Figure 10. Freeze-fracture immunogold labeling (FRIL) of the Cx50 COOH-terminus in different gap junction configurations. FRIL showing the specific labeling of the COOH-terminus of chick Cx50 antibody in gap junctions in the outer cortex (A, B) and in the inner cortex (C-F) at high magnification. In the young outer cortical fibers (OC), immunogold labeling of the Cx50 COOH-terminus antibody can be observed specifically on the P-face (A) and E-face (B) of gap junctions with loosely-packed connexons. However, a considerably smaller number of immunogold labeling (particle) of the Cx50 COOH-terminus antibody is seen in gap junctions with a mixture of crystalline-packed (arrows) and loosely-arranged (open arrows) connexons in the inner cortex (C-F). Note that only a single immunogold particle (arrow) is seen in this GJ with crystalline-packed connexons in (F). For comparison, in the embryonic chick lens (G) in which the gap junctions do not display the distinct crystalline-packed connexons [7], many immunogold particles can be observed in the gap junction with cholesterol-free and non-crystalline-packed connexons. The scale bars indicate 100 nm.