Effects of disruption of the actin cytoskeleton on α-granule and dense granule secretion. (A) Platelets were incubated in the presence of either vehicle (•), 4 μM cytochalasin E (○), or 4 μM latrunculin A (▪) for 20 minutes. Platelets were then stimulated with 100 μM SFLLRN and subsequently fixed with paraformaldehyde at the indicated times. Samples were assayed for P-selectin expression by flow cytometry to monitor α-granule secretion. (B) Platelets were incubated in the presence of either vehicle (•), 4 μM cytochalasin E (○), or 4 μM latrunculin A (▪) for 20 minutes. Platelets were then stimulated with 0.2 μM PMA for the indicated times, fixed with paraformaldehyde, and assayed for P-selectin expression. (C) Platelets were incubated in the presence of either vehicle (•), 4 μM cytochalasin E (○), or 4 μM latrunculin A (▪) for 20 minutes. Platelets were then stimulated with 100 μM SFLLRN and assayed for ATP release using a luciferin-luciferase detection system to monitor dense granule release. (D) Platelets were incubated in the presence of either vehicle (•), 4 μM cytochalasin E (○), or 4 μM latrunculin A (▪) for 20 minutes. Platelets were then stimulated with 0.2 μM PMA and assayed for ATP release.