(/sup 3/H)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 ((/sup 3/H)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 (/sup 3/H)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 (/sup 3/H)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 (/sup 3/H)52770 RP or (/sup 3/H)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 (/sup 3/H)PAF and (/sup 3/H)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 (/sup 3/H)PAF and (/sup 3/H)52770 RP. Thus, (/sup 3/H)52770 RP and (/sup 3/H)PAF appear to interact with the same binding site on human PMNs which is proposed to be the PAF receptor mediating functional responses.
- Research Organization:
- Centre de Recherche de Vitry, Vitry-sur-Seine (France)
- OSTI ID:
- 5175935
- Journal Information:
- J. Pharmacol. Exp. Ther.; (United States), Vol. 244:2
- Country of Publication:
- United States
- Language:
- English
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