Platelet shape change induced by the peptide YFLLRNP

Platelet shape change represents an early response to activating agents. Wh ereas the PAR-1-activating peptide SFLLRN induces a total platelet activati on, YFLLRNP brings the process only to the shape change step in a process i ndependent of the cytosolic Ca2+ concentration. In this paper, the YFLLRNP- induced shape change has been observed in human citrated platelet-rich plas ma (PRP). Scanning electron microscopy of platelets activated by 300 muM YF LLRNP showed platelets that had changed shape and extended long pseudopods. The protein content of the material sedimenting at 13,000 x g from 1% Trit on X-100 extracts increased during the shape change, indicating a reorganiz ation of the cytoskeleton. This was supported by electrophoresis. The GP II b-IIIa complex was not activated, however, and the platelets that had under gone shape change did not support clot retraction. As no increase in bindin g of FITC-labeled annexin V (FITC-annexin V) was observed, the extensive sh ape change was not associated with a disturbance of the membrane phospholip id asymmetry. Platelet aggregation was never observed with 300 muM YFLLRNP, but could be seen at much higher concentrations, neither was secretion fro m dense granules observed at 300 muM as no extracellular ATP could be obser ved. These studies confirm and extend the concept of the Ca2+-independent s hape change as a distinct and sharply delineated process that, in itself, m ay be of little pathophysiological importance if such "partly activated" pl atelets occur in the circulation. (C) 2001 Elsevier Science Ltd. All rights reserved.