Platelet adherence to collagen: role of plasma, ADP, and divalent cations

The effect of varying methods of platelet preparation and the role of ADP and divalent cations in supporting platelet adherence to collagen and the release of 14C-serotonin were assessed by affinity chromatography on collagen/Sepharose to define physiological conditions for this interaction. Platelets were separated by centrifugation or gel filtration from blood anticoagulated with EDTA or citrate and suspended in native plasma or buffer. After labelling with 51Cr or 14C-serotonin, they were passed though columns of collagen covalently linked to cyanogen bromide-activated Sepharose. Adherence to collagen was less in plasma as compared to buffer, was increased by centrifuging the platelets before testing, and was unaltered by addition of ADP. Removal of ADP with CP/CPK decreased the adherence of gel-filtered citrated and EDTA platelets and washed EDTA platelets (P less than 0.001) but not EDTA platelets in plasma. Adherence and release of citrated platelets in plasma or buffer containing CP/CPK were greater than that of EDTA platelets (P less than 0.01); no difference existed with gel-filtered platelets. The addition of 1 mM Mg++ to citrate or EDTA-anticoagulated washed platelets increased adherence and release (P less than 0.01). The results indicate that the choice of experimental conditions affect the assessment of factors which influence or promote platelet interaction with collagen. Platelet-collagen adherence is enhanced by laboratory manipulations and partially inhibited by normal plasma. Maximal adherence and release occur when divalent cations, particularly Mg++, and ADP are available. Their absence reduces but does not inhibit these reactions.