Frequency-dependent Calcium Dynamics in Ultrasound Mechanotransduction

Calcium signaling is a second messenger that triggers physiological changes at the cellular level, such as proliferation, differentiation, or apoptosis. It was recently found that calcium dynamics play a vital role in many studies, including cancer, Alzheimer's disease, and Parkinson's disease, and we studied how intracellular signaling pathways work by ultrasound mechanotransduction. However, since ultrasound mechanotransduction does not yet have many experimental results by the quantified ultrasound parameters, little is known about the mechanism between ultrasound parameters and calcium dynamics We investigate calcium level changes using different frequencies of ultrasound to study intracellular signal pathways of fibroblasts, which may function as one of the contributing factors of tissue repair. We quantified a few major ultrasound stimulation parameters, i.e., operating frequency, beam width, and acoustic pressure. Three 40 MHz ultrasound transducers with different f-numbers (0.8, 1.0, and 1.5) were designed and fabricated. During the cell stimulation, ultrasound waves with different frequencies (36, 45, and 69 MHz) but the same beam width and same acoustic pressure were exerted on the cells. The cell lines used were NIH/3T3 fibroblasts. At the fixed acoustic pressure and beam width, intracellular calcium level increased more rapidly at higher frequencies, which shows that the intracellular signal pathways of fibroblasts may be mainly dependent upon the frequency used for stimulation.