Figure 4.

Bcl-2 prevents ER Ca²⁺ pool depletion. WEHI7.2 cells (A–D) and W.Hb12 cells (E–H) were incubated for 3 h (A, B, E, and F) or 18 h (C, D, G, and H) in medium with a Ca²⁺ concentration of 1.3 mM (A, C, E, and G) or medium with a Ca²⁺ concentration of 0.13 mM (B, D, F, and H) and then loaded with Fura2-AM. Shown are continuous fluorometric tracings in which addition of 100 nM TG (right hand arrow) induces an increase in cytosolic Ca²⁺ concentration. Note that EGTA (left hand arrow) was added immediately before TG to chelate extracellular Ca²⁺; hence, the increase in cytosolic Ca²⁺ that follows TG addition represents release of Ca²⁺ from the ER pool. Large vertical oscillations in fluorescence near the beginning of each tracing correspond to brief light exposure during EGTA and TG additions.