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. 2014 Mar;143(3):325–343. doi: 10.1085/jgp.201311108

Figure 4.

Figure 4.

Voltage dependence of blockade of STIM1- and 2-APB–gated Orai3 channels by extracellular Ca2+. (A–C) Effects of extracellular Ca2+o on Na+ currents during voltage steps in WT (A and B) or E85A/D87A/E89A mutant (C) Orai3 channels gated by STIM1 or 2-APB. Hyperpolarizing voltage steps from –120 to +100 mV of 50-ms duration were applied from the holding potential (we used holding of +50 mV for STIM1-gated currents and −30 mV for 2-APB–gated currents). Block was induced by either 20 µM Ca2+ (STIM1- and 2-APB–gated WT Orai3) or 80 µM (triple mutant). (D) Voltage dependence of Ca2+o block. Block was quantified from the ratio of the steady-state currents at the end of the 50-ms voltage steps in control and in the presence of extracellular Ca2+o. The dashed line in each case is a least-squares fit to the Guo and Lu (2000) model (see Materials and methods) with the following key parameters: STIM1-activated Orai3 currents: Z1 = 0.54, K1 = 187 µM; 2-APB–activated Orai3: Z1 = 3.39, K1 = 4523 µM; 2-APB–gated E85A/D87A/E89A triple mutant: Z1 = 0.78, K1 = 9.5 µM. Error bars represent SEM.