Electroporation is the phenomenon in which cell membrane permeability is increased by exposing the cell to short high electric field pulses. Experimental data show that the amount of permeabilization depends on the conductivity of the extracellular medium. If medium conductivity decreases then it is necessary to deliver a pulse of larger field amplitude in order to achieve the same effect. Models that do not take into account the permeabilization effect on the membrane conductivity cannot reproduce qualitatively the experimental observations. Here we employ an exponential function for describing the strong dependence of membrane conductivity on transmembrane potential. Combining that model with numerical methods we demonstrate that the dependence on medium conductivity can be explained as being the result of increased membrane conductance due to electroporation. As experimentally observed, extracellular conductivities of about 1 and 0.1 S m(-1) yield very similar results, however, for lower conductivities (<0.01 S m(-1)) the model predicts that significantly higher field magnitudes will be required to achieve the same amount of permeabilization.