Platelet release reaction and aggregation induced by canatoxin, a convulsant protein: evidence for the involvement of the platelet lipoxygenase pathway.
Canatoxin is a toxic protein isolated from Canavalia ensiformis seeds. It induces death preceded by convulsions of spinal cord origin and also produces in vitro aggregation of platelets in rabbit, human and guinea-pig plasma. The aggregating effect is dose-dependent at nanomolar concentrations. Rabbit platelets pretreated with canatoxin became refractory to a second exposure to this protein or to collagen, but were still responsive to ADP, Paf-acether or arachidonic acid. [14C]-5-hydroxytryptamine was released from pre-labelled platelets on stimulation with canatoxin. Washed rabbit platelets, but not thrombin-degranulated ones, aggregated on stimulation with canatoxin provided that fibrinogen was added before the toxin. Canatoxin's pro-aggregating activity was inhibited by mepacrine, EDTA, caffeine, prostacyclin, adenosine monophosphate and also by the ADP scavenger system, creatine phosphokinase/creatine phosphate. Furthermore, 3-amino-1-[m-(trifluoromethyl)-phenyl]-2-pyrazoline (BW 755C), eicosatetraynoic acid (ETYA) and nordihydroguaiaretic acid (NDGA) were potent inhibitors of canatoxin-induced aggregation. In contrast, no inhibition was seen with indomethacin. The data indicate that canatoxin is mainly a release-reaction-promoting agent, being devoid of any direct aggregating activity. Thus the aggregation is totally dependent on the release of ADP. Furthermore, canatoxin-induced platelet activation is probably dependent on platelet phospholipase A2 and lipoxygenase activity but is not dependent on cyclo-oxygenase products or the release of Paf-acether.
D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D001091:Arachidonate Lipoxygenases; D001792:Blood Platelets / Q000187:drug effects*; D002110:Caffeine / Q000494:pharmacology; D003402:Creatine Kinase / Q000378:metabolism; D004347:Drug Interactions; D004492:Edetic Acid / Q000494:pharmacology; D011464:Epoprostenol / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007213:Indomethacin / Q000494:pharmacology; D037102:Lectins / Q000494:pharmacology*; D008084:Lipoxygenase / Q000097:blood*; D010725:Phosphocreatine / Q000378:metabolism; D010940:Plant Proteins; D010974:Platelet Aggregation / Q000187:drug effects*; D011796:Quinacrine / Q000494:pharmacology; D011817:Rabbits; D013045:Species Specificity; D013574:Synaptosomes / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology; D014118:Toxins, Biological / Q000494:pharmacology*
D007202:Indicators and Reagents; D037102:Lectins; D010940:Plant Proteins; D014118:Toxins, Biological; D010725:Phosphocreatine; D015117:5,8,11,14-Eicosatetraynoic Acid; D002110:Caffeine; D000249:Adenosine Monophosphate; C032815:canatoxin; D004492:Edetic Acid; D011464:Epoprostenol; D001091:Arachidonate Lipoxygenases; D008084:Lipoxygenase; D003402:Creatine Kinase; D013917:Thrombin; D011796:Quinacrine; D007213:Indomethacin