Figure 5. STIM2 can regulate Ca²⁺ influx independent of STIM1.

(A) STIM2 expression-mediated increases in basal Ca²⁺ are not affected by knockdown of STIM1. Cells were transfected with YFP-STIM2 ~60 hours after STIM1 or GL3 control siRNA transfection and 9 hours before imaging. Cells selected expressing YFP at background autofluorescence (non transfected) or 4–8 times autofluorescense (transfected). N=15 sites.

(B-C) Experiments showing that STIM2-triggered R-SOC is not affected by STIM1 knockdown and STIM1-triggered R-SOC is not significantly affected by STIM2 knockdown. Ca²⁺ addback experiments were performed in cells prepared and selected as described in (A) expressing STIM2 (B) and STIM1 (C). 9 hour transfection. N=3 wells.

(D-E) Control experiment showing that prolonged overexpression of YFP-STIM2 downregulates the maximal attainable Ca²⁺ influx rate. Influx rates were measured in Ca²⁺ add-back experiments in the presence of thapsigargin. Expression at 9 hours (D) is compared to expression at 24 hours (E). N=4 sites from 2 wells.