Visualization of the DNA/membrane interaction and the actin cytoskeleton in CHO cells after application of the electric field. CHO cells transiently expressing the EGFP-actin protein were pulsed in the presence of POPO-3 labeled plasmid DNA (pEGFP-C1) with the following parameters: 10 pulses of 5 ms at 0.4 kV/cm and 1 Hz. The observations were performed using wide field microscopy between 5 and 30 minutes after application of the electric field. (a,d,g,j) POPO-3 labeled DNA, (b,e,h,k) EGFP-actin protein expression, (c,f,i,l) merge of the two channels (18 cells clearly showed colocalization between DNA and actin). The black arrow on the right side indicates the direction of the electric field. Bar = 5 µm. CHO, Chinese hamster ovary; EGFP, enhanced green fluorescence protein.