Isotonic suspensions of human erythrocytes were exposed to single electric pulses of intensity at a few kV/cm and duration in microseconds. Upon pulsation, the cell membranes became permeable to Na+ and K+, and the erythrocytes eventually hemolysed through the colloid osmotic effect of hemoglobin. The enhanced permeability is attributed to the formation of pores in the cell membranes. These pores are formed within a fraction of a microsecond, once the transmembrane potential induced by the applied electric field reaches a critical value of 1.0 V. Increased field intensity and pulse duration, or pulsation at low ionic strengths all expand the pore size, leading to an accelerated hemolysis reaction. In contrast to this expansion process, the initial step of pore formation is governed solely by the magnitude of the transmembrane potential: the critical value of the potential stays essentially constant in media of different ionc strengths, nor does it change appreciably with varying pulse duration. An abrupt increase in membrane permeability at a transmembrane potential around 1 V has been observed in many cellular systems. It is suggested that a similar mechanism of pore formation may apply to these systems as well.
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