Calcium signaling of chondrocytes under osmotic stress and mechanical stimulation

Chondrocytes play a critical role in cartilage remodeling by mediating the biosynthesis, organization, and modification of extracellular matrix (ECM). They are highly sensitive to the surrounding mechanical and osmotic environments. One of the earliest responses of chondrocytes to stimuli is a transient oscillation in intracellular Ca²⁺ concentration ([Ca²⁺]_i). The major objective of this study was to investigate and compare the Ca²⁺ signaling of chondrocytes, including both primary cells and chondrogenic cell line, under mechanical stimulus and osmotic stress. The roles of seven essential pathways in Ca²⁺ signaling were further examined. Cells were stained with calcium indicator and monitored under confocal microscopy. The results suggested that i) the two types of cells have different calcium signaling mechanisms; ii) mechanical stimulation and osmotic stress employ different mechanisms to initiate calcium responses; iii) osmotic stress could be the major regulation mechanism on the metabolisms of chondrocytes in daily activities.