FIGURE 2.

Biophysical properties of STIM1 DQ-mediated Orai1 currents. A, average CD over time recorded from cells expressing Orai1 and STIM1 WT (black) or STIM1 DQ (red) extracted at +80 and −140 mV. Solution changes are indicated. B, averaged maximal inward CD for currents recorded in A in the different indicated external solutions. C, for noise analysis, currents were extracted at −120 mV in 2 mm [Ca²⁺] bath or in either DVF or in Mg²⁺-free bath with the indicated added [Ca²⁺]. D, current variance was extracted at indicated (red) time points in C and plotted against the CD. The red line indicates the fit using a parabolic function. E, number of channels as extracted from the maximum of the fit in D. F, single channel current (SCC) as extracted from the initial slope indicated in D. G, apparent measured open probability (P_o) of Orai1 channels as a function of the applied voltage. The cells were held at 0 mV in a 2 mm Ca²⁺-containing solution and steps of 20 mV were applied from −160 to +80 mV over 100 ms followed by a step voltage to −100 mV. Boltzman equation was used to normalize the maximum tail current after each voltage step (see “Experimental Procedures”).