Malignant T cells express different numbers of Ca²⁺ channels than normal T cells. (A-C) Effects of nifedipine on blocking intracellular Ca²⁺ release in malignant and normal T cells. Human peripheral blood T cells (A), Jurkat (B), and CEM (C) T cells were loaded with 1 μM Fluo-4 in PBS (without extracellular Ca²⁺) and preincubated with 100 to 300 μM nifedipine for 10 minutes. Cells were then stimulated with 0.5 μM ionomycin to induce the intracellular Ca²⁺ release. (D-F) Effects of Bay K 8644 on induction of intracellular Ca²⁺ release in malignant and normal T cells. Human peripheral blood T cells (D), Jurkat (E), and CEM (F) T cells were loaded with 1 μM Indol-1 and pretreated with or without nifedipine for 10 minutes and then stimulated with 100 μM Bay K 8644. The intracellular Ca²⁺ release was monitored by FACS. Results are representative of 3 independent experiments.