Measurement of thromboxane A2-induced elevation of ionized calcium in collagen-stimulated platelets with the photoprotein, aequorin.
Using aequorin-loaded rat platelets stimulated with collagen, we found two phases of Ca2+ mobilization, one coinciding with a shape change and the other with aggregation, which have not yet been detected in quin2-loaded platelets. U46619, a stable analogue of prostaglandin H2, induced only a shape change and a concomitant rapid rise in the cytoplasmic ionized calcium concentration ([Cai2+]). However, upon addition of U46619 to platelets previously stimulated with collagen in the presence of indomethacin, a rapid increase in [Cai2+] and a shape change occurred, and, after about 1 min, second increase in [Cai2+] and aggregation occurred. The actions of U46619 were inhibited by an antagonist for the thromboxane A2 (TXA2) receptor. These results suggest that the collagen-induced shape change is initiated by TXA2-induced Ca2+ mobilization, and aggregation is induced by the secondary Ca2+ mobilization induced by TXA2 and the occupation of the receptor by collagen.
T
T
Nakano
A
A
Terawaki
H
H
Arita
D000331:Aequorin; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000097:blood*; D003094:Collagen / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D008164:Luminescent Proteins; D010974:Platelet Aggregation / Q000187:drug effects; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D051381:Rats; D013928:Thromboxane A2 / Q000378:metabolism / Q000494:pharmacology*
D008164:Luminescent Proteins; D011450:Prostaglandin Endoperoxides, Synthetic; D000331:Aequorin; D013928:Thromboxane A2; D003094:Collagen; D002118:Calcium; D007213:Indomethacin