Differential degranulation, integrin activation, and calcium flux of young platelets compared with older platelets. Younger (<24 hours old) platelets express higher levels of P-selectin (A) but lower levels of active GPIIb/IIIa (B) in response to PAR4-specific stimulation compared with corresponding older platelets in the same sample. Younger platelets have a greater calcium flux (measured as area under the curve [AUC]) in response to PAR4-specific stimulation (C) and ionomycin (D) (n = 5). (C) Data are individual replicates or mean ± SEM. ∗∗P < .01, ∗∗∗P < .001 by paired t test as indicated. ns, not significant.