title: Effects of prostaglandins, cAMP, and changes in cytosolic calcium on platelet aggregation induced by a thromboxane A2 mimic (U46619).
abstract: The effects of U46619, a thromboxane mimic, on cytosolic Ca2+ concentration and platelet aggregation were determined in human platelets. Cytosolic Ca2+ concentration was determined by Quin-2 fluorescence and platelet aggregation quantitated with an aggregometer. Addition of U46619 (1 x 10(-7) M) to the platelet suspension produced a rapid increase in cytosolic Ca2+ and platelet aggregation. Pretreatment of platelets with EGTA (3 x 10(-3) M), verapamil (5 x 10(-4) M), a calcium entry blocker, or 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (1 x 10(-3) M), an inhibitor of intracellular Ca2+ release, either blunted or markedly delayed the rate, but not the magnitude, of increase in cytosolic Ca2+ and prevented platelet aggregation by U46619. Pretreatment of platelets with prostaglandin I2 (PGI2) (5 x 10(-8) M), PGD2 (5 x 10(-8) M), PGE1 (5 x 10(-8) M), PGF2 alpha (1 x 10(-5) M), dibutyryl cAMP (5 x 10(-3) M), or forskolin (1 x 10(-6) M) prevented both the increase in cytosolic Ca2+ and the associated platelet aggregation induced by U46619. These data suggest that U46619 may induce platelet aggregation through an increase in cytosolic Ca2+, and that both Ca2+ entry and its release from intracellular storage sites probably contribute to the increase in cytosolic Ca2+. Furthermore, the rate of the increase in cytosolic Ca2+ concentration, as well as the magnitude of the increase, appear to be critical for platelet aggregation induced by U46619. Our data are consistent with the hypothesis that PGs inhibit U46619-induced platelet aggregation by preventing the increase in cytosolic Ca2+, and that these effects may be mediated via an increase in cAMP, since they were induced by PGs and cAMP.
authors.affiliation: Department of Physiology and Biophysics, Howard University College of Medicine, Washington, DC 20059.
authors.forename: J C
authors.initials: JC
authors.lastname: Yun
authors.forename: K P
authors.initials: KP
authors.lastname: Ohman
authors.forename: J R
authors.initials: JR
authors.lastname: Gill
authors.forename: H
authors.initials: H
authors.lastname: Keiser
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000328:Adult; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008297:Male; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology*; D011453:Prostaglandins / Q000494:pharmacology*; D013928:Thromboxane A2 / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D010975:Platelet Aggregation Inhibitors; D011450:Prostaglandin Endoperoxides, Synthetic; D011453:Prostaglandins; D005576:Colforsin; D004533:Egtazic Acid; D013928:Thromboxane A2; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D003994:Bucladesine; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D014700:Verapamil; D000242:Cyclic AMP; D002118:Calcium