Adhesion of rat blood platelets to native rat tail collagen fibrils was studied in
the electron microscope under conditions that preserved collagen-associated proteoglycans
(CAPG). The CAPG molecules were aligned in chain-like configurations that encircled
the fibrils with a 65 nm period; they appeared to coat the fibrils completely and
extended 60-100 nm away from the fibril. The initial platelet-fibril contact occurred
between the platelet glycocalyx and the CAPG of the fibrils i.e. between two surfaces
with net-negative charges. When close contact was established between the fibril surface
proper and the platelet membrane, CAPG were not identified in the area of contact,
and the collagen-platelet distance was reduced to a ~10-12 nm wide gap traversed by
delicate links in register with fibril periodicities.
Keywords
Platelets - Collagen - Proteoglycans
