CA2+ ENTRY PATHWAYS ACTIVATED BY THE TUMOR PROMOTER THAPSIGARGIN IN HUMAN PLATELETS

Citation
Y. Hashimoto et al., CA2+ ENTRY PATHWAYS ACTIVATED BY THE TUMOR PROMOTER THAPSIGARGIN IN HUMAN PLATELETS, Biochimica et biophysica acta, 1220(1), 1993, pp. 37-41
Citations number
28
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Biophysics,Biology
ISSN journal
0006-3002
Volume
1220
Issue
1
Year of publication
1993
Pages
37 - 41
Database
ISI
SICI code
0006-3002(1993)1220:1<37:CEPABT>2.0.ZU;2-U
Abstract
Thapsigargin-activated Ca2+ entry into platelets was examined in the p resence of S-145, a thromboxane A2 receptor antagonist, to inhibit ind irect effects by endogenously formed prostaglandin H-2/thromboxane A2. With external Ca2+ present, 0.2 muM thapsigargin caused a prompt incr ease in intracellular Ca2+ concentration ([Ca2+]i) followed by a gradu al increase. Pretreatment with 6 muM wortmannin, a specific inhibitor of myosin light chain kinase, partly inhibited the increase in [Ca2+]i . In Ca2+-free EGTA buffer, thapsigargin induced a smaller increase in [Ca2+]i, and subsequent addition of Ca2+ to the buffer caused a furth er prompt increase in [Ca2+]i, demonstrating external Ca2+ entry. Wort mannin only partly inhibited this entry of external Ca2+. The wortmann in-insensitive Ca2+ entry pathway remained open for more than 6 min in Ca2+-free buffer. On the other hand, when receptor agonists such as t hrombin and U46619 were substituted for thapsigargin, activation of th e wortmannin-insensitive Ca2+ entry was transient (Hashimoto et al., J . Biol. Chem (1992) 267, 17078-17081). In the presence of S-145 and wo rtmannin, thapsigargin stimulated phosphorylation of neither the 20-kD a myosin light chain nor the 47-kDa protein, a substrate of protein ki nase C. These results suggest that thapsigargin induces external Ca2entry by two mechnisms: (1) a mechanism involving myosin light chain k inase; (2) a mechanism, not activated by receptor agonists, that is in dependent of the major protein kinases of platelets.