Figure 4.

Ca ²⁺ homeostasis in the ER lumen of control and PKC-overexpressing HeLa cells. Parallel batches of HeLa cells were either cotransfected with erAEQ and a PKC-GFP chimera including the indicated PKC isoform or transfected with erAEQ alone (control). 36 h after transfection, the Ca²⁺ stores were depleted of Ca²⁺ to optimize aequorin reconstitution as detailed in the text. After reconstitution, the cells were transferred to the luminometer chamber, and the ER store was refilled by switching the perfusion medium from KRB/EGTA to KRB/Ca²⁺. Where indicated, the cells were perfused with 1 mM CaCl₂ and challenged with 100 μM histamine.