On the susceptibility of human platelets to aggregation by concanavalin A and the effect of this lectin on their response to ADP.
Concanavalin A aggregated gel-filtered platelets in 0.9% NaCl solution signifying cross-bridging by the lectin. Aggregation of these platelets by concanavalin A was temperature dependent; it did not occur at 0-4 degrees C unless the platelets were previously trypsinized. The level of aggregation of trypsinized platelets by concanavalin A at 0-4 degrees C was similar to that of untreated platelets at 37 degrees C. It is suggested that trypsin facilitates platelet aggregation by concanavalin A at 0-4 degrees C by causing a configurational change in membrane glycoproteins which orientates concanavalin A receptor sites into positions that favour lectin cross-bridging. Concanavalin A failed to aggregate platelets in plasma. Radioisotope studies showed that the amount of [3H]concanavalin A which combined with platelets in plasma was extremely low compared with gel-filtered platelets in saline. The aggregation of Ehrlich ascites cells by concanavalin A was considerably reduced when platelet-free plasma was added to the medium suggesting that it was due to the presence of concanavalin A-reactive components in the plasma. Concanavalin A inhibited the ADP-induced aggregation of platelets suspended in plasma or in a salts solution supplemented with calcium and fibrinogen, although the inhibitory effect was more conspicuous in the latter case. The results suggests that concanavalin A produces its inhibitory effect on ADP-induced platelet aggregation by interacting with membrane glycoproteins, and this further suggests their involvement in aggregation.
D000244:Adenosine Diphosphate / Q000494:pharmacology*; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D003208:Concanavalin A / Q000494:pharmacology*; D005340:Fibrinogen / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D013696:Temperature; D014357:Trypsin
D003208:Concanavalin A; D000244:Adenosine Diphosphate; D005340:Fibrinogen; D014357:Trypsin; D002118:Calcium