Cobra venom cardiotoxin induces aggregation of washed rat platelets: dual effects of Ca2+.
The effects of cardiotoxin isolated and purified from the venom of Naja naja atra on the platelet aggregation were investigated using washed rat platelets prepared chromatographically. In the presence of 1 mM Ca2+, cardiotoxin concentration-dependently induced aggregation of platelets. While extracellular Ca2+ was necessary for the induction of aggregation by cardiotoxin, high concentration of Ca2+ (e.g., 5 mM) prevented cardiotoxin-induced aggregation. Cardiotoxin-induced platelet aggregation was also blocked by 1 mM Ni2+ but not by 100 microM indomethacin or 1 microM nifedipine, indicating that cardiotoxin-induced platelet aggregation involved Ca(2+)-entry pathway other than L-type Ca2+ channels. High concentration of Ca2+ may prevent cardiotoxin-induced aggregation by competing with cardiotoxin for binding site on the platelet membranes.
Huang
S J
SJ
Department of Physiology, Faculty of Medicine, University of Hong Kong, Pokfulam, Hong Kong.
Kwan
C Y
CY
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects*; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D002845:Chromatography; D004179:Cobra Cardiotoxin Proteins / Q000494:pharmacology*; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004347:Drug Interactions; D007213:Indomethacin / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D051381:Rats
D002121:Calcium Channel Blockers; D004179:Cobra Cardiotoxin Proteins; D016861:Cyclooxygenase Inhibitors; D002118:Calcium; D007213:Indomethacin