Figure 2. EF-hand mutant of STIM2 weakly interacts with Orai1.

A and B. Expression of EYFP-STIM1-EF hand mutant (D76N, D78N) induces a constitutive Ca²⁺ entry (A) that is slightly enhanced following thapsigargin treatment (B). C and D. In contrast, expression of EYFP-STIM2-EF hand mutant (D80A) has no effect on basal Ca²⁺ leak (C) and appears to exert an inhibitory effect on thapsigargin-induced Ca²⁺ entry (D). E and F. Co-expressing CFP-Orai1 with EYFP-STIM2-EF hand mutant induces a constitutive Ca²⁺ entry (E) that is slightly enhanced following thapsigargin treatment (F). All plasmid concentrations were 0.5μg per transfection. Data summarized in G (peak Ca²⁺ rise) and H (rate of Ca²⁺ rise) are mean ± SEM for n=4 experiments (A–D) and n=3 (E–F).