Depletion of Intracellular Ca2+ by Caffeine and Ryanodine Induces Apoptosis of Chinese Hamster Ovary Cells Transfected with Ryanodine Receptor*

Recent studies have suggested a central role for Ca2+ in the signaling pathway of apoptosis and certain anti-apoptotic effects of Bcl-2 family of proteins have been attributed to changes in intracellular Ca2+ homeostasis. Here we report that depletion of Ca2+ from endoplasmic reticulum (ER) leads to apoptosis in Chinese hamster ovary cells. Stable expression of ryanodine receptor (RyR) in these cells enables rapid and reversible changes of both cytosolic Ca2+ and ER Ca2+ content via activation of the RyR/Ca2+release channel by caffeine and ryanodine. Sustained depletion of the ER Ca2+ store leads to apoptosis in Chinese hamster ovary cells, whereas co-expression of Bcl-xL and RyR in these cells prevents apoptotic cell death but not necrotic cell death. The anti-apoptotic effect of Bcl-xL does not correlate with changes in either the Ca2+ release process from the ER or the capacitative Ca2+ entry through the plasma membrane. The data suggest that Bcl-xL likely prevents apoptosis of cells at a stage downstream of ER Ca2+ release and capacitative Ca2+entry.