How transient alterations of organelles in mammalian cells submitted to electric field may explain some aspects of gene electrotransfer process

• Electric pulses can induce ultrastructural alterations in cells.
• Transient alterations are observed at the mitochondria and nucleus levels.
• These alterations may have direct consequences on DNA electrotransfer.

Electric pulses can be used to transiently permeabilize the cell plasma membrane. This method is nowadays employed as a safe and efficient means to deliver therapeutic molecules into target cells and tissues. Despite the large bulk of literature on this topic, there is a lack of knowledge about the mechanism(s) of molecule delivery. The behavior of the cells both while the field is on and after its application is indeed not well described. Questions about cell organelle alterations remain unanswered. We report here evidence for a number of ultrastructural alterations in mammalian cells exposed to electric pulses. Specifically, CHO cells were subjected to trains of 10 pulses lasting 5 ms using an electric field of 800 V/cm, i.e. under conditions leading both to membrane permeabilization, gene transfer and expression. Cells were observed to undergo morphological alterations of the mitochondria and nucleus. These modifications, detected in the minutes following pulse delivery, were transient. They may have direct consequences on molecule delivery and therefore may explain various aspects of the mechanisms of DNA electrotransfer.