Distinct platelet-activating factor binding sites in synaptic endings and in intracellular membranes of rat cerebral cortex.
The binding of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (AGEPC or PAF, platelet-activating factor) to synaptic plasma membranes, microsomal membranes, and other rat cerebral cortex subcellular fractions was studied. Using several PAF-binding antagonists, three distinct sites were identified. Two of them were in intracellular membranes (microsomes) and one in synaptic plasma membranes. Microsomal membranes were prepared after obtaining a 43,500 x g pellet from the postmitochondrial supernatant and subsequent centrifugation at 105,000 x g of the resulting supernatant. Most plasma membrane markers were retained in the 43,500 x g pellet (Sun, G.Y., Huang, H.-M., Kelleher, J.A., Stubbs, E.B., Sun, A. Y. (1988) Neurochem. Int. 12, 69-77). Microsomes were purified by density-gradient centrifugation and marker enzymes showed relatively very low contamination by plasma membrane markers. Myelin and mitochondria were devoid of specific PAF binding. A site displaying the highest PAF-binding affinity reported to date in all cells and membranes (KD = 22.5 +/- 1.7 pM and Bmax 8.75 = fmol/mg protein), was found in the microsomal fraction. There was a second binding site in microsomal fractions (KD = 25.0 +/- 0.8 nM and Bmax = 0.96 pmol/mg protein. Ca2+ decreases PAF affinity for the microsomal binding sites. The third binding site displays relatively low specific PAF binding and is present in synaptosomal plasma membranes. Moreover, displacement curves by a wide variety of PAF antagonists indicated different affinities for each of the binding sites described here. These results indicate that PAF-binding sites are heterogeneous in rat cerebral cortex, and they imply that the microsomal membrane sites may be involved, at least in part, in intracellular events such as gene expression.
Marcheselli
V L
VL
Louisiana State University Medical Center School of Medicine, New Orleans 70112.
Rossowska
M J
MJ
Domingo
M T
MT
Braquet
P
P
Bazan
N G
NG
D000818:Animals; D001667:Binding, Competitive; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D002540:Cerebral Cortex / Q000648:ultrastructure*; D004224:Diterpenes; D046934:Ginkgolides; D007425:Intracellular Membranes / Q000378:metabolism*; D007783:Lactones / Q000494:pharmacology; D008297:Male; D008861:Microsomes / Q000648:ultrastructure; D008928:Mitochondria / Q000648:ultrastructure; D010742:Phospholipid Ethers / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000378:metabolism; D010980:Platelet Membrane Glycoproteins; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D013569:Synapses / Q000378:metabolism*; D013570:Synaptic Membranes / Q000378:metabolism
D004224:Diterpenes; D046934:Ginkgolides; D007783:Lactones; D010742:Phospholipid Ethers; D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; C039351:platelet activating factor receptor; C037913:CV 3988; C045856:ginkgolide B