Specific binding of [3H]dihydrokadsurenone to rabbit platelet membranes and its inhibition by the receptor agonists and antagonists of platelet-activating factor.
Kadsurenone inhibits specifically and competitively the specific binding of 3H-labeled platelet-activating factor ([3H]PAF) to rabbit platelet membranes. Since the 5-propyl analog of kadsurenone (dihydrokadsurenone) retains roughly the same potency as kadsurenone, [3H]dihydrokadsurenone was therefore synthesized through tritiation of kadsurenone. Specific binding of [3H]dihydrokadsurenone in rabbit platelet membranes is saturable. Scatchard analysis of binding data reveals the presence of a single class of binding sites with an equilibrium dissociation constant (KD) of 16.81 ( +/- 0.57) nM. The total number (Bmax) of detectable binding sites is 2.27 ( +/- 0.09) pmol/mg protein. Both C16- and C18-PAF fully displace the specific binding of (3H]dihydrokadsurenone (5 nM) with an identical ED50 of 3.6 X 10(-9) M. Dihydrokadsurenone and kadsurenone also displace the specific binding with roughly the same potency (ED50 = 4.4 X 10(-8) M). Several other PAF analogs and PAF receptor antagonists tested show relative potencies roughly similar to those found in the [3H]PAF-specific binding assay. Other pharmacological agents with no PAF antagonistic activities did not inhibit the specific binding of [3H]dihydrokadsurenone. These results agree with our previous conclusion that kadsurenone is a specific and competitive receptor antagonist and strongly suggest that PAF and the PAF receptor antagonists tested may interact at a common binding site in the PAF receptor.
D000818:Animals; D001572:Benzofurans / Q000097:blood* / Q000138:chemical synthesis / Q000494:pharmacology; D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D007700:Kinetics; D010972:Platelet Activating Factor / Q000378:metabolism* / Q000494:pharmacology; D010980:Platelet Membrane Glycoproteins; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D014316:Tritium
D001572:Benzofurans; D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; C039351:platelet activating factor receptor; D014316:Tritium; C050160:dihydrokadsurenone