Fig. 5. Differential regulation of SRF and NFAT by Ca²⁺. (A) SRF (solid diamonds) or NFAT (open circles) transcriptional activity was determined in WT DT40 cells stimulated with the indicated concentrations of ionomycin along with 5 ng/ml PMA. (B) CN is a downstream effector of Ca²⁺ in the regulation of SRF by BCR signaling. SRF or NFAT transcriptional activity was determined in WT DT40 cells pre-treated with the indicated concentrations of the CN inhibitor CsA prior to stimulation with anti-IgM. The activity of the non-stimulated and anti-IgM stimulated cells were set as 0 and 100% activation respectively. (C) SRF transcriptional activity was determined in IP₃R^–/– DT40 cells pre-treated with 400 nM CsA prior to stimulation with anti-IgM. (D) SRF transcriptional activity was determined in IP₃R^–/– DT40 cells transfected with 15 µg empty vector or 10 or 15 µg CN-A and stimulated with 5 ng/ml PMA.