Frozen and freeze dried human blood platelets remain intact morphologically when preserved by cryoprotective agents. These studies have investigated effects of 1) the release reaction, 2) discoid stabilization by CB, and 3) N on platelet morphology in FD specimens. Platelets were collected in 1/10 volume of acid citrate and platelet rich plasma (PRP) obtained by centrifugation. Aggregating agents (adenosine diphosphate, 2 × 10-6 M, epinephrine, 5 × 10-5 M, collagen, 30 μg/ml, thrombin 0.2 U/ml) CB (25 μg/ml), trypsin (3 mgs/ml), and N (20 U/ml), then cryoprotective agents, were added. Platelets were FD and the ultrastructure examined. Aggregating agents were associated with 1 ) the appearance of amorphous electron dense material within platelets extending via channels to the exterior; 2) membranous complexes contiguous to plasma membranes; 3) numerous organelles adjacent to the plasma membrane. Platelets in artificial thrombi also showed homogeneous electron opaque areas and membrane rich surface complexes. CB caused vacuolization and previously reported concentric membranous structures were noted in trypsinized platelets. N did not prevent interplatelet bridging. In conclusion, aggregated FD platelets differ from platelets fixed by traditional means, providing morphologic support that platelet organelles and membrane systems relate structurally to the platelet exterior as well as the canalicular system to provide a catalytic lipoprotein surface during the release reaction.
The synthetic RGDS peptide inhibits the binding of fibrinogen lacking intact alpha chain carboxyterminal sequences to human blood platelets