Fig. 4. Knockdown of STIM1 with siRNA inhibits SOCE without depleting the ER Ca²⁺ store.

a A representative western blot of six independent experiments showing the expression level of STIM1 in mock-transfected SU-DHL-4 cells, or cells transfected with scrambled siRNA or with siRNA against STIM1. The expression level of GAPDH was used as loading control. b Quantification of the STIM1/GAPDH protein levels of six independent experiments relative to the level in mock-transfected SU-DHL-4 cells, which was set at 1. c Analysis of Ca²⁺ influx after store depletion in transfected SU-DHL-4 cells using the ratiometric Ca²⁺ indicator Fura-2 AM. To deplete the ER Ca²⁺ store, 3 mM EGTA and 1 µM TG were added as indicated. After store depletion, Ca²⁺ influx was triggered by adding 10 mM CaCl₂. The curves represent the mean ± SEM of three independent experiments. Quantification of the Ca²⁺ influx is provided as the peak amplitude (∆ F₃₄₀/F₃₈₀) in d, whereas the TG-releasable Ca²⁺ is quantified as the AUC (F₃₄₀/F₃₈₀ × s) in e. In the dot plots, data are represented as the mean ± SEM of at least three independent experiments. Statistically significant differences were determined with a one-way ANOVA (*p < 0.05, ***p < 0.001). NS not significant.