Mechanics Regulates ATP-Stimulated Calcium Response in Fibroblast Cells

Cells constantly sense their chemical and mechanical environment. Here we study the effect of mechanics on the ATP-induced calcium response of fibroblast cells in experiments that mimic various tissue environments. We find that in two-dimensional configurations, closely packed cell colonies cultured on a soft polyacrylamide gel (elastic modulus E = 690 Pa) have more cells exhibiting calcium oscillations than colonies on a rigid substrate (E = 36000 Pa). Cells on soft substrates also show a higher number of oscillations following a stimulation, with a slower decay of calcium level relative to those on rigid substrates. Inhibition of gap junctions results in a decrease of the oscillation period and reduced correlation of calcium responses, which suggests additional complexity of signaling upon cell-to-cell contact. Moreover, the frequency of calcium oscillations is independent of the rigidity of the substrate but depends on ATP concentration and cell-cell contact. In additional experiments with cells embedded in a three-dimensional hydrogel matrix, where cell-to-cell contact is absent, more calcium responses are observed when cells are encapsulated in a softer hydrogel (E = 85 Pa). When cell contractility is obstructed by inhibition of myosin, we observe less responsive and fewer oscillating cells. Overall, our observations highlight the influence of mechanical environment on chemical sensing in fibroblast cell colonies.