Biochemical characterization and comparison of rat thromboxane A2/prostaglandin H2 receptors in platelets and cultured aortic smooth muscle cells.
Comparison of thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors in rat cultured vascular smooth muscle cells (VSMC) with those in rat gel-filtered platelets (GFP) was carried out using a receptor-ligand binding assay. The binding of each of three radiolabeled TXA2/PGH2 receptor antagonists [( 3H]S-145,[3H]SQ29,548, and [3H]ONO3708) displayed high affinity and specificity as well as saturable and displaceable binding to a single class of recognition sites with the same maximum number in both VSMC and GFP. The Kd values for [3H]S-145 were almost identical for both VSMC and GFP, whereas the values for [3H]SQ29,548 and [3H]ONO3708 for VSMC were approximately two and six times larger than that for GFP. Kinetic analysis of the binding of each receptor antagonist revealed a smaller K1 value (the association rate constant) for [3H]SQ29,548 and a larger K-1 value (the dissociation rate constant) for [3H]ONO3708 for VSMC compared to GFP, in contrast with almost the same kinetic constants for the [3H]S-145 binding for both cells. Comparison of the inhibitory potencies (Ki values) for [3H]S-145 binding for both VSMC and GFP proved that S-145 had the same affinity for both cells; ONO11120 and BM13177, as well as SQ29,548 and ONO3708, possessed lower affinity for VSMC; and U46619 exhibited higher affinity for VSMC. The rank orders of potency were identical in both cells (S-145 greater than SQ29,548 greater than ONO3708 greater than ONO11120 greater than BM13177), which correlated well with their pharmacological activities. These results suggest a similarity in ligand binding specificity with some differences in the accessibility of the antagonists in the TXA2/PGH2 receptors between platelets and vascular smooth muscles.
Hanasaki
K
K
Shionogi Research Laboratories, Shionogi & Co. Ltd., Osaka, Japan.
Nakano
K
K
Kasai
H
H
Arita
H
H
D000818:Animals; D001667:Binding, Competitive; D001792:Blood Platelets / Q000032:analysis*; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002478:Cells, Cultured; D005229:Fatty Acids, Monounsaturated / Q000378:metabolism; D005231:Fatty Acids, Unsaturated; D006834:Hydrazines / Q000378:metabolism; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D011982:Receptors, Prostaglandin / Q000032:analysis / Q000187:drug effects; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000378:metabolism
D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005229:Fatty Acids, Monounsaturated; D005231:Fatty Acids, Unsaturated; D006834:Hydrazines; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; C056566:S 145; D013928:Thromboxane A2; C045749:SQ 29548; C049855:ONO 3708