Residual inactivation in the absence of ID_STIM remains Ca²⁺-sensitive. All currents were recorded in HEK293H cells cotransfected with WT Orai1-GFP together with either WT mCh-STIM1 (aa 1–685) or mCh-STIM1_1-469 after induction of I_CRAC reached a maximum (∼300 s after break-in). Currents were evoked by 200-ms hyperpolarizations to the voltages indicated. (A) Representative currents are shown with the STIM1 variant and extracellular [Ca²⁺] and intracellular [EGTA] or [BAPTA] indicated in mM. WT traces are from Fig. 3 A in Mullins et al. (2016). (B) The extent of CRAC channel inactivation for the various conditions, summarized as current remaining at the end of the pulse. Each point represents the mean ± SEM for n = 5–6 cells. (C) Current during 100-ms steps from +30 to −100 mV was recorded from a representative cell expressing STIM1_1–469 + WT Orai1, first in 20 mM Ca²⁺_o and then in divalent-free (DVF) extracellular solution.