Duration of ultrasound bubbles enhanced cell membrane permeability

Purpose: Ultrasound (US) has shown the ability to modulate the cell membrane permeability in a process known as sonoporation. In addition, the sonoporation process has been proven to be amplified when US is associated with contrast microbubbles. The purpose of this study is to quantify the duration of the sonoporation process for external molecules with different sizes. Method: monolayers of Chinese Hamster Ovary (CHO) cells, fixed on a membrane, were used and 3 fluorescent-labeled dextran molecules (10, 40 and 70 KDa) were used as markers. The US settings consisted of a burst of 10 cycles and 1 MHz at acoustic pressures between 0.2-1.0 MPa with a pulse repetition rate of 20 Hz. CHO cells were irradiated at 37°C for 2 minutes after addition of microbubbles in a ratio of 1:1 cell. The cells were incubated with the 3 markers at t=0 sec, 10 sec, 30 sec, and 60 sec after US was applied and the respective uptake levels were measured. Conclusion: a negative correlation between maximum uptake and time after turning off US is demonstrated. Moreover, a higher maximum uptake level at the moment of ultrasound turn off results in a faster decay in uptake. In conclusion the duration of enhanced membrane permeability is limited with a maximal duration less than 60 sec. This depends on the size of the molecules but not on MI.