Studies On The Mechanism Of Platelet Adhesion To Collagen- Sepharose

Abstract

Platelet interaction with the collagenous material of damaged vessel walls is one of the primary events leading to cardiovascular disease. In vitro methods and known antiplatelet agents were employed in order to better understand the adhesion and release processes. These processes were quantitated using 51Cr and l4c-serotonin labeled rabbit gel filtered platelets (GFP) and immobilized collagen. Metabolic inhibitors, antimycin-A and 2-deoxyglucose, partially reduced adhesion (45%) while addition of 0.1% glucose reversed their effect. Scanning electron microscope studies indicated that energy depleted GFP bound less tightly to collagen fibers and remained disc shaped. These and other studies concluded that the adhesion process consisted of an energy dependent phase. Membrane active compounds such as the phenylthiazines strongly inhibit adhesion (>70%) at concentrations up to 0.1 mM. Their activity was related to their ability to penetrate the membrane’s lipid layers. Verapamil, a Ca++ channel blocker, was inactive. ADP receptor antagonists affected both adhesion and release to varying degrees. Phosphodiesterase inhibitors and adenyl cyclase activators were most effective in combination in reducing release (>70%) but weak in reducing adhesion (<22%). Studies with 13-azaprostanoic acid (13-AZA), a thromboxane-A2 antagonist (TXA2), indicated that TxA2 generation had very little effect on adhesion or release from adhering platelets. Sulfhydryl modifying agents were effective in reducing both adhesion (>59%) and release (>57%). This report concludes that the platelet-collagen interaction was a multi-component process modified by small organic molecules. Furthermore, it was demonstrated that the release process of adhering platelets was independent of the adhesion process initiated by collagen.