Fig. 5. Refilling of Ca²⁺ stores after agonist stimulation in control (A), PMCA- (B) and SERCA- (C) overexpressing CHO cells. Ca²⁺ depletion, aequorin reconstitution and Ca²⁺ refilling were carried out as in Figure 3, except that KRB was supplemented with 100 µM CaCl₂ instead of 1 mM. After a steady-state [Ca²⁺] level was reached, the cells were challenged, where indicated, with 100 µM ATP.