ID_STIM and Orai1 W76 act in concert to enable full-strength CDI. All currents were recorded as described in Fig. 1 with 20 mM Ca²⁺_o and the standard 10 mM EGTA internal solution. The brackets indicate overlapping mutant cycles. Cells coexpressed the indicated STIM1 and Orai1 variants, and where a label is absent the WT STIM1 or Orai1 protein was expressed. Bars above traces indicate the native CDI elements present in each condition. (A) Representative currents for WT STIM1 + WT Orai1 (from Fig. 1 A) and WT STIM1 + Orai1 W76A (from Fig. 5 B in Mullins et al., 2016). (B) Representative currents for STIM1 3A + WT Orai1 (from Fig. 2 I) and STIM1 3A + Orai1 W76A. (C) Representative currents for STIM1_1–469 + WT Orai1 (from Fig. 1 A) and STIM1_1–469 + Orai1 W76A. (D and E) Summary of the extent of CDI measured for the mutant cycles involving STIM1 3A and STIM1_1–469, respectively. Each point on the summary graphs represents the mean ± SEM for n = 5–6 cells. The residual inactivation persists even when mutant STIM1 and mutant Orai1 are expressed together.