Fig. 7. Freeze-fracture views of lipid droplet-ER membrane associations in lipid-laden macrophages. (A) Lipid droplet (LD) situated in a cup formed from ER membranes. The lipid droplet has been convexly fractured to reveal the E-face equivalent (eq) of its outermost monolayer. Portions of the P-face and the E-face of the ER membranes are revealed; in this instance, the membrane adjacent to the lipid droplet is seen in P-face view, and portions of the partner ER membrane in E-face view. Note that both ER membranes constitute the cup that partially envelops the lipid droplet. The lipid droplet extends beneath both the ER membranes at the bottom of the field. As the ER membranes extend from the area of association with the lipid droplet, the lumen of the ER becomes larger. (B) `Bird's-eye' view into an ER cup at a site of lipid droplet association. The fracture plane has followed the plane of the ER membranes within a cup, making a concave fracture, and scooping away the lipid droplet so that only the ER membranes remain. Portions of the E-face of the ER membrane closest to the lipid droplet, and of the P-face of the partner membrane distant, are revealed. This image again confirms that at the site of lipid-droplet association, both ER membranes participate in the cup, with the lipid droplet itself lying close to but external to them. As in A, the two membranes of the ER are much closer together at the site of apposition to the lipid droplet. Bars, 0.2 µm.