Figure 2. Ionomycin but not IP₃ activates I_CRAC in the absence of IP>₃ receptors.

(A) Average CRAC currents in T0 DT40 cells in response to 1 μM IP₃ (open squares, n = 5), 20 μM IP₃ (filled squares, n = 3) and 1 μM IP₃ plus stimulation for 2 s with 2 μM ionomycin in Ca²⁺-free saline as indicated by the arrow (filled circles, n = 5). [Ca²⁺]_i was clamped to 150 nM. Data were analyzed as in Fig. 1A. (B) Average I/V curves of I_CRAC extracted from representative T0 cells at 300 s and obtained after application of ionomycin (n = 3). (C) Average Ca²⁺ release responses evoked by perfusion of wild type (black, n = 5), T1 (red, n = 4), T2 (green, n = 4) and T3 (blue, n = 4) DT40 with 10 μM IP₃ in combined patch- and balanced Fura-2 experiments (see methods). Baseline of traces was adjusted to T2 DT40 for clarity (50 nM to 130 nM). Arrow indicates time of whole-cell break-in. Cells were kept in regular Ca²⁺-containing solution but were superfused with a Ca²⁺-free saline before whole-cell break-in and throughout the experiment.