Figure 2.

Ca²⁺ homeostasis in the lumen of the ER (A) and of the Golgi apparatus (B) in control and Bcl-2–overexpressing HeLa cells. Parallel batches of HeLa cells were either cotransfected with the appropriate AEQ chimera (erAEQ and GoAEQ for monitoring the lumen of the ER and of the Golgi apparatus, respectively) and Bcl-2 (Bcl-2), or transfected with the AEQ chimera alone (control). 36 h after transfection, the organelles were depleted of Ca²⁺ to optimize AEQ reconstitution. After reconstitution, the cells were transferred to the luminometer chamber and AEQ luminescence was collected and calibrated into [Ca²⁺] values. Where indicated, the cells were stimulated with 100 μM ATP. All other conditions are as in Fig. 1.