HIGH -RESOLUTION IMAGING OF INTRACELLULAR CALCIUM FLUCTUATIONS CAUSED BY OSCILLATING MICROBUBBLES

Ultrasound insonification of microbubbles can locally enhance drug delivery, but the microbubble- cell interaction remains poorly understood. Because intracellular calcium (Ca-i(2+)) is a key cellular regulator, unraveling the Ca-i(2+) fluctuations caused by an oscillating microbubble provides crucial insight into the underlying bio-effects. Therefore, we developed an optical imaging system at nanometer and nanosecond resolution that can resolve Ca-i(2+) fluctuations and microbubble oscillations. Using this system, we clearly distinguished three Ca-i(2+) i uptake profiles upon sonoporation of endothelial cells, which strongly correlated with the microbubble oscillation amplitude, severity of sonoporation and opening of cell - cell contacts. We found a narrow operating range for viable drug delivery without lethal cell damage. Moreover, adjacent cells were affected by a calcium wave propagating at 15 mm/s. With the unique optical system, we unraveled the microbubble oscillation behavior required for drug delivery and Ca-i(2+) fluctuations, providing new insight into the microbubble-cell interaction to aid clinical translation. (E-mail addresses: d.beekers@erasmusmc.nl, k.kooiman@erasmusmc.nl) (c) 2020 The Author(s). Published by Elsevier Inc. on behalf of World Federation for Ultrasound in Medicine & Biology. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/).