In vivo electroporation of skeletal muscle: threshold, efficacy and relation to electric field distribution

In vivo electroporation is increasingly being used to deliver small molecul es as well as DNA to tissues. The aim of this study was to quantitatively i nvestigate in vivo electroporation of skeletal muscle, and to determine the threshold for permeabilization, We designed a quantitative method to study in vive electroporation, by measuring uptake of Cr-51-EDTA. As electrode c onfiguration influences electric field (E-field) distribution, we developed a method to calculate this. Electroporation of mouse muscle tissue was inv estigated using either external plate electrodes or internal needle electro des placed 4 mm apart, and eight pulses of 99 mu s duration at a frequency of 1 Hz. The applied voltage to electrode distance ratio was varied from 0 to 2.0 kV/cm. We found that: (1) the threshold for permeabilization of skel etal muscle tissue using short duration pulses was at an applied voltage to electrode distance ratio of 0.53 kV/cm (+/-0.03 kV/cm), corresponding to a n E-field of 0.45 kV/cm; (2) there were two phases in the uptake of Cr-51-E DTA, the first indicating increasing permeabilization and the second indica ting beginning irreversible membrane damage; and (3) the calculated E-field distribution was more homogeneous for plate than for needle electrodes, wh ich was reflected in the experimental results. (C) 1999 Elsevier Science B. V. All rights reserved.