The size of sonoporation pores on the cell membrane

Sonoporation generates transient pores on the cell membrane and has been exploited as a promising intracellular drug and gene delivery strategy. The size of the pores in the membrane resulting from sonoporation determines the size of molecules or agents that can be delivered using the technique. However, size information has not been readily available due to the challenges in measuring dynamic, submicron-sized pores. Post ultrasound assays such as AFM or SEM, often time consuming and labor intensive, have been used to gauge pore size but are intrinsically limited to static measurements that may not accurately represent the relevant size. We have previously demonstrated the utility of voltage clamp techniques for monitoring sonoporation in real time via the trans-membrane current (TMC) change of a single cell under voltage clamp. Using Xenopus oocytes as the model system in this study, the TMC change during sonoporation (0.2 s, 0.3 MPa, 1 MHz) of single cells in solution with Definity microbubbles was recorded in a whole cell voltage clamp configuration. As the changes of the TMC are related to the diffusion of ions through the pores on the membrane, they can potentially provide relevant information of the pore size generated in sonoporation. By controlling the microbubble concentration, experiments were designed to allow measurement of the TMC corresponding to a single pore on the membrane. An electro-diffusion model was developed to relate the TMC with pore size from the ion flow through the pores on the membrane.