Prolonged mechanical stretch (PMS) triggers the calcium oscillations in hMSCs without spontaneous activities.

<p>(A) A schematic drawing of PMS application. Cells were seeded on polyacrylamide (PA) gels with 20 kPa of elastic modulus and a glass capillary probe tip can be placed near a cell and inserted in the gel to pull the gel and cause the stretch of the target cell. The right images show typical displacement and strain maps during prolonged mechanical stretch. The cold and hot colors represent the small and large relative displacement (top, 0–15 µm) and strain index (bottom, 0–0.3). (B) Mechanical stretch was applied to the cytosolic FRET biosensor-transfected hMSC and intracellular calcium dynamics were visualized by the FRET ratio. High FRET ratio (Red color) denotes high concentration of calcium. White arrow points to the direction of mechanical stretch. ON: calcium increase, OFF: calcium decrease. Scale bar, 20 µm. (C) The time course shows that PMS triggers the calcium oscillations in a cell without spontaneous activities. DIC image shows the cell and the probe tip on the PA gel.