Figure 10. Gap junctions can be displayed as transmission electron microscope (TEM) image density profiles for homocellular (black lines) and heterocellular (dotted lines) pairings. A central 12–13 nm wide pentalaminar zone with three sharp dense bands representing membrane protein density is common to all retinal gap junctions. But the flanking cytoplasmic compartments differ markedly. Homocellular gap junctions between pairs of AII amacrine cells show little protein density near the membrane. Conversely, heterocellular gap junctions between AII amacrine cells and cone bipolar cells show thick bands of protein density extending about 10 nm and over 15 nm from the bipolar cell and amacrine cell faces, respectively.