VISUALIZATION OF THE TRANSPORT PATHWAYS OF LOW-DENSITY LIPOPROTEINS ACROSS THE ENDOTHELIAL-CELLS IN THE BRANCHED REGIONS OF RAT ARTERIES

The transport pathways of low density lipoproteins (LDL) across the en dothelium at the branched and unbranched regions of the artery were st udied in high cholesterol diet-fed rats. Rat tissues were analyzed by perfusing in situ human or rat LDL labeled with colloidal gold or fluo rescein -dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). Results indicated that more LDL-DiI accumulated in the branche d regions than in the unbranched regions of the artery. LDL-gold conju gates were observed in the plasmalemmal vesicles, multivesicular bodie s and in the subendothelial space in both the branched and the unbranc hed regions of the arteries. Quantitative study revealed that the volu me densities of plasmalemmal vesicles which contained the LDL-gold par ticles in the branched regions of the aortic arch were significantly ( P < 0.05) higher than the density value in the unbranched regions of t he thoracic aorta, whereas there was no marked difference in the densi ty value of multivesicular bodies between these two regions. The open junctions with gap widths of 30-450 nn between adjacent endothelial ce lls were only observed in the branched regions of the aortic arch, whe reas no open junctions were present in the unbranched regions of the t horacic aorta. Moreover, the LDL-gold conjugates were present within m ost of these open junctions. In all specimens examined, no gold partic les were found in the normal intercellular channels (i.e., 25 nm and l ess) of both regions. These results indicated that the major visible r outes for transport of LDL across the endothelium in the branched regi ons of the arteries are open junctions as well as plasmalemmal vesicle s. The region-associated permeability changes of LDL might account for the incidence of atherosclerosis in the branched areas of arteries.