Figure 1. Human platelets adhere to immobilized laminin and collagen, but spread with different morphology.

(A) Visualization of platelets bound to immobilized matrix proteins. Washed human platelets resuspended at 1 × 10⁸/mL in 2 mM MgCl₂ and 0.5 mM CaCl₂ were seeded on surfaces pre-coated with either human placental laminin 511 or soluble calf-skin collagen. After 30 minutes at 37°C, unbound platelets were removed, adherent platelets fixed with 3% paraformaldehyde, and visualized using Hoffman modulation contrast. Results shown are representative of three separate experiments. Note that platelets bind well to immobilized laminin, but do not spread as well as they do on immobilized collagen. (B) Quantitation of platelet adhesion to immobilized matrix proteins. Washed human platelets were loaded with Calcein AM and seeded onto microtiter wells that had been pre-coated with the indicated concentrations of human laminin or collagen. After a 60 minute incubation at 37°C, the percentage of adherent platelets was calculated by taking fluorescence measurements both before and after removal of unbound platelets. Data shown represents mean values ± SEM from three independent experiments performed using triplicate wells.