Hydrostatic pressure provides an isotropic mechanical stimulus capable of modulating biological equilibria and reaction rates through volumetric effects. To explore how pressure perturbs signaling processes in living cells, HeLa cells were employed as a model system and intracellular Ca2+ dynamics were monitored using Fluo-4 AM under stepwise pressurization and depressurization. Control experiments in buffered solution revealed that Fluo-4 AM fluorescence decreases monotonically with increasing pressure due to pressure-promoted Ca2+ dissociation, while DAPI, used as an in situ indicator of cell viability, showed negligible pressure dependence. In contrast, cell suspensions exhibited a distinct response. Pressurization produced little immediate change, whereas depressurization triggered rapid and reproducible increases in Fluo-4 AM fluorescence, indicative of transient cytosolic Ca2+ elevations. Time-resolved traces showed gradual decay of this signal, reflecting cellular homeostatic mechanisms such as Ca2+ resequestration or efflux. Pharmacological depletion of endoplasmic reticulum stores with thapsigargin attenuated but did not abolish depressurization-induced responses, and removal of extracellular Ca2+ via EGTA did not suppress the fluorescence increase. These findings implicate intracellular Ca2+ release as the primary source of the pressure-regulated signal. Furthermore, this study demonstrates that hydrostatic pressure offers a quantitative means to modulate intracellular signaling pathways and establishes a foundation for mechanistic studies of mechanotransduction in living cells.