/cm) the following properties and effects as a function of field strength and temperature: 1) viscoelastic response, 2) (shear) deformation (ste ady-state value obtained from the viscoelastic response time), 3) stab ility (by experimentally observed breakdown of cell polarization and h emolysis), 4) electrical membrane breakdown and field-induced hemolysi s (theoretical calculations for ellipsoidal particles), and 5) mechani cal hemolysis. The items 2-4 were also examined for the frequency v = 100 kHz and for a nonionic solution of very low conductivity (sigma(25 degrees) = 10 mu S/cm) to support our interpretations of the results for 1 MHz. Below 0 degrees C with decreasing temperature the viscoelas tic response time tau(res)(T) for the cells to reach steady-state defo rmation values d(infinity,E) increases and the deformation d(infinity, E)(T) decreases strongly. Both effects are especially high for low fie ld strengths. The longest response time of similar to 30 s was obtaine d for -15 degrees C and small deformations. For 1 MHz the cells can be highly elongated up to 2.3 times their initial diameter a, for 25 deg rees and 0 degrees C, 2.1a(0) for -10 degrees C and still 1.95a(0) for -15 degrees C. For T greater than or equal to 0 degrees C the deforma tion is limited by hemolysis of the cells, which sets in for E-lysis(0 )(25 degrees) approximate to 8 kV/cm and E-lysis(0)(0 degrees) approxi mate to 14 kV/cm. These values are approximately three times higher th an the corresponding calculated critical field strengths for electrica lly induced pore formation. Nevertheless, the observed depolarization and hemolysis of the cells is provoked by electrical membrane breakdow n rather than by mechanical forces due to the high deformation. For th e nonionic solution, where no electrical breakdown is expected in the whole range for E-0, the cells can indeed be deformed to even higher v alues with a low hemolytic rate. Below 0 degrees C we observe no hemol ysis at all, not even for the frequency 100 kHz, where the cells hemol yze at 25 degrees C for the much lower field strength E-lysis(0) appro ximate to 2.5 kV/cm. Obviously, pore formation and growth are weak for subzero temperatures.