Figure 3. STIM1 modulates the ion selectivity of the constitutively active V102C Orai1 channels.

A, current–voltage relationships of currents produced by WT Orai1 + STIM1, V102C Orai1 alone, and V102C Orai1 + STIM1 in 20 mm Ca²⁺ or divalent-free (DVF) Ringer solutions. The red arrows indicate the reversal potentials in each case. B, summary of reversal potentials (V_rev) of V102C Orai1 currents in the presence and absence of STIM1. C, currents elicited by replacing the standard extracellular Ringer solution with Na⁺- or Cs⁺-based DVF solutions in V102C Orai1 channels expressed either alone or together with STIM1. In the absence of STIM1, large Cs⁺ currents are seen in V102C Orai1 channels. By contrast very little Cs⁺ conduction is observed in the presence of STIM1 (adapted from McNally et al. 2012).