Platelet adhesion to noncovalently immobilized collagen

Affinity chromatography with collagen covalently immobilized to agarose is frequently used to measure platelet adhesion. A simpler, equally sensitive affinity chromatographic assay for quantitation of platelet adhesion to noncovalently immobilized type I collagen has been developed. In the presence of EDTA, human and canine platelet adhesion increased linearly with increasing collagen up to 0.3 mg/ml of packed resin and attained a maximum of 90% adhesion above 1 mg/ml. No temperature dependence was observed. When collagen fibrils were immobilized with periodate-oxidized or CNBr-activated agarose, platelets from both species were rarely observed adhering to fibrils in close association with the agarose surface. Increased divalent cation levels resulted in increased platelet adhesion. In citrated platelet-rich plasma, where aggregation may occur, experiments with thrombopathic canine platelets which fail to aggregate or secrete in response to collagen suggest that up to 84% of the maximal "adhesion" observed in citrated systems is adhesion to collagen per se. In contrast to adhesion to glass bead surfaces, in vitro platelet adhesion to collagen was only marginally affected in the absence of aggregation and secretion. Normal platelet interaction with fibrinogen is not essential for platelet adhesion to collagen. Formalin fixation had no effect on platelet adhesion to collagen. Fixed platelets were quantitatively recovered after elution with 1M NaCl. Our results suggest that in vitro adhesion of canine platelets to collagen is similar to that observed for human platelets and that collagen fibril-fibril associations may be essential for platelet adhesion whereas active platelet metabolism and membrane fluidity are not. Initial adhesion of platelets to collagen in vitro appears to be predominantly ionic in nature.