Effect of collagen-like substances (C1q, acetylcholinesterase and elastin) on collagen-induced platelet aggregation.

The effects of collagen-like proteins on platelets were studied in human platelet-rich plasmas. The C1q subcomponent of complement (human), acetylcholinesterase (electric eel), and elastin (bovine) had no platelet aggregating activity, despite compositional homologies with collagen in terms of hydroxyproline, hydroxylysine, proline and glycine contents. Upon preincubation with platelets, acetylcholinesterase was incapable of preventing the platelet aggregation triggered by collagen, whereas elastin exerted a weak and inconsistent blocking action. In turn, native C1q strongly inhibited collagen-induced platelet aggregation and 'aggregated' C1q, obtained by ultracentrifugation of freeze-thawed monomeric C1q, had a potentiating effect. These findings confirm the highly specific character of the platelet action of C1q.