Comparison of the effects of phorbol 12-myristate 13-acetate and prostaglandin E1 on calcium regulation in human platelets.
We compared the effects of phorbol 12-myristate 13-acetate (PMA) with those of prostaglandin E1 (PGE1) on the calcium transient in intact platelets and on 45Ca2+ uptake in saponin-treated platelets and microsomal fractions to determine the roles of protein kinase C and cyclic AMP in calcium sequestration. In intact platelets, PMA, like PGE1, stimulated the return of the calcium transient to resting values after a thrombin stimulus, but only the PGE1 effect was reversed by adrenaline. Both PMA and PGE1, when added before saponin, stimulated ATP-dependent 45Ca2+ uptake into the permeabilized platelets. Thrombin also stimulated 45Ca2+ uptake into saponin-treated platelets. Uptake of 45Ca2+ was increased in microsomal preparations from platelets pretreated with PMA or PGE1. PMA did not increase the cyclic AMP content of control or thrombin-treated platelets, and it induced a pattern of protein phosphorylation in 32P-labelled platelets different from that with PGE1. In correlation with the increased uptake of calcium in the saponin-treated preparation, we measured a rapid translocation of protein kinase C from supernatant to cell fraction after the addition of PMA. Our results suggest that activation of protein kinase C enhances calcium sequestration independently of an effect on cyclic AMP content in platelets. This activation could play a physiological role in the regulation of the calcium transient.
Yoshida
K
K
Department of Anatomy, School of Medicine, University of Pennsylvania, Philadelphia 19104-6058.
Stark
F
F
Nachmias
V T
VT
D000527:Alprostadil / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism; D002118:Calcium / Q000097:blood*; D000242:Cyclic AMP / Q000097:blood; D006801:Humans; D066298:In Vitro Techniques; D008861:Microsomes / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000097:blood; D012503:Saponins / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013917:Thrombin / Q000494:pharmacology
D001798:Blood Proteins; D012503:Saponins; D000242:Cyclic AMP; D011493:Protein Kinase C; D013917:Thrombin; D000527:Alprostadil; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium