Comparison between the in vivo and in vitro measurements of luciferase activity of tibial cranial muscle after electrotransfer with a luciferase-encoding plasmid. Values are mean +/- SEM (n = 10) of the integrated values of luminescence in ROI of the tibial cranial muscle 8 days after electrotransfer of 0.3, 3 or 30 μg of pC1 luc plasmid as measured in vivo (white columns) and in vitro 3 hours later or more (grey columns) on the same muscles. Individual values are represented by black triangles and the lines link values measured in vivo and in vitro for the same muscles. In vivo background luminescence was subtracted from the luminescence measured. In vitro, background luminescence was negligible. Dose effect: – in vitro **** p < 0.0001 between electrotransfer with 0.3 and 3 μg of plasmid ** p < 0.01 between 3 and 30 μg of plasmid – in vivo $$ p < 0.01 between electrotransfer with 0.3 and 3 μg of plasmid.