Binding of radiolabelled collagen to blood platelets.

Purified, soluble collagen was prepared from rat skin, and the tyrosine residues were labelled with 125 I by the chloramine T method. The collagen was added to platelet-rich plasma from rats or rabbits, and then layered on 23 % w/v Ficoll. After centrifugation at 3900 g for 20 min, the platelets were recovered from beneath the Ficoll, and the radioactivity associated with them was measured. This represented the platelet-bound collagen, since very little collagen penetrated the Ficoll if platelets were absent. The amount of platelet-bound collagen paralleled the extent of collagen microfibril formation, which in turn increased with the time the collagen was preincubated at 36 °C before being added to the plasma. The amount of binding in each sample was reproducible within groups of rats or rabbits, but the amount of collagen bound per platelet was about 3 times greater in samples from rabbits than from rats.