Relationship Between Dynamics of Bubbles Phagocytosed by Dendritic Cells and Intracellular Ca2+ Concentration Change Under Exposure to Pulsed Ultrasound

The possibility of intracellular Ca
²⁺
elevation being induced by short-pulsed ultrasound was investigated using cultured cells of the murine dendritic cell line DC2.4. Dendric cells (DCs) with phagocytosed microbubbles were irradiated by 3-cycle ultrasound of 0.2-0.6 MPa in peak-negative pressure to achieve safe and efficient mechanical stimulation. Two types of microbubbles, lipid-shell bubbles of about 1 µmn diameter and plastic-shell bubbles of 3–5 µm in diameter, were used to examine the effect of bubble dynamics on triggering Ca
²⁺
elevation and cell damage generation. Experimental results showed that, in the presence of microbubbles, even pulsed ultrasound at diagnostic levels could induce Ca
²⁺
elevation. It was also shown that the plastic-shell bubbles, which show contraction-only oscillation, can induce repetitive Ca
²⁺
elevations under multiple exposures of pulsed ultrasound. The results indicate that ultrasonic irradiation can induce sustained mechanical sensation of DCs, enhancing their antigen-presenting ability through cell maturation.