DAF fluorescence intensity in fluorimetric assay: specificity for NO in human and mice platelets. (A) DAF-FM–loaded washed platelets in suspension were incubated with either SNAP (100 µM) or H₂O₂ (100 µM) (*P < .01 vs control and H₂O₂). (B) DAF-FM–loaded platelets were stimulated with collagen (50 µg/mL) after preincubation with vehicle (control), l-arginine, L-NIO, L-NMMA, D-NMMA, cPTIO, BAPTA, or EGTA, and the DAF-FM fluorescence intensity was recorded (^#P < .005 vs unstimulated; *outside the column P < .0001 vs l-Arg; *inside the column P < .005 vs vehicle). (C) DAF-FM–loaded washed platelets from wild-type (white columns) or eNOS^−/− (gray columns) mice were stimulated with collagen after preincubation with vehicle (control) or with the eNOS substrate l-Arg, 100 μM (^#P < .001 vs l-Arg–treated wild-type; ^§P < .001 vs wild-type).