(A) Illustration of calcium imaging for in situ chondrocytes in a cartilage explant. Half cylindrical cartilage explant (3mm in diameter and 2 mm in thickness) in a glass-slide imaging chamber is mounted on a confocal microscope (Zeiss LSM510) and imaged with 20x objectives. (B) Imaging area is chose to be 200 [.proportional]m below the explant's articular surface and on the center axis of explant. (C) A typical [Ca2+]i intensity oscillation curve of a chondrocyte over 15 minutes and the definitions of spatiotemporal parameters, including the number of [Ca2+]i peaks, magnitude of 1st peak m1, time to 1st peak t1, relaxation time of 1st peak t2, and time interval between two neighboring peaks t3.