title: Uptake of radiolabeled and colloidal gold-labeled chyle chylomicrons and chylomicron remnants by rat platelets in vitro.
abstract: This study examined the uptake of chyle chylomicrons (CMs) and chylomicron remnants (CMRs) by rat platelets in vitro. CMs and CMRs were doubly labeled with [3H]arachidonate ([3H]-20:4) and [14C]cholesterol and were incubated with platelets for up to 4 hours. A significant uptake (binding and/or internalization) of CMs by the platelets occurred, as indicated by the parallel increase of [3H]20:4 and [14C]cholesterol in platelets with incubation time. Addition of unlabeled CMs, VLDLs, LDLs, and HDLs decreased the uptake of labeled CMs. The competition experiments suggested that there is both a saturable binding and a nonspecific uptake of CMs. During incubation with CMs, the proportion of [3H]20:4 in phospholipids decreased and that in 1,2-x-diacylglycerol increased. The data indicated that a phospholipase C-mediated degradation of phosphatidylcholine and phosphatidylethanolamine occurred, whereas [3H]20:4 in triglyceride and 14C in cholesterol ester did not change. Electron microscopic studies after incubation with colloidal gold-labeled CMs (CM-Au's) demonstrated an accumulation of CM-Au particles in the open canalicular system of the platelets. Some CM-Au particles were localized in cytoplasmic vacuoles that were not stained by ruthenium red. Some CM-Au's or free gold particles were in vacuoles that showed acid phosphatase activity, indicating that some true endocytosis of CM occurred. The uptake of [3H]-20:4- and [14C]cholesterol-labeled CMRs was low compared with the uptake of CMs. After incubation with colloidal gold-labeled CMRs (CMR-Au's), only a few platelets contained CMR-Au in their open canalicular systems, and no CMR-Au particles were seen in the cytoplasm or in acid phosphatase-positive vacuoles. Rat platelets can thus interact with CMs by a process that leads to a sequestration in the open canalicular system and endocytosis and a net degradation of CM phospholipids. The conversion of CMs to CMRs counteracts this interaction.
authors.affiliation: Department of Cell Biology 1, University Hospital of Lund, Sweden.
authors.forename: N
authors.initials: N
authors.lastname: Xu
authors.forename: L
authors.initials: L
authors.lastname: Zhou
authors.forename: R
authors.initials: R
authors.lastname: Odselius
authors.forename: A
authors.initials: A
authors.lastname: Nilsson
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002784:Cholesterol / Q000378:metabolism; D002913:Chyle / Q000378:metabolism*; D002914:Chylomicrons / Q000378:metabolism*; D003102:Colloids; D006046:Gold; D006651:Histocytochemistry; D050356:Lipid Metabolism; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D017207:Rats, Sprague-Dawley; D013194:Staining and Labeling; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D002914:Chylomicrons; D003102:Colloids; D014316:Tritium; D006046:Gold; D002784:Cholesterol