Characterization of specific binding sites of 3H-labelled platelet-activating factor ([3H]PAF) and a new antagonist, [3H]SR 27417, on guinea-pig tracheal epithelial cells.
Binding of 3H-labelled platelet-activating factor ([3H]PAF) to guinea-pig tracheal epithelial cells was time-dependent, reversible and saturable. Scatchard analysis of the saturation-binding data indicated that [3H]PAF bound to one class of specific binding sites with high affinity (KD = 4.3 +/- 0.03 nM; Bmax. = 0.172 +/- 0.02 fmol/10(5) cells; n = 3). Unlabelled PAF competitively and selectively inhibited the specific binding of [3H]PAF with 50% inhibition at 4.8 +/- 0.07 nM (n = 3). SR 27417, the first member of a newly developed PAF antagonist series, competitively displaced [3H]PAF from its binding sites on guinea-pig tracheal epithelial cells with a Ki of 100 +/- 3 pM (n = 3). Studies carried out in parallel demonstrated that SR 27417 was 40 times more potent than C16-PAF itself and more than 100-fold as active as the best synthetic PAF-receptor antagonist yet described. [3H]SR 27417 displayed high-affinity, specific, reversible as well as saturable binding to a single class of binding sites on tracheal epithelial cells (KD = 94 +/- 7 pM; Bmax. = 0.181 +/- 0.04 fmol/10(5) cells; n = 3). C16-PAF, lyso-PAF, enantio-PAF, SR 27417 and other PAF-receptor antagonists had Ki values which were nearly identical for both [3H]PAF and [3H]SR 27417, demonstrating that in guinea-pig tracheal epithelial cells they have the same binding sites. In conclusion, these data suggest that tracheal epithelial cells contain PAF-specific receptors and indicate that SR 27417 is an extremely potent PAF-receptor antagonist, as well as being a suitable radioligand for labelling PAF receptors on intact cells.
Herbert
J M
JM
Haemobiology Research Department, Sanofi Recherche, Toulouse, France.
D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors* / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled; D013844:Thiazoles / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D014132:Trachea / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D014316:Tritium
D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D013844:Thiazoles; C039351:platelet activating factor receptor; D014316:Tritium; C071317:Foropafant