Stable cavitation induces increased cytoplasmic calcium in L929 fibroblasts exposed to 1-MHz pulsed ultrasound

An increase in cytoplasmic calcium (Ca2+ increase) is a second messenger that is often observed under ultrasound irradiation. We hypothesize that cavitation is a physical mechanism that underlies the increase in Ca2+ in these experiments. To control the presence of cavitation, the wave type was controlled in a sonication chamber. One wave type largely contained a traveling wave (wave type A) while the other wave type largely contained a standing wave (wave type B). Fast Fourier transform (FFT) analysis of a sound field produced by the wave types ascertained that stable cavitation was present only under wave type A ultrasound irradiation. Under the two controlled wave types, the increase in Ca2+ in L929 fibroblasts was observed with fluorescence imaging. Under wave type A ultrasound irradiation, an increase in Ca2+ was observed; however, no increase in Ca2+ was observed under wave type B ultrasound irradiation. We conclude that stable cavitation is involved in the increase of Ca2+ in cells subjected to pulsed ultrasound.

► L929 fibroblasts were irradiated with pulsed ultrasound. ► Presence of cavitation was controlled with wave type in a sonication chamber. ► Stable cavitation was detected in one wave type with FFT analysis. ► Presence of stable cavitation coincided with calcium increase in L929.