FCDI and SCDI of Orai1 current activated by STIM1, SOAR, and STIM1 C-terminal deletion mutants. (a and b) Example traces of FCDI of Orai1 current activated by the indicated STIM1 mutants was measured in pipette solution containing 10 mM EGTA and external solution containing 10 mM Ca²⁺. For fast inactivation, −100 mV step voltage pulse of 1-s duration were applied when the current was fully developed. Table S1 shows the mean of 5–10 experiments similar to those in a and b of time constants (τ₁ and τ₂) obtained by fitting the current traces with double or single exponential functions, whichever was appropriate, and extent of inactivation. Example of double (STIM1) and single (STIM1Δ447–460) exponential fits and the quality of the fits (residuals) are shown in the insets. (c) Normalized averaged whole cell current levels at −100 mV measured in HEK cells expressing Orai1 and the indicated STIM1 C-terminal deletion mutants. Pipette solution contained 1.2 mM EGTA and 10 mM Ca²⁺ was added to the bath at the time indicated, 5 min after establishing the whole cell configuration. Table S1 shows the extent of inactivation in each case. The results are given as mean ± SEM of the number of experiments listed in parentheses.