Separate receptors for prostacyclin and prostaglandin E2 on human gel-filtered platelets.
Human gel-filtered platelets (GFP) and radiolabeled prostacyclin (PGI2), prostaglandin (PG) E2 and PGE1 were used to ascertain whether PGI2 and PGs of the E series share a common receptor or have their own specific receptors on platelets. Attention was given to ensuring the proper experimental conditions to compensate for the rapid half-life of PGI2 at physiologic pH. Specific [3H] PGI2 binding to GFP was maximal at 5 min and pH 7.45. Scatchard analysis indicated a single class of binding sites with an apparent KD of 4.52 X 10(-8) M and 1130 sites per platelet. Approximately 90% of specifically bound [3H]PGI2 could be dissociated by excess unlabeled PGI2 by 5 min. The IC50 for PGI2 was 66 nM. By 5 min, PGE1 and PGE2 were only 7.17 and 0.03%, respectively, as potent inhibitors of binding. Maximal specific binding of either [3H]PGE2 or [3H]PGE1 to GFP occurred by 60 min. During 60-min incubations with [3H]PGE2, the IC50 values for PGE2 and PGE1 were 3 and 6 nM, respectively. When [3H]PGE1 was used, the IC50 values for PGE1 and PGE2 were 30 and 10 nM, respectively. To examine PGI2 competition for [3H] PGE2 and [3H]PGE1 binding sites, 5-min incubation periods were used. PGI2 was only 0.38% as potent an inhibitor of [3H]PGE2 compared to PGE2 and only 30% as potent an inhibitor of [3H] PGE1 compared to PGE1. Scatchard analysis of the 60-min competition experiments using [3H]PGE2 and [3H]PGE1 and the homologous unlabeled ligand yielded curvilinear plots in both instances.(ABSTRACT TRUNCATED AT 250 WORDS)
Eggerman
T L
TL
Andersen
N H
NH
Robertson
R P
RP
D000527:Alprostadil / Q000378:metabolism; D001792:Blood Platelets / Q000032:analysis*; D002850:Chromatography, Gel; D015232:Dinoprostone; D011464:Epoprostenol / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D011458:Prostaglandins E / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000032:analysis*; D044006:Receptors, Epoprostenol; D011982:Receptors, Prostaglandin / Q000032:analysis*; D018078:Receptors, Prostaglandin E; D014316:Tritium
D011458:Prostaglandins E; D011956:Receptors, Cell Surface; D044006:Receptors, Epoprostenol; D011982:Receptors, Prostaglandin; D018078:Receptors, Prostaglandin E; D014316:Tritium; D011464:Epoprostenol; D000527:Alprostadil; D015232:Dinoprostone