Summary
The effect of limited platelet activation, in the absence of aggregation, on the subsequent ability of rabbit platelets to adhere to collagen was studied in vitro. ADP at concentrations that initiate shape change (>0.01. μM) reduce platelet adhesion. Shape change per se however, was not responsible since the time-dependence of the effect of ADP on shape change and adhesion is different and ADP induces reduced adhesion even when shape change is prevented with PGE1 or fixatives. Platelets shape changed without ADP addition, e. g. by chilling or by low ethanol concentrations, display normal adhesion to collagen
It appears likely that upon binding to the platelet ADP induces a time-dependent alteration in the membrane, akin to refractoriness, that influences binding sites for collagen. The effect of ADP can be blocked by prior addition of AMP but not if the additions are reversed. The implications of the present findings for platelet adhesion studies are discussed.
Keywords
Platelets - Collagen - ADP - Adhesion - Cell shape
