Platelet interaction with the extracellular matrix produced by cultured endothelial cells: a model to study the thrombogenicity of isolated subendothelial basal lamina.

Cultured bovine endothelial cells produce an extensive underlying extracellular matrix (ECM) which closely resemble the vascular subendothelial basal lamina in its organization and chemical composition. This naturally produced ECM was used to study the interaction of platelets with the subendothelium when exposed or covered with vascular endothelial cells. Incubation of platelet rich plasma with the ECM induced a rapid and massive platelet adherence, aggregation, thromboxane formation and release reaction. These were demonstrated using phase and scanning electron microscopy, Indium-111 or (14C)-serotonin labelled platelets, and a radioimmunoassay for thromboxane B2. In contrast to the ECM no platelet activation was induced either by uncoated plastic dishes or ECM covered with a confluent endothelial cell monolayer. Aspirinized platelets failed to undergo aggregation and degranulation, when incubated with the ECM. Culture dishes coated with characteristic constituents of the basal lamina such as collagen type IV and type V or fibronectin induced a much lower platelet reactivity as compared with ECM coated dishes. Digestion of ECM components (collagen, fibronectin, hyaluronic acid, and chondroitin sulphate) by specific enzymes was not associated with a substantial decrease in its platelet reactivity. Furthermore, exposure of ECM to sodium dodecyl sulphate or sodium periodate, or freezing and thawing did not decrease its biological activity. In contrast, platelet activation was completely abolished following heat denaturation or glutaraldehyde fixation of the ECM. The availability of a naturally produced ECM provides an appropriate model to study the interaction of platelets with the subendothelium in a controlled system which is isolated from other components of the vessel wall.