Induction of ER stress by IXA4 increases the mobilization of platelet calcium in the Endo-chip laser-injury model. (A) Blood was incubated with vehicle (dimethyl sulfoxide) or the inositol-requiring enzyme 1 activator IXA4 (300 μM) for 2 hours at RT. Blood was then labeled with the calcium dye Cal520 and anti-CD42a, recalcified with CaCl₂ (10 mM), and then immediately perfused through the Endo-chip at 100 s^–1, followed by a laser pulse to the endothelial layer. Representative images of calcium (red) and platelet (CD42a, red) accumulation at the injury site at 10 minutes. (B) Kinetics of calcium (left panel) and platelet (right panel) surface area coverage over time in response to vehicle or IXA4. (C) Calcium (upper panel) and platelet (lower panel) AUC after treatment of blood with vehicle or IXA4. Mean ± SD, n = 3 independent experiments, paired t test. AUC, area under the curve.