Ultrasound-induced Calcium Oscillations and Waves in Chinese Hamster Ovary Cells in the Presence of Microbubbles
Ronald E Kumon 1, Matthew Aehle 2, David Sabens 2, Paras Parikh 2, Dmitri Kourennyi 2 and Cheri X Deng 1*
1 University of Michigan
2 Case Western Reserve University
* To whom correspondence should be addressed. E-mail: cxdeng{at}umich.edu.
Submitted on May 22, 2007
Revised on June 4, 2007
Accepted on 27 June 2007
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Abstract |
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This study investigated the effects of ultrasound on the intracellular [Ca2+] of Chinese Hamster Ovary cells in the presence of albumin-encapsulated Optison microbubbles. Cells were exposed to 1 MHz ultrasound (tone burst of 0.2 s duration, 0.45 MPa peak pressure) while immersed in solution of 0.9 mM Ca2+. Calcium imaging of the cells was performed using digital video fluorescence microscopy and Ca2+-indicator dye fura-2AM. Experimental evidence indicated that ultrasound caused a direct microbubble-cell interaction resulting in the breaking and eventual dissolution of the microbubble and concomitant permeabilization of the cells to Ca2+. These cells exhibited a large influx of Ca2+ over 3-4 s and did not return to their equilibrium levels. Subsequently, some cells exhibited one or more Ca2+ oscillations with the onset of oscillations de-layed by 10-80 s after the ultrasound pulse. A variety of oscillations were observed including decaying oscillations returning to the baseline value over 35-100 s, oscillations superimposed on a more gradual recovery over 150-200 s, and oscillations continued with increased amplitude caused by a second ultrasound tone burst. The delays in onset appeared to result from calcium waves that propagated across the cells after the application of the ultrasound pulse.
Key Words:
calcium imaging, calcium oscillation, calcium wave, microbubble, sonoporation, ultrasound
