Isotonic suspensions of erythrocytes were exposed to intense electric fields for a duration in microseconds. Time-dependent increase in the conductivity of the suspension was observed under fields greater than a threshold of about 1.5 kV/cm. The threshold was independent of the ionic strength of the medium, and changed little with temperature or with the rise time of the applied field. Under fields greater than 3 kV/cm, the time course of the conductivity increase consisted of a rapid (approx. 1 μs) and a slow (approx. 100 μs) phases. The increase is attributed primarily to large membrane conductance induced by the applied field. The membrane conductance is in the order of 10 Ω-1/cm2 in the rapid phase and 102 Ω-1/cm2 in the slow phase. Comparison with previous results indicates that this induced membrane conductance corresponds to the formation of aqueous pores in the cell membrane. After the applied field was removed, the conductivity of the suspension returned nearly to its initial value, indicating that the induced membrane conductance is strongly dependent on the membrane potential. The conductivity then increased again in the time range of 10 s. This is attributed to the diffusional efflux of intracellular ions through the voltage-induced pores. From the rate of the efflux, number of the pores/cell is estimated to be in the order of 102. Final stage of the conductivity change was a slow decrease, corresponding to the colloid osmotic swelling of the perforated cells.
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