Fraction of transfected CHO cells. Fraction of transfected CHO cells after gene electrotransfer experiment in different electric field protocol. Cells were exposed to a train of eight pulses with amplitude of 200 V, duration 1 ms and repetition frequency 1 Hz. Results were obtained by means of fluorescence microscopy. Each value in the graph represent mean of four independent experiments, ± standard deviation. Electric field protocols result in different fraction of transfected cells (ANOVA: P = 0.002).