[3H]52770 RP, a platelet-activating factor receptor antagonist, and tritiated platelet-activating factor label a common specific binding site in human polymorphonuclear leukocytes.
In human polymorphonuclear leukocytes (PMNs), the tritiated platelet activating factor ([3H]PAF) labels in a saturable manner a single class of binding sites with a Kd of 3.5 +/- 0.5 nM (n = 7) and a maximum binding capacity (Bmax) of 206 +/- 13 fmol/2.5 X 10(6) PMNs (n = 7). 52770 RP, a nonphospholipid antagonist of PAF receptors, fully and competitively displaced the [3H]PAF from its binding sites with a Ki of 7.0 +/- 0.7 nM (n = 4). The high potency and the low solubility in cellular membranes of this compound led us to prepare [3H]52770 RP. This ligand was characterized by a binding which was rapid, reversible, confined to a single site, saturable, specific and stereoselective. Its Kd and Bmax were 4.2 +/- 0.3 nM and 181 +/- 11 fmol/2.5 X 10(6) PMNs, respectively. The stereoselectivity of the binding was suggested by the 600- and 1050-fold higher potency of the d-enantiomer with respect to l-52770 RP in displacing [3H]52770 RP or [3H]PAF, respectively. Several PAF analogs (e.g., lyso-PAF, 2-O-methyl-lyso-PAF), which are poorly active as PAF receptor agonists in functional tests, were weak displacers of [3H]PAF and [3H]52770 RP. Furthermore, for a series of 14 known PAF receptor agonists or antagonists belonging to different chemical families, there was an excellent correlation (r = 0.98) between their ability to displace [3H]PAF and [3H]52770 RP. Thus, [3H]52770 RP and [3H]PAF appear to interact with the same binding site on human PMNs which is proposed to be the PAF receptor mediating functional responses.(ABSTRACT TRUNCATED AT 250 WORDS)
Marquis
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O
Rhône-Poulenc Santé, Centre de Recherche de Vitry, Biology Department, Vitry-sur-Seine, France.
Robaut
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C
Cavero
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I
D001665:Binding Sites; D001667:Binding, Competitive; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D009504:Neutrophils / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010980:Platelet Membrane Glycoproteins; D011725:Pyridines / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000187:drug effects*; D043562:Receptors, G-Protein-Coupled; D013237:Stereoisomerism; D013844:Thiazoles / Q000378:metabolism*; D014316:Tritium
D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D011725:Pyridines; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D013844:Thiazoles; C039351:platelet activating factor receptor; D014316:Tritium; C053706:N-(3-chlorophenyl)-3-(3-pyridinyl)-1H,3H-pyrrolo(1,2-c)thiazole-7-carboxamide