Figure 6

Participation of [Ca²⁺]_i in the apoptotic process. a, Measurement of [Ca²⁺]_i after SC-1 induction: Cells were washed with Ringer solution, and, at Point 1, SC-1 (40 μg/ml) or control antibody chrompure human IgM (40 μg/ml), diluted in Ringer solution, was added. At Point 2, cells were washed with Ringer solution. A 2.7-fold increase in intracellular Ca²⁺ concentration was observed after approximately 50 seconds of induction with SC-1. b, Effect of Ca²⁺-Chelator, 1, 2-bis(2-aminophenoxy)ethane-N, N,N′,N′-tetraacetic acid (BAPTA) on apoptosis: Cells were preincubated for 90 minutes with increasing amounts of BAPTA, followed by incubation with 40 μg/ml of SC-1 for 24 hours. Apoptotic cells were determined using CellDeath ELISA. An increasing amount of BAPTA had no effect on cell survival after induction of SC-1–induced apoptosis. Treatment with increasing amounts of BAPTA without SC-1 did not show any effect. c, Effect of Ca²⁺-Chelator BAPTA on CD55^SC-1 expression: Cell line 23132 was induced with 40 μg/ml of SC-1 in the presence or absence of BAPTA for the periods indicated above, and then membrane lysates and Western blots were prepared and stained with SC-1. Coomassie-stained gels show loading of equal protein concentrations on each lane. A clear increase in CD55^SC-1 expression with different kinetic was visible in both experiments. Staining of additional protein is due to an unspecific cross-reaction with the Ku70 autoantigen as described earlier.