Octylonium bromide interacts competitively with the PAF receptor.
To clarify the nature of the interaction of octylonium bromide with the PAF receptor, saturation studies of 3H-PAF binding were made in the presence of increasing concentrations of the radioligand (from 0.06 to 7.4 nM) and of octylonium bromide (1 X 10(-8), 5 X 10(-8) and 1 X 10(-7) M) or of a potent PAF antagonist L 652,731 (2.5 X 10(-7) M), or in the absence of competing drugs. Saturation binding data were plotted according to the non-linear fitting analysis and to Scatchard transformation. Both mathematical models indicated that the presence of added drugs decreased the affinity of the complex 3H-PAF/PAF receptors, leaving unaffected the maximum number of PAF binding sites. Receptor parameters in the absence of competitors were: KD = 1.2 nM, Bmax = 950 fmoles 3H-PAF bound/10(8) platelets. Octylonium bromide increased, in a concentration-dependent manner, KD values from 1.5 to 2.1 nM, while Bmax ranged from 910 to 980 fmoles 3H-PAF specifically bound/10(8) platelets. Likewise, L 652,731 did not influence Bmax (980 fmoles) but increased KD (1.9 nM). The binding behaviour of octylonium bromide and L 652,731 indicates that the two compounds inhibit competitively the binding of 3H-PAF to its receptors.
Barone
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Istituto di Ricerche Biomediche A. Marxer, Ivrea, Italy.
Maggi
C A
CA
Baroldi
P
P
Giachetti
A
A
Meli
A
A
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D010276:Parasympatholytics / Q000378:metabolism / Q000494:pharmacology*; D010980:Platelet Membrane Glycoproteins; D000644:Quaternary Ammonium Compounds / Q000378:metabolism / Q000494:pharmacology*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled
D010276:Parasympatholytics; D010980:Platelet Membrane Glycoproteins; D000644:Quaternary Ammonium Compounds; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; C039351:platelet activating factor receptor; C013934:octylonium