Intracellular calcium oscillation in MG-63 cells induced by steady and pulsed shear stresses

Abstract

An optically transparent micro-cell chip was fabricated with a polydimethylsiloxane (PDMS) channel structure and cover glass and was used to examine the intracellular calcium responses of a single cell to steady and pulsed shear stresses of various durations to investigate the optimal duration of mechanical stimulation in MG-63 cells (human osteoblast-like bone cell line). Intracellular calcium responses were measured using a laser-scanning microscope under varying extracellular mechanical environments. Shear stress in the micro-channel was applied as mechanical stimulation and generated using a computer-controlled pneumatic system. The intracellular calcium expression under various shear stresses was measured to investigate the effect of the magnitude of the shear stress to intracellular responses. The magnitude of the averaged calcium intensity under 5 dyne/cm 2 of shear stress was larger than that under 27 dyne/cm 2 of shear stress. The rising times of the calcium intensity to 5 and 27 dyne/cm 2 of shear stress were almost identical, but their falling times from 90% to 10% of the normalized intensity were different. The falling time of the intracellular responses under the higher shear stress was slightly shorter than that under the lower shear stress. The optimal duration of mechanical stimulation was determined based on the measured static and dynamic characteristics of the internal cellular signals. We concluded that biochemical signals were highly dependent on the period of applied shear stress. Additionally, the most effective period for shear stress is that matching the duration of internal signaling. A reasonable duration of dynamic mechanical stimulation is approximately 176 ± 32 s when 5 dynes/cm 2 of shear stress is applied to cells. This can provide a simple and effective methodology for determining the proper duration of mechanical stimulation for cells.