Intravital microscopy at the single vessel level brings new insights of vascular modification mechanisms induced by electropermeabilization.

Electroporation/electropermeabilization, i.e. the result of the application of electric pulses to tissues, is a physical method for delivery of exogenous molecules into cells. It is effective particularly for compounds with limited transmembrane transport. In vivo, electropermeabilization facilitates the delivery of chemotherapeutic drugs into tumor cells that is the basic mechanism of the antitumor effectiveness of electrochemotherapy. This therapy has also blood flow modifying effects in tissues. The aim of our present study was to understand and explain the effects of electropermeabilization on the dynamics (vasomotricity, permeability and recovery) of subcutaneous blood vessels towards different size of molecules. These features were measured in C57Bl/6 mice via a dorsal skin fold window chamber, using fluorescently labeled dextrans of different sizes, intravital fluorescence microscopy imaging and specific image analysis. Application of electric pulses on the skin in vivo resulted in a rapid increase in vascular permeability that gradually recovered to basal levels at different times post-treatment, depending on dextran size. Simultaneously, the immediate constriction of the blood vessels occurred that was more pronounced for arterioles compared to venules. This vasoconstriction of arterioles results in a transient "vascular lock". The increased permeability of small vessels walls whatever the dextran size associated with delayed perfusion explains the improved delivery of the intravenous injected molecules (i.e. drugs, gene delivery) into the tissues induced by electropermeabilization in vivo.