title: Divalent cation-dependent and independent surface expression of thrombospondin on thrombin-stimulated human platelets.
abstract: Thrombospondin (TSP), a platelet alpha-granule protein, becomes expressed on the surface of thrombin-stimulated platelets. The surface expression of this protein occurs through two distinct mechanisms. At low platelet concentrations (1 X 10(8)/mL), a divalent ion-dependent, low-capacity mechanism predominates. At higher cell concentrations, a divalent ion-dependent, higher capacity mechanism prevails that can account for greater than 90% of all the TSP surface expression measured. This mechanism requires the presence of both calcium and magnesium (Ca + Mg). The dependence of the divalent ion-dependent surface expression on platelet concentration suggests that release of the molecule from the cell followed by its binding to the cell surface mediates this component of the endogenous TSP-platelet interaction. These data are consistent with a two-receptor model for the platelet-surface expression of the endogenous TSP pool.
mesh_terms: D000527:Alprostadil / Q000494:pharmacology; D000911:Antibodies, Monoclonal; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000097:blood; D002413:Cations, Divalent / Q000097:blood; D004492:Edetic Acid / Q000494:pharmacology; D006023:Glycoproteins / Q000097:blood* / Q000276:immunology; D006801:Humans; D008274:Magnesium / Q000097:blood; D011956:Receptors, Cell Surface / Q000378:metabolism; D013806:Theophylline / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology*; D019699:Thrombospondins
chemical_list: D000911:Antibodies, Monoclonal; D002413:Cations, Divalent; D006023:Glycoproteins; D011956:Receptors, Cell Surface; D019699:Thrombospondins; D004492:Edetic Acid; D013806:Theophylline; D013917:Thrombin; D000527:Alprostadil; D008274:Magnesium; D002118:Calcium