A section through the bilayer showing strong densities in the inner-leaflet hydrophobic core attributable to tight packing of the phospholipid hydrocarbon chains. The densities (HC) extend into the hydrophobic core about the same distance as would the sterol group of cholesterol. A matching slice through the model (PDB entry 6uwz) and two (manually inserted) sterol groups are superimposed on and next to one of the receptors to indicate the locations of two of the cholesterol sites identified in Fig. 3; arrows point to the equivalent sites on the other (twofold-related) receptor. Bars on the right indicate the levels of the sections in Figs. 3(a) and 3(b). The figure is shown in inverted contrast. The subunit colours are the same as those used in Fig. 3.