Immunocytochemical Study on the Redistribution of alphallbbeta3 Integrin and Cytoskeleton adherent to collagen

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Initial contact of platelets with collagen is mediated via alpha2beta1 integrin.alphallbbeta3 is involved in platelet spreading. However, the precise mechanism leading to platelet spreading and firm adhesion on collagen are less understood. We have found by immuno-scanning electron microscopy that the platelets adherent to immobilized collagen secreted fibrinogen which then settled onto the cover soip and worked as an anchorage/ligand for alphallbbeta3 during platelet spreading.Next, we have examined the cytoskeletal patterns in human platelets adherent to collagen using immunofluorescence microscopy. Vinculin was detected as aligned patches, and located along actin filaments. Although talin was not detected at the ends of actin filaments, it was concentrated at the periphey of the platelets where the platelets were in close contact with adjacent platelets. pp125^<FAK> was detected as small spots, all of which, as a whole, formed a ring at the central areas of adherent platelets. These results suggest that the adherent platelets fail to form typical focal adhesion.