Characteristics of the major platelet membrane site used in binding to collagen.

Abstract Meyer and Weisman (1) showed that the adhesion of washed rabbit platelets to soluble collagen adsorbed to glass is inhibited by the presence of soluble proline/hydroxyproline-rich materials in the platelet suspension suggesting that there are sites on the platelet that recognize the high content of these two amino acids on the surface of collagen in its triple helical state. It is now found that similar inhibition can be obtained on a collagen fiber surface using human as well as rabbit platelets in platelet-rich plasma (PRP) or in various washed platelet suspensions. Using polyhydroxyproline (PHP) and rabbit platelets it could be shown that the action of PHP is on the platelet membrane since inhibition occurs almost immediately and is also seen when fixed platelets are used. Inhibition is still seen when free PHP is removed from the platelet suspension. The inhibitory effect of PHP is specific to collagen and was not seen for platelet adhesion to albumin- or globulin-coated surface. We have shown earlier that non-aggregating concentrations of ADP inhibit platelet adhesion as a result of binding to the platelet membrane but independent of the induced shape change (2). PHP action, however, differs from that of ADP since no time lag occurs and it is not blocked by AMP. Furthermore, PHP does not induce a shape change. Therefore, ADP release cannot have occurred. A maximum of inhibition of adhesion by PHP of ∼60±10% was similar to that given by ADP. However, addition of both agents together did not produce greater inhibition than either alone. This suggests that the same site is affected but that ADP action on the platelet surface is not direct but operates through a delayed lodal interaction mechanism. This indirect action of ADP probably also affects binding sites to other surfaces since adhesion to albumin- and globulin-coated surfaces is also reduced by ADP.