FIGURE 3.

C terminus of STIM1 is sufficient to pre-activate Orai1-induced Ca²⁺ influx and CRAC current. A-D, C-STIM1 raises the resting Ca²⁺ level in Jurkat T cells by opening CRAC channels. Solution exchanges are indicated. Vertical lines indicate the time of solution exchange. Averaged [Ca²⁺]_i responses (±S.E.) in control (GFP only) Jurkat cells (A, n = 9 cells), Jurkat cells overexpressing full-length STIM1 (B, n = 9), and the C-terminal portion of STIM1 (C-STIM1) (C, n = 21). D, resting [Ca²⁺]_i in Jurkat cells (from left to right: n = 11, n = 17, and n = 313). E, time course of inward current at -100 mV in a representative HEK cell overexpressing C-STIM1 and wild-type Orai1. Ca²⁺-free internal solution. Solution exchanges are indicated. F, I-V curves for indicated external solutions. G, current density determined in 2 mm external Ca²⁺ for 1) control HEK cells transfected with GFP only (squares), and 2) C-STIM1 + Orai1-overexpressing HEK cells (circles).