Reversible Ca(2+) signaling and enhanced paracellular transport in endothelial monolayer induced by acoustic bubbles and targeted microbeads.

Ultrasound and microbubble mediated blood brain barrier opening is a non-invasive and effective technique for drug delivery to targeted brain region. However, the exact mechanisms are not fully resolved. The influences of Ca(2+) signaling on sonoporation and endothelial tight junctional regulation affect the efficiency and biosafety of the technique. Therefore, an improved understanding of how ultrasound evokes Ca(2+) signaling in the brain endothelial monolayer, and its correlation to endothelial permeability change is necessary. Here, we examined the effects of SonoVue microbubbles or integrin-targeted microbeads on ultrasound induced bioeffects in brain microvascular endothelial monolayer using an acoustically-coupled microscopy system, where focused ultrasound exposure and real-time recording of Ca(2+) signaling and membrane perforation were performed. Microbubbles induced robust Ca(2+) responses, often accompanied by cell poration, while ultrasound with microbeads elicited reversible Ca(2+) response without membrane poration. At the conditions evoking reversible Ca(2+) signaling, intracellular Ca(2+) release and reactive oxygen species played key roles for microbubbles induced Ca(2+) signaling while activation of mechanosensitive ion channels was essential for the case of microbeads. Trans-well diffusion analysis revealed significantly higher trans-endothelial transport of 70 kDa FITC-dextran for both integrin-targeted microbeads and microbubbles compared to the control group. Further immunofluorescence staining showed disruption of cell junctions with microbubble stimulation and reversible remodeling of many cell junctions by ultrasound with integrin-targeted microbeads. This investigation provides new insights for ultrasound induced Ca(2+) signaling and its influence on endothelial permeability, which may help develop new strategies for safe and efficient drug/gene delivery in the vascular system.