Orai1 regulates Ca²⁺-dependent platelet responses. (A) Integrin activation and granule release. WT and Orai1^R93W platelets were stimulated for 10 minutes with the indicated agonists, stained for expression of activated αIIbβ3 or P-selectin, and immediately analyzed (n = 5-6). (B) αIIbβ3-dependent platelet aggregation (results are representative of 3 independent experiments). (C) PS exposure on platelets adherent to collagen under flow. WT and Orai1^R93W whole blood was perfused over collagen at a shear rate of 1000 s⁻¹ for 2 minutes, and stained with annexin V–Alexa 488 and anti-GPIbα-Alexa 594. The surface area covered by platelets and the number of PS-positive cells was evaluated in 6 visual fields from 3 independent experiments. (D) PS exposure on platelets activated under static conditions. Platelets were stimulated with the combination of PAR4p (1 mM) and Cvx (indicated doses) for 10 minutes under static conditions, stained with annexin V–Alexa 488, and immediately analyzed. Results are expressed as mean plus or minus the standard error of the mean (SEM) (n = 7-8). *P < .05, **P < .001, ***P < .0001.