Mechanisms of platelet adhesion to the basal lamina

The human glomerular basal lamina (HGBL) is composed of collagenous and noncollagenous glycoproteins. We assessed the role played by each costituent in platelet-basal-lamina interaction by selective cleavage and removal of each component by clostridial collagenase or by pepsin. When noncollagenous proteins are removed from HGBL, human platelets exhibit littel reactivity toward the residual collagen framework of the isolated basal lamina. With the noncollagen matrix of basal lamina, after removal of the bulk of the collagen, platelet adhesion and spreading proceed normally in the presence of divalent cations, similar to what occurs on intact basal lamina. No platelet degranulation or aggregation is observed. The results indicate that the basal lamina collagen, even in its native packing arrangement, lacks affinity for platelet adhesion and is incapable of triggering platelet release reactions. Platelet adhesion and spreading on the basal lamina appears to depend primarily on the presence of the noncollagen components and to require divalent cations. The data suggest the presence on platelets of receptors for basal lamina distinct from those for interstitial collagens. These receptors activate a unique modulation of platelet behavior, ie, adhesion and spreading without degranulation. A difference in biologic function of the basal lamina and interstitial collagens is apparent in these experiments.