A high concentration of collagen induces ADP secretion and TxA2 production in the absence of aggregation.

Wild-type platelets were stimulated with a high level (50 μg/mL) of collagen in the presence or absence of EDTA (5 mM). EDTA inhibited platelet aggregation that 1B5 was unable to prevent in response to a high level of collagen (A). Furthermore, a high level of collagen induced TxA2 production in the absence of aggregation (B). Data were obtained from 3 tests. Bars represent means ± SEM. Since EDTA precludes the measurement of ATP secretion by luciferase assay, dense-granule secretion was evaluated by measuring a loss of mepacrine fluorescence following activation by collagen, using a spectrophotometer as described in “Materials and methods” (C). Blood was drawn from wild-type mice on 3 occasions. Washed platelets were prepared as described and the experiment was repeated 5 times using platelets from each set of mice, for a total of 15 repetitions. The data were pooled. Bars represent means ± SEM.