Figure 4. Store-operated Ca²⁺ influx is significantly reduced but not entirely abolished in CRACM1-/- mast cells.

(a) Calcium influx measured in response to FcεRI aggregation with 25ng/ml of DNP-HSA in cells pre-loaded with anti-DNP IgE (0.5μg/ml) (representative of 3 experiments). Mast cells derived from CRACM1 +/+ (thick black), +/- (thick grey), -/- (thin black) were loaded with Fura-2AM, re-suspended in a zero calcium buffer ([Ca²⁺]_o) and stimulated as shown. (b) Fura-5F-loaded mast cells were treated with 2 μm thapsigargin (TG) under nominally-Ca²⁺-free conditions for 10 minutes after which extracellular Ca²⁺ ([Ca²⁺]_o) was restored to 1mM to observe Ca²⁺-entry (mean of 3 experiments). The peak Ca²⁺-entry response (ΔRatio =peak ratio-basal ratio) and the maximal rate of Ca²⁺ entry (Ratio units/sec) for each mast cell population were calculated and presented in (c) and (d) respectively (mean ± SEM of 3 experiments). (e) Using the same protocol as in (b), the effects of 1 μm Gd³⁺ (e; mean of 4 experiments) and 30 μm 2-APB (f; mean of 3 experiments) on thapsigargin-activated Ca²⁺ influx were observed on wild type +/+ and CRACM1 -/- primary mast cells.