Relationship of the CIB-GPIIb/IIIa complex to platelet granular secretion of ADP. Formation of the CIB-GPIIb/IIIa complex may be necessary for platelet granular secretion of ADP. (A) Confocal images of washed platelets allowed to spread on Fg and stained for F-actin. Ai: Untreated platelets are fully spread. Aii: Apyrase is present during platelet adhesion. Aiv: Apyrase was added to spread platelets. Av: Platelets were allowed to spread in the presence of apyrase. After 45 minutes, platelets were washed free of apyrase and exogenous ADP was added. ADP receptor P2Y12 antagonist, 2MeSAMP (Aiii) or P2Y1 antagonist MRS 2179 (Avi), is present during platelet adhesion to Fg. (B) Confocal images of washed platelets allowed to spread on Fg and stained for F-actin. Bi: Platelets loaded with GPIIb cytoplasmic peptide (GPIIb Pep) showed filopodia. Bii: Exogenous ADP was added to GPIIb Pep-loaded platelets. Biii: Platelets loaded with UN7.79 showed long filopodia. Biv: Exogenous ADP was added to UN7.79-loaded platelets. Original magnification, × 600.