title: Homologous desensitization of human platelet thromboxane A2/prostaglandin H2 receptors.
abstract: Desensitization of platelet thromboxane (TX)A2/prostaglandin (PG)H2 receptors was induced by incubating platelet-rich plasma with the stable PGH2 analog 11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619) (1 microM). Iloprost, a stable prostacyclin analog, was included in the incubation to prevent platelet activation. The TXA2 mimetic, [1S-1 alpha,2 beta(5Z), 3 alpha(1E,3S*), 4 alpha)]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo - [2.2.1]heptan-2-yl]-5-heptenoic acid (I-BOP), was used to induce platelet aggregation, shape change and increases in intracellular free calcium. The EC50 values for I-BOP-induced rise in intracellular free calcium (control = 10.2 +/- 1.5 nM; desensitized = 79.4 +/- 22.4 nM, n = 6, P less than .05), aggregation (control = 15.8 +/- 2.4 nM; desensitized = 51.7 +/- 11.9 nM; P less than .05, n = 5) and shape change (control = 172 +/- 37 pM; desensitized = 350 +/- 60 pM; P less than .05, n = 7) were increased by the preincubation with U46619. Aggregation responses to thrombin and the calcium ionophore, ionomycin, were unaltered by the preincubation with U46619. Equilibrium binding studies at pH 7.4 revealed a decrease in the number of binding sites for the receptor antagonist 9,11-dimethylmethano-11,12- methano-16(3-iodo-4-hydroxyphenyl)-13,14-dihydro-13-aza-15 alpha beta-omega- tetranor-TXA2 [125I]PTA-OH) (control = 3246 +/- 509 sites/platelet, desensitized = 2198 +/- 324 sites/platelet, n = 6, P less than .05) without a change in affinity.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Cell and Molecular Pharmacology, Medical University of South Carolina, Charleston.
authors.forename: A K
authors.initials: AK
authors.lastname: Okwu
authors.forename: M E
authors.initials: ME
authors.lastname: Ullian
authors.forename: P V
authors.initials: PV
authors.lastname: Halushka
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D001665:Binding Sites; D001667:Binding, Competitive; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D001643:Bridged Bicyclo Compounds / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D006801:Humans; D016285:Iloprost / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology*; D011982:Receptors, Prostaglandin / Q000187:drug effects* / Q000378:metabolism; D017482:Receptors, Thromboxane; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
chemical_list: D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005231:Fatty Acids, Unsaturated; D011450:Prostaglandin Endoperoxides, Synthetic; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D014662:Vasoconstrictor Agents; C061750:7-(3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo(2.2.1)heptan-2-yl)-5-heptenoic acid; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D016285:Iloprost