Aggregation of gel-filtrated platelets induced by thrombospondin

Thrombospondin (TSP) was purified from bovine platelet-released substances by heparin-sepharose affinity chromatography and gel-filtration. Purified TSP was investigated whether to induce platelet aggregation in order to clarify the role of TSP in platelaet aggregation.TSP induced aggregation of gel-filtrated platelets (GFP) in dose-dependent fashion in the presence of calcium and magnesium ions. The aggregation were dissociated with EDTA. Aminosugars inhibited and dissociated the platelets aggregation by TSP. GFP fixed with formalin were aggregated by TSP in the same manner of GFP. Aggregability of GFP fixed with calcium ions was larger than without calcium ions.These results suggest that TSP may agglutinate native inactive platelets by interbridging the platelets probably by its lectin activity, and this agglutination may need calcium ions not only for TSP but also for the receptor of TSP on the platelet membrane surface.