Specific binding of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor) to the intact canine platelet
Binding of 3H-labeled 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor; PAF) to the intact, washed canine platelet has been defined and characterized as being specific and receptor-mediated. Under the conditions described, specific binding to 2 X 10(7) canine platelets reac...
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Veröffentlicht in: | Thrombosis research 1988-06, Vol.50 (6), p.789-802 |
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Sprache: | eng |
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Zusammenfassung: | Binding of 3H-labeled 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor; PAF) to the intact, washed canine platelet has been defined and characterized as being specific and receptor-mediated. Under the conditions described, specific binding to 2 X 10(7) canine platelets reached saturation within 10 min at a [3H]PAF concentration of approximately 0.4 nM. Non-specific binding was accountable for, at most, some 30% of the total PAF bound at equilibrium. Above approximately 0.4 nM [3H]PAF, total binding and non-specific binding increased in parallel. Since no involvement of PAF ligand in dog platelet intermediary metabolism during the binding incubation could be demonstrated, non-specific PAF binding may reflect a partitioning of the molecule into a cellular compartment (perhaps the platelet membranes). Equilibrium analysis revealed that the canine platelet has one class of specific binding sites with a Kd of 0.63 +/- 0.02 nM PAF, a Bmax of 222 +/- 10 fmol/10(7) platelets, and, at most, 1.33 +/- 0.06 X 10(3) binding sites/platelet. [3H]PAF specific binding to the canine platelet is ligand-selective and stereo-selective, as demonstrated by the relative abilities of non-labeled PAF and various PAF analogs/metabolites to inhibit [3H]PAF specific binding in a concentration-dependent manner. The extents to which PAF and PAF analogs were able to displace specifically-bound [3H]PAF from the canine platelet correlated well with their physiological (i. e., pro-aggregatory) effects. These data offer the first quantitative description of canine platelet high-affinity PAF binding sites/receptors and link receptor-mediated PAF binding to canine platelet physiology. |
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ISSN: | 0049-3848 1879-2472 |
DOI: | 10.1016/0049-3848(88)90339-8 |