Orai1-GCaMP6f current and fluorescence in response to changes in membrane potential and external Ca²⁺. (A and B) Whole-cell currents (A) and Orai1-GCaMP6f fluorescence (B) in response to a series of steps to increasingly negative membrane potential in 2 mM external Ca²⁺. Membrane potentials are indicated above the traces. Data from three different cells. (C and D) Plots of Orai1-GCaMP6f whole-cell current (C) and fluorescence (D) for the same three cells as a function of test potential in 2 mM external Ca²⁺. (E and F) Scatterplots of whole-cell current versus fluorescence (colored diamonds) for the same three cells with fitting to the Hill equation (gray line; R² = 0.992 and hc = 1.6 with 95% CI of 1.2–2.2). (F) Enlargement of lower central portion of E. (G and H) Plots of Orai1-GCaMP6f whole-cell current (G) and fluorescence (H) in response to a series of 600 ms duration −100 mV test pulses at increasing external Ca²⁺ concentrations. External Ca²⁺ concentration in mM are indicated beside the traces. G and H correspond to cell E (see Fig. S3). AU, arbitrary unit.