FIG. 7.
Sequential activation of Rap1. (A) Schematic representation of activation and inactivation of Rap1 in platelets stimulated with α-thrombin under aggregating (solid line) and nonaggregating (dashed line) conditions; approximate time scale in minutes. (B) Model of the sequential regulation of Rap1 activity. α-Thrombin-induced Rap1 activation is initiated by a intracellular calcium generated through PLC activity (arrow 1). A second phase of activity requires PKC (arrow 2) and, in part, integrin αIIbβ3 (arrow 3). Inactivation of Rap1 correlates with the translocation of Rap1 to the Triton X-100, cytoskeletal fraction. Both translocation and Rap1 downregulation require platelet aggregation.